sergey-chugunov-1985 commented on code in PR #12442:
URL: https://github.com/apache/ignite/pull/12442#discussion_r2473274767


##########
modules/core/src/main/java/org/apache/ignite/topology/MdcTopologyValidator.java:
##########
@@ -0,0 +1,129 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.ignite.topology;
+
+import java.util.Collection;
+import java.util.Objects;
+import java.util.Set;
+import java.util.stream.Stream;
+import org.apache.ignite.cluster.ClusterNode;
+import org.apache.ignite.configuration.TopologyValidator;
+import org.apache.ignite.lang.IgniteExperimental;
+
+/**
+ * Multi-Datacenter Topology Validator.
+ *
+ * <p>This class is used to validate the cluster topology in a 
multi-datacenter (MDC) environment 
+ * by enforcing rules based on the visibility of datacenters.
+ * It provides protection against split-brain scenarios during datacenter 
failures or unavailability due to network issues.</p>
+ *
+ * <p>The validator supports two modes of operation:</p>
+ * <ul>
+ *     <li><strong>Majority-based validation:</strong> When an odd number of 
datacenters are defined, the validator enables 
+ *         data modification operations in the cluster segment that contain a 
majority of datacenters. 
+ *         Any segment containing a minority of datacenters is considered as 
invalid with only read operations available.</li>
+ *     <li><strong>Main Datacenter validation:</strong> When an even number of 
datacenters are defined, a main datacenter
+ *         should be specified. The cluster segment remains write-accessible 
as long as the main datacenter is visible from
+ *         all nodes of that segment.</li>
+ * </ul>
+ *
+ * <p><strong>Usage Requirements:</strong></p>
+ * <ul>
+ *     <li>If number of datacenters is even, specify a main datacenter via 
{@link #setMainDatacenter(String)}.
+ *     Set of datacenters could be left null.</li>
+ *     <li>If number of datacenters is odd, set of datacenter IDs must be 
specified via {@link #setDatacenters(Set)}.
+ *     Main datacenter setting is ignored and could be left null.</li>
+ *     
+ * </ul>
+ *
+ * <p><strong>Example:</strong></p>
+ * <pre>
+ * MdcTopologyValidator mdcValidator = new MdcTopologyValidator();
+ * mdcValidator.setDatacenters(Set.of("DC1", "DC2", "DC3"));
+ * 
+ * CacheConfiguration cacheCfg = new CacheConfiguration("example-cache")
+ *     .setTopologyValidator(mdcValidator)
+ *     // other cache properties.
+ * </pre>
+ *
+ * <p><strong>Note:</strong> This class is marked with the {@link 
IgniteExperimental} annotation and may change in future releases.</p>
+ *
+ * @see TopologyValidator
+ * @since Apache Ignite 2.18
+ */
+@IgniteExperimental
+public class MdcTopologyValidator implements TopologyValidator {
+    /** */
+    private static final long serialVersionUID = 0L;
+
+    /** */
+    private Set<String> dcs;
+
+    /** */
+    private String mainDc;
+
+    /** @param datacenters Datacenters.*/
+    public void setDatacenters(Set<String> datacenters) {
+        dcs = datacenters;
+    }
+
+    /** @param mainDatacenter Main datacenter.*/
+    public void setMainDatacenter(String mainDatacenter) {
+        mainDc = mainDatacenter;
+    }
+
+    /** */
+    public void checkConfiguration() {
+        if (dcs == null && mainDc == null)
+            throw new IllegalStateException("Missing datacenters or main 
datacenter.");
+
+        if (dcs != null && dcs.isEmpty())
+            throw new IllegalStateException("Missing datacenters.");
+
+        if (mainDc != null && dcs != null && dcs.size() % 2 == 1)
+            throw new IllegalStateException("Datacenters count must be even 
when main datacenter is set.");

Review Comment:
   ```suggestion
               throw new IllegalStateException("Uneven number of datacenters 
cannot be used along with main datacenter. Please remove main datacenter 
setting or specify even number of datacenters.");
   ```



