sashapolo commented on code in PR #722:
URL: https://github.com/apache/ignite-3/pull/722#discussion_r845238134


##########
modules/cluster-management/src/main/java/org/apache/ignite/internal/cluster/management/ClusterManagementGroupManager.java:
##########
@@ -133,90 +138,377 @@ public void initCluster(Collection<String> 
metaStorageNodeNames, Collection<Stri
         } catch (InterruptedException e) {
             Thread.currentThread().interrupt();
 
-            throw new IgniteInternalException("Interrupted while initializing 
the cluster", e);
+            throw new InitException("Interrupted while initializing the 
cluster", e);
         } catch (ExecutionException e) {
-            throw new IgniteInternalException("Unable to initialize the 
cluster", e.getCause());
+            throw new InitException("Unable to initialize the cluster", 
e.getCause());
         } finally {
             busyLock.leaveBusy();
         }
     }
 
-    private void handleInit(CmgInitMessage msg, NetworkAddress addr, long 
correlationId) throws NodeStoppingException {
-        List<ClusterNode> nodes = resolveNodes(clusterService, msg.cmgNodes());
+    @Override
+    public void start() {
+        var messageHandlerFactory = new CmgMessageHandlerFactory(busyLock, 
msgFactory, clusterService);
+
+        // register the ClusterState handler first, because local state 
recovery might send such messages
+        clusterService.messagingService().addMessageHandler(
+                CmgMessageGroup.class,
+                messageHandlerFactory.wrapHandler((message, senderAddr, 
correlationId) -> {
+                    if (message instanceof ClusterStateMessage) {
+                        assert correlationId != null;
 
-        raftManager.prepareRaftGroup(CMG_RAFT_GROUP_NAME, nodes, 
CmgRaftGroupListener::new)
-                .whenComplete((service, e) -> {
-                    MessagingService messagingService = 
clusterService.messagingService();
+                        handleClusterState((ClusterStateMessage) message, 
senderAddr, correlationId);
+                    }
+                })
+        );
 
-                    if (e == null) {
-                        ClusterNode leader = getLeader(service);
+        raftService = recoverLocalState();
 
-                        ClusterNode thisNode = 
clusterService.topologyService().localMember();
+        // register the Init handler second in order to handle the command 
differently, depending on the local state
+        clusterService.messagingService().addMessageHandler(
+                CmgMessageGroup.class,
+                messageHandlerFactory.wrapHandler((message, senderAddr, 
correlationId) -> {
+                    if (message instanceof CancelInitMessage) {
+                        handleCancelInit((CancelInitMessage) message);
+                    } else if (message instanceof CmgInitMessage) {
+                        assert correlationId != null;
 
-                        messagingService.respond(addr, 
successResponse(msgFactory), correlationId);
+                        handleInit((CmgInitMessage) message, senderAddr, 
correlationId);
+                    }
+                })
+        );
 
-                        if (leader.equals(thisNode)) {
-                            broadcastClusterState(msg.metaStorageNodes());
+        restComponent.registerHandlers(routes ->
+                routes.post(REST_ENDPOINT, APPLICATION_JSON.toString(), new 
InitCommandHandler(clusterInitializer))
+        );
+    }
+
+    /**
+     * Extracts the local state (if any) and starts the CMG.
+     *
+     * @return Future that resolves into the CMG Raft service or {@code null} 
the local state is empty.
+     */
+    @Nullable
+    private CompletableFuture<CmgRaftService> recoverLocalState() {
+        Collection<String> cmgNodes;
+
+        try {
+            cmgNodes = localStateStorage.cmgNodeNames().get();
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+
+            throw new IgniteInternalException("Interrupted while retrieving 
local CMG state", e);
+        } catch (ExecutionException e) {
+            throw new IgniteInternalException("Error while retrieving local 
CMG state", e);
+        }
+
+        if (cmgNodes.isEmpty()) {
+            return null;
+        }
+
+        return startCmgRaftService(cmgNodes)
+                .thenCompose(service -> {
+                    log.info("Local CMG state recovered");
+
+                    return service.isCurrentNodeLeader()
+                            .thenCompose(isLeader -> {
+                                if (isLeader) {
+                                    return service.readClusterState()
+                                            // Raft state might not have been 
initialized in case of leader failure during cluster init
+                                            .thenCompose(state -> state == 
null ? completedFuture(null) : onLeaderElected(service, state));
+                                } else {
+                                    return completedFuture(null);
+                                }
+                            })
+                            .thenApply(v -> service);
+                });
+    }
+
+    /**
+     * Handles the Init command.
+     *
+     * <p>This method needs to take the following possibilities into account, 
depending on the local state and the Raft state:
+     * <ol>
+     *     <li>No local state found - this means that the current node has 
never been initialized before.</li>
+     *     <li>Local state found, but no CMG state present in the Raft storage 
- this means that the node has failed somewhere during
+     *     the init process. In this case we need to check the consistency of 
the local state and the received message and complete
+     *     the init process.</li>
+     *     <li>Local state found and CMG state is present in the Raft storage 
- this means that the node has been initialized successfully
+     *     and a user may be retrying the init in case the successful response 
was lost. To make the init message idempotent
+     *     we simply check that the Raft state and the received message are 
the same.</li>
+     * </ol>
+     */
+    private void handleInit(CmgInitMessage msg, NetworkAddress addr, long 
correlationId) {
+        var newState = new ClusterState(msg.cmgNodes(), 
msg.metaStorageNodes());
+
+        CompletableFuture<CmgRaftService> raftService = this.raftService;
+
+        // This future is needed to add a completion listener at the end of 
the method
+        CompletableFuture<?> resultHook;
+
+        if (raftService == null) {
+            // Raft service has not been started
+            log.info("Init command received, starting the CMG: " + newState);
+
+            raftService = initCmgRaftService(newState);
+
+            this.raftService = raftService;
+
+            resultHook = raftService;
+        } else {
+            // Raft service has been started, which means that this node has 
already received an init command at least once, but
+            // we still need to check that the initialization has completed 
successfully.
+            log.info("Init command received, but the CMG has already been 
started");
+
+            resultHook = raftService.thenCompose(service ->
+                    service.readClusterState()
+                            .thenCompose(state -> {
+                                if (state == null) {
+                                    // Raft state is empty, perform 
re-initialization
+                                    log.info("CMG state is missing, completing 
initialization");
+
+                                    if 
(service.nodeNames().equals(newState.cmgNodes())) {
+                                        return service.isCurrentNodeLeader()
+                                                
.thenCompose(isCurrentNodeLeader ->
+                                                        isCurrentNodeLeader ? 
initCmgState(service, newState) : completedFuture(null));
+                                    } else {
+                                        throw new 
IllegalStateException(String.format(

Review Comment:
   This is how the design document described this situation: if an init command 
fails, it should be re-tried with the same parameters. I guess this is needed 
to avoid complicated race conditions.



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