##########
modules/core/src/test/java/org/apache/ignite/spi/failover/topology/validator/MdcTopologyValidatorTest.java:
##########
@@ -0,0 +1,333 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.ignite.spi.failover.topology.validator;
+
+import java.util.Set;
+import java.util.concurrent.ThreadLocalRandom;
+import javax.cache.CacheException;
+import org.apache.ignite.IgniteCache;
+import org.apache.ignite.IgniteCheckedException;
+import org.apache.ignite.IgniteException;
+import org.apache.ignite.IgniteSystemProperties;
+import org.apache.ignite.cluster.ClusterState;
+import org.apache.ignite.configuration.CacheConfiguration;
+import org.apache.ignite.configuration.DataRegionConfiguration;
+import org.apache.ignite.configuration.DataStorageConfiguration;
+import org.apache.ignite.configuration.IgniteConfiguration;
+import org.apache.ignite.configuration.TopologyValidator;
+import org.apache.ignite.internal.IgniteEx;
+import org.apache.ignite.testframework.GridTestUtils;
+import org.apache.ignite.testframework.junits.common.GridCommonAbstractTest;
+import org.apache.ignite.topology.MdcTopologyValidator;
+import org.junit.Test;
+
+/** */
+public class MdcTopologyValidatorTest extends GridCommonAbstractTest {
+    /** */
+    private static final String DC_ID_0 = "DC0";
+
+    /** */
+    private static final String DC_ID_1 = "DC1";
+
+    /** */
+    private static final String DC_ID_2 = "DC2";
+
+    /** */
+    private static final String KEY = "key";
+
+    /** */
+    private static final String VAL = "val";
+
+    /** {@inheritDoc} */
+    @Override protected void afterTest() throws Exception {
+        super.afterTest();
+
+        stopAllGrids();
+
+        cleanPersistenceDir();
+
+        System.clearProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID);
+    }
+
+    /** {@inheritDoc} */
+    @Override protected IgniteConfiguration getConfiguration(String 
igniteInstanceName) throws Exception {
+        return super.getConfiguration(igniteInstanceName)
+            .setDataStorageConfiguration(
+                new DataStorageConfiguration()
+                    .setDefaultDataRegionConfiguration(
+                        new DataRegionConfiguration()
+                            .setPersistenceEnabled(true)
+                    )
+            )
+            .setConsistentId(igniteInstanceName);
+    }
+
+    /** */
+    @Test
+    public void testEmptyConfig() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Missing datacenters or main datacenter");
+    }
+
+    /** */
+    @Test
+    public void testOddDcsWithMain() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1, DC_ID_2));
+        topValidator.setMainDatacenter(DC_ID_1);
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Datacenters count must be even when main datacenter is set.");
+    }
+
+    /** Checks 1DC case with MdcTopologyValidator usage.*/
+    @Test
+    public void testEmptyDc() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of());
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Missing datacenters");
+    }
+
+    /** */
+    @Test
+    public void testNodeWitoutDCWithMajority() throws Exception {

Review Comment:
   ```suggestion
       public void testNodeWithoutDcSpecifiedWithMajorityBasedValidator() 
throws Exception {
   ```



##########
modules/core/src/main/java/org/apache/ignite/topology/MdcTopologyValidator.java:
##########
@@ -0,0 +1,129 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.ignite.topology;
+
+import java.util.Collection;
+import java.util.Objects;
+import java.util.Set;
+import java.util.stream.Stream;
+import org.apache.ignite.cluster.ClusterNode;
+import org.apache.ignite.configuration.TopologyValidator;
+import org.apache.ignite.lang.IgniteExperimental;
+
+/**
+ * Multi-Datacenter Topology Validator.
+ *
+ * <p>This class is used to validate the cluster topology in a 
multi-datacenter (MDC) environment 
+ * by enforcing rules based on the visibility of datacenters.
+ * It provides protection against split-brain scenarios during datacenter 
failures or unavailability due to network issues.</p>
+ *

Review Comment:
   ```suggestion
    *
    * <p>
    * In order to use MdcTopologyValidator one has to specify datacenter ID 
attribute on each server node.
    * Datacenter ID is an arbitrary string that can be set with {@link 
IgniteSystemProperties#IGNITE_DATA_CENTER_ID} system property on the node 
startup.
    * All server nodes belonging to the same datacenter should specify the same 
datacenter ID, and nodes in different datacenters should have different 
datacenter IDs.
    * </p>
   ```



##########
modules/core/src/main/java/org/apache/ignite/topology/MdcTopologyValidator.java:
##########
@@ -0,0 +1,129 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.ignite.topology;
+
+import java.util.Collection;
+import java.util.Objects;
+import java.util.Set;
+import java.util.stream.Stream;

Review Comment:
   ```suggestion
   import java.util.stream.Stream;
   import org.apache.ignite.IgniteSystemProperties;
   ```



##########
modules/core/src/main/java/org/apache/ignite/topology/MdcTopologyValidator.java:
##########
@@ -0,0 +1,129 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.ignite.topology;
+
+import java.util.Collection;
+import java.util.Objects;
+import java.util.Set;
+import java.util.stream.Stream;
+import org.apache.ignite.cluster.ClusterNode;
+import org.apache.ignite.configuration.TopologyValidator;
+import org.apache.ignite.lang.IgniteExperimental;
+
+/**
+ * Multi-Datacenter Topology Validator.
+ *
+ * <p>This class is used to validate the cluster topology in a 
multi-datacenter (MDC) environment 
+ * by enforcing rules based on the visibility of datacenters.
+ * It provides protection against split-brain scenarios during datacenter 
failures or unavailability due to network issues.</p>
+ *
+ * <p>The validator supports two modes of operation:</p>
+ * <ul>
+ *     <li><strong>Majority-based validation:</strong> When an odd number of 
datacenters are defined, the validator enables 
+ *         data modification operations in the cluster segment that contain a 
majority of datacenters. 
+ *         Any segment containing a minority of datacenters is considered as 
invalid with only read operations available.</li>
+ *     <li><strong>Main Datacenter validation:</strong> When an even number of 
datacenters are defined, a main datacenter
+ *         should be specified. The cluster segment remains write-accessible 
as long as the main datacenter is visible from
+ *         all nodes of that segment.</li>
+ * </ul>
+ *
+ * <p><strong>Usage Requirements:</strong></p>
+ * <ul>
+ *     <li>If number of datacenters is even, specify a main datacenter via 
{@link #setMainDatacenter(String)}.
+ *     Set of datacenters could be left null.</li>
+ *     <li>If number of datacenters is odd, set of datacenter IDs must be 
specified via {@link #setDatacenters(Set)}.
+ *     Main datacenter setting is ignored and could be left null.</li>
+ *     
+ * </ul>
+ *
+ * <p><strong>Example:</strong></p>
+ * <pre>
+ * MdcTopologyValidator mdcValidator = new MdcTopologyValidator();
+ * mdcValidator.setDatacenters(Set.of("DC1", "DC2", "DC3"));
+ * 
+ * CacheConfiguration cacheCfg = new CacheConfiguration("example-cache")
+ *     .setTopologyValidator(mdcValidator)
+ *     // other cache properties.
+ * </pre>
+ *
+ * <p><strong>Note:</strong> This class is marked with the {@link 
IgniteExperimental} annotation and may change in future releases.</p>
+ *
+ * @see TopologyValidator
+ * @since Apache Ignite 2.18
+ */
+@IgniteExperimental
+public class MdcTopologyValidator implements TopologyValidator {
+    /** */
+    private static final long serialVersionUID = 0L;
+
+    /** */
+    private Set<String> dcs;
+
+    /** */
+    private String mainDc;
+
+    /** @param datacenters Datacenters.*/
+    public void setDatacenters(Set<String> datacenters) {
+        dcs = datacenters;
+    }
+
+    /** @param mainDatacenter Main datacenter.*/
+    public void setMainDatacenter(String mainDatacenter) {
+        mainDc = mainDatacenter;
+    }
+
+    /** */
+    public void checkConfiguration() {
+        if (dcs == null && mainDc == null)
+            throw new IllegalStateException("Missing datacenters or main 
datacenter.");

Review Comment:
   ```suggestion
               throw new IllegalStateException("Either set of datacenters or 
main datacenter should be specified.");
   ```



##########
modules/core/src/main/java/org/apache/ignite/topology/MdcTopologyValidator.java:
##########
@@ -0,0 +1,129 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.ignite.topology;
+
+import java.util.Collection;
+import java.util.Objects;
+import java.util.Set;
+import java.util.stream.Stream;
+import org.apache.ignite.cluster.ClusterNode;
+import org.apache.ignite.configuration.TopologyValidator;
+import org.apache.ignite.lang.IgniteExperimental;
+
+/**
+ * Multi-Datacenter Topology Validator.
+ *
+ * <p>This class is used to validate the cluster topology in a 
multi-datacenter (MDC) environment 
+ * by enforcing rules based on the visibility of datacenters.
+ * It provides protection against split-brain scenarios during datacenter 
failures or unavailability due to network issues.</p>
+ *
+ * <p>The validator supports two modes of operation:</p>
+ * <ul>
+ *     <li><strong>Majority-based validation:</strong> When an odd number of 
datacenters are defined, the validator enables 
+ *         data modification operations in the cluster segment that contain a 
majority of datacenters. 
+ *         Any segment containing a minority of datacenters is considered as 
invalid with only read operations available.</li>
+ *     <li><strong>Main Datacenter validation:</strong> When an even number of 
datacenters are defined, a main datacenter
+ *         should be specified. The cluster segment remains write-accessible 
as long as the main datacenter is visible from
+ *         all nodes of that segment.</li>
+ * </ul>
+ *
+ * <p><strong>Usage Requirements:</strong></p>
+ * <ul>
+ *     <li>If number of datacenters is even, specify a main datacenter via 
{@link #setMainDatacenter(String)}.
+ *     Set of datacenters could be left null.</li>
+ *     <li>If number of datacenters is odd, set of datacenter IDs must be 
specified via {@link #setDatacenters(Set)}.
+ *     Main datacenter setting is ignored and could be left null.</li>
+ *     
+ * </ul>
+ *
+ * <p><strong>Example:</strong></p>
+ * <pre>
+ * MdcTopologyValidator mdcValidator = new MdcTopologyValidator();
+ * mdcValidator.setDatacenters(Set.of("DC1", "DC2", "DC3"));
+ * 
+ * CacheConfiguration cacheCfg = new CacheConfiguration("example-cache")
+ *     .setTopologyValidator(mdcValidator)
+ *     // other cache properties.
+ * </pre>
+ *
+ * <p><strong>Note:</strong> This class is marked with the {@link 
IgniteExperimental} annotation and may change in future releases.</p>
+ *
+ * @see TopologyValidator
+ * @since Apache Ignite 2.18
+ */
+@IgniteExperimental
+public class MdcTopologyValidator implements TopologyValidator {
+    /** */
+    private static final long serialVersionUID = 0L;
+
+    /** */
+    private Set<String> dcs;
+
+    /** */
+    private String mainDc;
+
+    /** @param datacenters Datacenters.*/
+    public void setDatacenters(Set<String> datacenters) {
+        dcs = datacenters;
+    }
+
+    /** @param mainDatacenter Main datacenter.*/
+    public void setMainDatacenter(String mainDatacenter) {
+        mainDc = mainDatacenter;
+    }
+
+    /** */
+    public void checkConfiguration() {
+        if (dcs == null && mainDc == null)
+            throw new IllegalStateException("Missing datacenters or main 
datacenter.");
+
+        if (dcs != null && dcs.isEmpty())
+            throw new IllegalStateException("Missing datacenters.");

Review Comment:
   ```suggestion
               throw new IllegalStateException("Please provide a non-empty set 
of datacenters.");
   ```



##########
modules/core/src/test/java/org/apache/ignite/spi/failover/topology/validator/MdcTopologyValidatorTest.java:
##########
@@ -0,0 +1,333 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.ignite.spi.failover.topology.validator;
+
+import java.util.Set;
+import java.util.concurrent.ThreadLocalRandom;
+import javax.cache.CacheException;
+import org.apache.ignite.IgniteCache;
+import org.apache.ignite.IgniteCheckedException;
+import org.apache.ignite.IgniteException;
+import org.apache.ignite.IgniteSystemProperties;
+import org.apache.ignite.cluster.ClusterState;
+import org.apache.ignite.configuration.CacheConfiguration;
+import org.apache.ignite.configuration.DataRegionConfiguration;
+import org.apache.ignite.configuration.DataStorageConfiguration;
+import org.apache.ignite.configuration.IgniteConfiguration;
+import org.apache.ignite.configuration.TopologyValidator;
+import org.apache.ignite.internal.IgniteEx;
+import org.apache.ignite.testframework.GridTestUtils;
+import org.apache.ignite.testframework.junits.common.GridCommonAbstractTest;
+import org.apache.ignite.topology.MdcTopologyValidator;
+import org.junit.Test;
+
+/** */
+public class MdcTopologyValidatorTest extends GridCommonAbstractTest {
+    /** */
+    private static final String DC_ID_0 = "DC0";
+
+    /** */
+    private static final String DC_ID_1 = "DC1";
+
+    /** */
+    private static final String DC_ID_2 = "DC2";
+
+    /** */
+    private static final String KEY = "key";
+
+    /** */
+    private static final String VAL = "val";
+
+    /** {@inheritDoc} */
+    @Override protected void afterTest() throws Exception {
+        super.afterTest();
+
+        stopAllGrids();
+
+        cleanPersistenceDir();
+
+        System.clearProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID);
+    }
+
+    /** {@inheritDoc} */
+    @Override protected IgniteConfiguration getConfiguration(String 
igniteInstanceName) throws Exception {
+        return super.getConfiguration(igniteInstanceName)
+            .setDataStorageConfiguration(
+                new DataStorageConfiguration()
+                    .setDefaultDataRegionConfiguration(
+                        new DataRegionConfiguration()
+                            .setPersistenceEnabled(true)
+                    )
+            )
+            .setConsistentId(igniteInstanceName);
+    }
+
+    /** */
+    @Test
+    public void testEmptyConfig() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Missing datacenters or main datacenter");
+    }
+
+    /** */
+    @Test
+    public void testOddDcsWithMain() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1, DC_ID_2));
+        topValidator.setMainDatacenter(DC_ID_1);
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Datacenters count must be even when main datacenter is set.");
+    }
+
+    /** Checks 1DC case with MdcTopologyValidator usage.*/
+    @Test
+    public void testEmptyDc() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of());
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Missing datacenters");
+    }
+
+    /** */
+    @Test
+    public void testNodeWitoutDCWithMajority() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1, DC_ID_2));
+
+        IgniteEx srv = startGrid(0);
+
+        waitForTopology(1);
+
+        srv.cluster().state(ClusterState.ACTIVE);
+
+        CacheConfiguration<Object, Object> cfgCache = new 
CacheConfiguration<>("cache").setTopologyValidator(topValidator);
+
+        IgniteCache cache = srv.createCache(cfgCache);
+
+        GridTestUtils.assertThrows(log, () -> cache.put(KEY, VAL), 
IgniteException.class, "cache topology is not valid");
+    }
+
+    /** */
+    @Test
+    public void testNodeWitoutDCWithMain() throws Exception {

Review Comment:
   ```suggestion
       public void testNodeWithoutDcSpecifiedWithMainBasedValidator() throws 
Exception {
   ```



##########
modules/core/src/test/java/org/apache/ignite/spi/failover/topology/validator/MdcTopologyValidatorTest.java:
##########
@@ -0,0 +1,333 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.ignite.spi.failover.topology.validator;
+
+import java.util.Set;
+import java.util.concurrent.ThreadLocalRandom;
+import javax.cache.CacheException;
+import org.apache.ignite.IgniteCache;
+import org.apache.ignite.IgniteCheckedException;
+import org.apache.ignite.IgniteException;
+import org.apache.ignite.IgniteSystemProperties;
+import org.apache.ignite.cluster.ClusterState;
+import org.apache.ignite.configuration.CacheConfiguration;
+import org.apache.ignite.configuration.DataRegionConfiguration;
+import org.apache.ignite.configuration.DataStorageConfiguration;
+import org.apache.ignite.configuration.IgniteConfiguration;
+import org.apache.ignite.configuration.TopologyValidator;
+import org.apache.ignite.internal.IgniteEx;
+import org.apache.ignite.testframework.GridTestUtils;
+import org.apache.ignite.testframework.junits.common.GridCommonAbstractTest;
+import org.apache.ignite.topology.MdcTopologyValidator;
+import org.junit.Test;
+
+/** */
+public class MdcTopologyValidatorTest extends GridCommonAbstractTest {
+    /** */
+    private static final String DC_ID_0 = "DC0";
+
+    /** */
+    private static final String DC_ID_1 = "DC1";
+
+    /** */
+    private static final String DC_ID_2 = "DC2";
+
+    /** */
+    private static final String KEY = "key";
+
+    /** */
+    private static final String VAL = "val";
+
+    /** {@inheritDoc} */
+    @Override protected void afterTest() throws Exception {
+        super.afterTest();
+
+        stopAllGrids();
+
+        cleanPersistenceDir();
+
+        System.clearProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID);
+    }
+
+    /** {@inheritDoc} */
+    @Override protected IgniteConfiguration getConfiguration(String 
igniteInstanceName) throws Exception {
+        return super.getConfiguration(igniteInstanceName)
+            .setDataStorageConfiguration(
+                new DataStorageConfiguration()
+                    .setDefaultDataRegionConfiguration(
+                        new DataRegionConfiguration()
+                            .setPersistenceEnabled(true)
+                    )
+            )
+            .setConsistentId(igniteInstanceName);
+    }
+
+    /** */
+    @Test
+    public void testEmptyConfig() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Missing datacenters or main datacenter");
+    }
+
+    /** */
+    @Test
+    public void testOddDcsWithMain() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1, DC_ID_2));
+        topValidator.setMainDatacenter(DC_ID_1);
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Datacenters count must be even when main datacenter is set.");
+    }
+
+    /** Checks 1DC case with MdcTopologyValidator usage.*/
+    @Test
+    public void testEmptyDc() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of());
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Missing datacenters");
+    }
+
+    /** */
+    @Test
+    public void testNodeWitoutDCWithMajority() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1, DC_ID_2));
+
+        IgniteEx srv = startGrid(0);
+
+        waitForTopology(1);
+
+        srv.cluster().state(ClusterState.ACTIVE);
+
+        CacheConfiguration<Object, Object> cfgCache = new 
CacheConfiguration<>("cache").setTopologyValidator(topValidator);
+
+        IgniteCache cache = srv.createCache(cfgCache);
+
+        GridTestUtils.assertThrows(log, () -> cache.put(KEY, VAL), 
IgniteException.class, "cache topology is not valid");
+    }
+
+    /** */
+    @Test
+    public void testNodeWitoutDCWithMain() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setMainDatacenter(DC_ID_1);
+
+        IgniteEx srv = startGrid(0);
+
+        waitForTopology(1);
+
+        srv.cluster().state(ClusterState.ACTIVE);
+
+        CacheConfiguration<Object, Object> cfgCache = new 
CacheConfiguration<>("cache").setTopologyValidator(topValidator);
+
+        IgniteCache cache = srv.createCache(cfgCache);
+
+        GridTestUtils.assertThrows(log, () -> cache.put(KEY, VAL), 
IgniteException.class, "cache topology is not valid");
+    }
+
+    /** */
+    @Test
+    public void testClientDoesNotAffectValidation() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setMainDatacenter(DC_ID_1);
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1));
+
+        System.setProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID, 
DC_ID_0);
+        startGrid(0);
+
+        System.setProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID, 
DC_ID_1);
+        IgniteEx client = startClientGrid("client");
+
+        waitForTopology(2);
+
+        client.cluster().state(ClusterState.ACTIVE);
+
+        CacheConfiguration<Object, Object> cfgCache = new 
CacheConfiguration<>("cache").setTopologyValidator(topValidator);
+
+        IgniteCache<Object, Object> cache = client.getOrCreateCache(cfgCache);
+
+        GridTestUtils.assertThrows(log, () -> cache.put(KEY, VAL), 
IgniteException.class, "cache topology is not valid");
+    }
+
+    /** */
+    @Test
+    public void testTopologyValidatorEqualityCheck() throws Exception {
+        System.setProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID, 
DC_ID_1);
+        IgniteEx srv0 = startGrid(0);
+
+        startGrid(1);
+
+        waitForTopology(2);
+
+        srv0.cluster().state(ClusterState.ACTIVE);
+
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setMainDatacenter(DC_ID_1);
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1));
+
+        CacheConfiguration<Object, Object> cfgCache1 = new 
CacheConfiguration<>(DEFAULT_CACHE_NAME).setTopologyValidator(topValidator);
+
+        srv0.getOrCreateCache(cfgCache1);
+
+        stopGrid(1);
+
+        srv0.destroyCache(cfgCache1.getName());
+
+        topValidator.setMainDatacenter(DC_ID_0); // Changed
+
+        CacheConfiguration<Object, Object> cfgCache2 = new 
CacheConfiguration<>(DEFAULT_CACHE_NAME).setTopologyValidator(topValidator);
+
+        srv0.getOrCreateCache(cfgCache2);
+
+        startGrid(2);
+
+        waitForTopology(2);
+
+        GridTestUtils.assertThrows(log, () -> startGrid(1), 
IgniteCheckedException.class, "Cache topology validator mismatch");
+    }
+
+    /** */
+    @Test
+    public void testMainDc() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1, DC_ID_2, "DC4"));
+        topValidator.setMainDatacenter(DC_ID_1);
+
+        IgniteCache<Object, Object> cache = 
createClusterWithCache(topValidator, true);
+
+        cache.put(KEY, VAL);
+        assertEquals(VAL, cache.get(KEY));
+
+        stopGrid(2);
+
+        cache.put(KEY, VAL + 1);
+        assertEquals(VAL + 1, cache.get(KEY));
+
+        stopGrid(1);
+
+        GridTestUtils.assertThrows(log, () -> cache.put(KEY, VAL + 2), 
IgniteException.class, "cache topology is not valid");
+    }
+
+    /** */
+    @Test
+    public void testMajority() throws Exception {

Review Comment:
   ```suggestion
       public void testMajorityBasedValidator() throws Exception {
   ```



##########
modules/core/src/test/java/org/apache/ignite/spi/failover/topology/validator/MdcTopologyValidatorTest.java:
##########
@@ -0,0 +1,333 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.ignite.spi.failover.topology.validator;
+
+import java.util.Set;
+import java.util.concurrent.ThreadLocalRandom;
+import javax.cache.CacheException;
+import org.apache.ignite.IgniteCache;
+import org.apache.ignite.IgniteCheckedException;
+import org.apache.ignite.IgniteException;
+import org.apache.ignite.IgniteSystemProperties;
+import org.apache.ignite.cluster.ClusterState;
+import org.apache.ignite.configuration.CacheConfiguration;
+import org.apache.ignite.configuration.DataRegionConfiguration;
+import org.apache.ignite.configuration.DataStorageConfiguration;
+import org.apache.ignite.configuration.IgniteConfiguration;
+import org.apache.ignite.configuration.TopologyValidator;
+import org.apache.ignite.internal.IgniteEx;
+import org.apache.ignite.testframework.GridTestUtils;
+import org.apache.ignite.testframework.junits.common.GridCommonAbstractTest;
+import org.apache.ignite.topology.MdcTopologyValidator;
+import org.junit.Test;
+
+/** */
+public class MdcTopologyValidatorTest extends GridCommonAbstractTest {
+    /** */
+    private static final String DC_ID_0 = "DC0";
+
+    /** */
+    private static final String DC_ID_1 = "DC1";
+
+    /** */
+    private static final String DC_ID_2 = "DC2";
+
+    /** */
+    private static final String KEY = "key";
+
+    /** */
+    private static final String VAL = "val";
+
+    /** {@inheritDoc} */
+    @Override protected void afterTest() throws Exception {
+        super.afterTest();
+
+        stopAllGrids();
+
+        cleanPersistenceDir();
+
+        System.clearProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID);
+    }
+
+    /** {@inheritDoc} */
+    @Override protected IgniteConfiguration getConfiguration(String 
igniteInstanceName) throws Exception {
+        return super.getConfiguration(igniteInstanceName)
+            .setDataStorageConfiguration(
+                new DataStorageConfiguration()
+                    .setDefaultDataRegionConfiguration(
+                        new DataRegionConfiguration()
+                            .setPersistenceEnabled(true)
+                    )
+            )
+            .setConsistentId(igniteInstanceName);
+    }
+
+    /** */
+    @Test
+    public void testEmptyConfig() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Missing datacenters or main datacenter");
+    }
+
+    /** */
+    @Test
+    public void testOddDcsWithMain() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1, DC_ID_2));
+        topValidator.setMainDatacenter(DC_ID_1);
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Datacenters count must be even when main datacenter is set.");
+    }
+
+    /** Checks 1DC case with MdcTopologyValidator usage.*/
+    @Test
+    public void testEmptyDc() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of());
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Missing datacenters");
+    }
+
+    /** */
+    @Test
+    public void testNodeWitoutDCWithMajority() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1, DC_ID_2));
+
+        IgniteEx srv = startGrid(0);
+
+        waitForTopology(1);
+
+        srv.cluster().state(ClusterState.ACTIVE);
+
+        CacheConfiguration<Object, Object> cfgCache = new 
CacheConfiguration<>("cache").setTopologyValidator(topValidator);
+
+        IgniteCache cache = srv.createCache(cfgCache);
+
+        GridTestUtils.assertThrows(log, () -> cache.put(KEY, VAL), 
IgniteException.class, "cache topology is not valid");
+    }
+
+    /** */
+    @Test
+    public void testNodeWitoutDCWithMain() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setMainDatacenter(DC_ID_1);
+
+        IgniteEx srv = startGrid(0);
+
+        waitForTopology(1);
+
+        srv.cluster().state(ClusterState.ACTIVE);
+
+        CacheConfiguration<Object, Object> cfgCache = new 
CacheConfiguration<>("cache").setTopologyValidator(topValidator);
+
+        IgniteCache cache = srv.createCache(cfgCache);
+
+        GridTestUtils.assertThrows(log, () -> cache.put(KEY, VAL), 
IgniteException.class, "cache topology is not valid");
+    }
+
+    /** */
+    @Test
+    public void testClientDoesNotAffectValidation() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setMainDatacenter(DC_ID_1);
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1));
+
+        System.setProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID, 
DC_ID_0);
+        startGrid(0);
+
+        System.setProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID, 
DC_ID_1);
+        IgniteEx client = startClientGrid("client");
+
+        waitForTopology(2);
+
+        client.cluster().state(ClusterState.ACTIVE);
+
+        CacheConfiguration<Object, Object> cfgCache = new 
CacheConfiguration<>("cache").setTopologyValidator(topValidator);
+
+        IgniteCache<Object, Object> cache = client.getOrCreateCache(cfgCache);
+
+        GridTestUtils.assertThrows(log, () -> cache.put(KEY, VAL), 
IgniteException.class, "cache topology is not valid");
+    }
+
+    /** */
+    @Test
+    public void testTopologyValidatorEqualityCheck() throws Exception {
+        System.setProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID, 
DC_ID_1);
+        IgniteEx srv0 = startGrid(0);
+
+        startGrid(1);
+
+        waitForTopology(2);
+
+        srv0.cluster().state(ClusterState.ACTIVE);
+
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setMainDatacenter(DC_ID_1);
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1));
+
+        CacheConfiguration<Object, Object> cfgCache1 = new 
CacheConfiguration<>(DEFAULT_CACHE_NAME).setTopologyValidator(topValidator);
+
+        srv0.getOrCreateCache(cfgCache1);
+
+        stopGrid(1);
+
+        srv0.destroyCache(cfgCache1.getName());
+
+        topValidator.setMainDatacenter(DC_ID_0); // Changed
+
+        CacheConfiguration<Object, Object> cfgCache2 = new 
CacheConfiguration<>(DEFAULT_CACHE_NAME).setTopologyValidator(topValidator);
+
+        srv0.getOrCreateCache(cfgCache2);
+
+        startGrid(2);
+
+        waitForTopology(2);
+
+        GridTestUtils.assertThrows(log, () -> startGrid(1), 
IgniteCheckedException.class, "Cache topology validator mismatch");
+    }
+
+    /** */
+    @Test
+    public void testMainDc() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1, DC_ID_2, "DC4"));
+        topValidator.setMainDatacenter(DC_ID_1);
+
+        IgniteCache<Object, Object> cache = 
createClusterWithCache(topValidator, true);
+
+        cache.put(KEY, VAL);
+        assertEquals(VAL, cache.get(KEY));
+
+        stopGrid(2);
+
+        cache.put(KEY, VAL + 1);
+        assertEquals(VAL + 1, cache.get(KEY));
+
+        stopGrid(1);
+
+        GridTestUtils.assertThrows(log, () -> cache.put(KEY, VAL + 2), 
IgniteException.class, "cache topology is not valid");
+    }
+
+    /** */
+    @Test
+    public void testMajority() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1, DC_ID_2));
+
+        IgniteCache<Object, Object> cache = 
createClusterWithCache(topValidator, true);
+
+        cache.put(KEY, VAL);
+        assertEquals(VAL, cache.get(KEY));
+
+        int randomNode = ThreadLocalRandom.current().nextInt(1, 3);
+
+        stopGrid(randomNode);
+
+        cache.put(KEY, VAL + 1);
+        assertEquals(VAL + 1, cache.get(KEY));
+
+        stopGrid(randomNode == 1 ? 2 : 1);
+
+        GridTestUtils.assertThrows(log, () -> cache.put(KEY, VAL + 2), 
IgniteException.class, "cache topology is not valid");
+    }
+
+    /** */
+    @Test
+    public void testBigCluster() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1, DC_ID_2));
+
+        System.setProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID, 
DC_ID_0);
+
+        startGrid(0);
+
+        System.setProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID, 
DC_ID_1);
+
+        IgniteEx srv = startGrid(1);
+        startGrid(10);
+        startGrid(11);
+        startGrid(12);
+
+        System.setProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID, 
DC_ID_2);
+
+        startGrid(2);
+
+        waitForTopology(6);
+
+        srv.cluster().state(ClusterState.ACTIVE);
+
+        CacheConfiguration<Object, Object> cfgCache = new 
CacheConfiguration<>("cache").setTopologyValidator(topValidator);
+
+        IgniteCache<Object, Object> cache = srv.createCache(cfgCache);
+
+        cache.put(KEY, VAL);
+        assertEquals(VAL, cache.get(KEY));
+
+        stopGrid(0);
+        stopGrid(2);
+
+        // Checking case when 4 nodes are alive, but only at single DC

Review Comment:
   ```suggestion
           // Checking case when 4 nodes are alive, but only in single DC
   ```



##########
modules/core/src/test/java/org/apache/ignite/spi/failover/topology/validator/MdcTopologyValidatorTest.java:
##########
@@ -0,0 +1,333 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.ignite.spi.failover.topology.validator;
+
+import java.util.Set;
+import java.util.concurrent.ThreadLocalRandom;
+import javax.cache.CacheException;
+import org.apache.ignite.IgniteCache;
+import org.apache.ignite.IgniteCheckedException;
+import org.apache.ignite.IgniteException;
+import org.apache.ignite.IgniteSystemProperties;
+import org.apache.ignite.cluster.ClusterState;
+import org.apache.ignite.configuration.CacheConfiguration;
+import org.apache.ignite.configuration.DataRegionConfiguration;
+import org.apache.ignite.configuration.DataStorageConfiguration;
+import org.apache.ignite.configuration.IgniteConfiguration;
+import org.apache.ignite.configuration.TopologyValidator;
+import org.apache.ignite.internal.IgniteEx;
+import org.apache.ignite.testframework.GridTestUtils;
+import org.apache.ignite.testframework.junits.common.GridCommonAbstractTest;
+import org.apache.ignite.topology.MdcTopologyValidator;
+import org.junit.Test;
+
+/** */
+public class MdcTopologyValidatorTest extends GridCommonAbstractTest {
+    /** */
+    private static final String DC_ID_0 = "DC0";
+
+    /** */
+    private static final String DC_ID_1 = "DC1";
+
+    /** */
+    private static final String DC_ID_2 = "DC2";
+
+    /** */
+    private static final String KEY = "key";
+
+    /** */
+    private static final String VAL = "val";
+
+    /** {@inheritDoc} */
+    @Override protected void afterTest() throws Exception {
+        super.afterTest();
+
+        stopAllGrids();
+
+        cleanPersistenceDir();
+
+        System.clearProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID);
+    }
+
+    /** {@inheritDoc} */
+    @Override protected IgniteConfiguration getConfiguration(String 
igniteInstanceName) throws Exception {
+        return super.getConfiguration(igniteInstanceName)
+            .setDataStorageConfiguration(
+                new DataStorageConfiguration()
+                    .setDefaultDataRegionConfiguration(
+                        new DataRegionConfiguration()
+                            .setPersistenceEnabled(true)
+                    )
+            )
+            .setConsistentId(igniteInstanceName);
+    }
+
+    /** */
+    @Test
+    public void testEmptyConfig() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Missing datacenters or main datacenter");
+    }
+
+    /** */
+    @Test
+    public void testOddDcsWithMain() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1, DC_ID_2));
+        topValidator.setMainDatacenter(DC_ID_1);
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Datacenters count must be even when main datacenter is set.");
+    }
+
+    /** Checks 1DC case with MdcTopologyValidator usage.*/
+    @Test
+    public void testEmptyDc() {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of());
+
+        GridTestUtils.assertThrows(log,
+            () -> createClusterWithCache(topValidator, false),
+            CacheException.class,
+            "Missing datacenters");
+    }
+
+    /** */
+    @Test
+    public void testNodeWitoutDCWithMajority() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1, DC_ID_2));
+
+        IgniteEx srv = startGrid(0);
+
+        waitForTopology(1);
+
+        srv.cluster().state(ClusterState.ACTIVE);
+
+        CacheConfiguration<Object, Object> cfgCache = new 
CacheConfiguration<>("cache").setTopologyValidator(topValidator);
+
+        IgniteCache cache = srv.createCache(cfgCache);
+
+        GridTestUtils.assertThrows(log, () -> cache.put(KEY, VAL), 
IgniteException.class, "cache topology is not valid");
+    }
+
+    /** */
+    @Test
+    public void testNodeWitoutDCWithMain() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setMainDatacenter(DC_ID_1);
+
+        IgniteEx srv = startGrid(0);
+
+        waitForTopology(1);
+
+        srv.cluster().state(ClusterState.ACTIVE);
+
+        CacheConfiguration<Object, Object> cfgCache = new 
CacheConfiguration<>("cache").setTopologyValidator(topValidator);
+
+        IgniteCache cache = srv.createCache(cfgCache);
+
+        GridTestUtils.assertThrows(log, () -> cache.put(KEY, VAL), 
IgniteException.class, "cache topology is not valid");
+    }
+
+    /** */
+    @Test
+    public void testClientDoesNotAffectValidation() throws Exception {
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setMainDatacenter(DC_ID_1);
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1));
+
+        System.setProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID, 
DC_ID_0);
+        startGrid(0);
+
+        System.setProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID, 
DC_ID_1);
+        IgniteEx client = startClientGrid("client");
+
+        waitForTopology(2);
+
+        client.cluster().state(ClusterState.ACTIVE);
+
+        CacheConfiguration<Object, Object> cfgCache = new 
CacheConfiguration<>("cache").setTopologyValidator(topValidator);
+
+        IgniteCache<Object, Object> cache = client.getOrCreateCache(cfgCache);
+
+        GridTestUtils.assertThrows(log, () -> cache.put(KEY, VAL), 
IgniteException.class, "cache topology is not valid");
+    }
+
+    /** */
+    @Test
+    public void testTopologyValidatorEqualityCheck() throws Exception {
+        System.setProperty(IgniteSystemProperties.IGNITE_DATA_CENTER_ID, 
DC_ID_1);
+        IgniteEx srv0 = startGrid(0);
+
+        startGrid(1);
+
+        waitForTopology(2);
+
+        srv0.cluster().state(ClusterState.ACTIVE);
+
+        MdcTopologyValidator topValidator = new MdcTopologyValidator();
+
+        topValidator.setMainDatacenter(DC_ID_1);
+        topValidator.setDatacenters(Set.of(DC_ID_0, DC_ID_1));
+
+        CacheConfiguration<Object, Object> cfgCache1 = new 
CacheConfiguration<>(DEFAULT_CACHE_NAME).setTopologyValidator(topValidator);
+
+        srv0.getOrCreateCache(cfgCache1);
+
+        stopGrid(1);
+
+        srv0.destroyCache(cfgCache1.getName());
+
+        topValidator.setMainDatacenter(DC_ID_0); // Changed
+
+        CacheConfiguration<Object, Object> cfgCache2 = new 
CacheConfiguration<>(DEFAULT_CACHE_NAME).setTopologyValidator(topValidator);
+
+        srv0.getOrCreateCache(cfgCache2);
+
+        startGrid(2);
+
+        waitForTopology(2);
+
+        GridTestUtils.assertThrows(log, () -> startGrid(1), 
IgniteCheckedException.class, "Cache topology validator mismatch");
+    }
+
+    /** */
+    @Test
+    public void testMainDc() throws Exception {

Review Comment:
   ```suggestion
       public void testMainDcBasedValidator() throws Exception {
   ```



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