poorbarcode commented on code in PR #23124:
URL: https://github.com/apache/pulsar/pull/23124#discussion_r1717855060
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pip/pip-370.md:
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+# PIP-370: configurable remote topic creation in geo-replication
+
+# Background knowledge
+
+**The current topic creation behavior when enabling Geo-Replication**
+Users using Geo-Replication backup data across multiple clusters, as well as
Admin APIs related to Geo-Replication and internal replicators of brokers, will
trigger topics of auto-creation between clusters.
+- For partitioned topics.
+ - After enabling namespace-level Geo-Replication: the broker will create
topics on the remote cluster automatically when calling `pulsar-admin topics
create-partitioned-topic`. It does not depend on enabling
`allowAutoTopicCreation`.
+ - When enabling topic-level Geo-Replication on a partitioned topic: the
broker will create topics on the remote cluster automatically. It does not
depend on enabling `allowAutoTopicCreation`.
+ - When calling `pulsar-admin topics update-partitioned-topic -p
{partitions}`, the broker will also update partitions on the remote cluster
automatically.
+- For non-partitioned topics and partitions of partitioned topics.
+ - The internal Geo-Replicator will trigger topics auto-creation for remote
clusters. **(Highlight)** It depends on enabling `allowAutoTopicCreation`. In
fact, this behavior is not related to Geo-Replication, it is the behavior of
the internal producer of Geo-Replicator,
+
+# Motivation
+
+In the following scenarios, automatic topic creation across clusters is
problematic due to race conditions during deployments, and there is no choice
that prevents pulsar resource creation affects each other between clusters.
+
+- Users want to maintain pulsar resources manually.
+- Users pulsar resources using `GitOps CD` automated deployment, for which
+ - Clusters are deployed simultaneously without user intervention.
+ - Each cluster is precisely configured from git repo config variables -
including the list of all tenants/namespaces/topics to be created in each
cluster.
+ - Clusters are configured to be exact clones of each other in terms of
pulsar resources.
+
+**Passed solution**: disable `allowAutoTopicCreation`, the APIs `pulsar-admin
topics create-partitioned-topic` still create topics on the remote cluster when
enabled namespace level replication, the API `enable topic-level replication`
still create topics, And the internal replicator will keep printing error logs
due to a not found error.
+
+# Goals
+
+- Introduce a flag to disable the replicators to automatically trigger topic
creation.
+- Move all topic creation/expand-partitions behaviors related to Replication
to the internal Replicator, pulsar admin API that relates to pulsar topics
management does not care about replication anymore.
+ - Move the topic creation operations from `pulsar-admin topics
create-partitioned-topic`, `pulsar-admin topics update-partitioned-topic -p
{partitions}` and `pulsar-admin topics set-replication-clusters` to the
component Replicator in the broker internal.
+
+# Detailed Design
+
+## Configuration
+
+**broker.conf**
+```properties
+# Whether the internal replication of the local cluster will trigger topic
auto-creation on the remote cluster.
+# 1. After enabling namespace-level Geo-Replication: whether the local broker
will create topics on the remote cluster automatically when calling
`pulsar-admin topics create-partitioned-topic`.
+# 2. When enabling topic-level Geo-Replication on a partitioned topic: whether
the local broker will create topics on the remote cluster.
+# 3. Whether the internal Geo-Replicator in the local cluster will trigger
non-persistent topic auto-creation for remote clusters.
+# It is not a dynamic config, the default value is "true" to preserve
backward-compatible behavior.
+createTopicToRemoteClusterForReplication=true
+```
+
+## Design & Implementation Details
+
+### Phase 1: Introduce a flag to disable the replicators to automatically
trigger topic creation.
+- If `createTopicToRemoteClusterForReplication` is set to `false`.
+ 1. After enabling namespace-level Geo-Replication: the broker will not
create topics on the remote cluster automatically when calling `pulsar-admin
topics create-partitioned-topic`.
+ 2. When enabling topic-level Geo-Replication on a partitioned topic: broker
will not create topics on the remote cluster automatically.
+ 3. The internal Geo-Replicator will not trigger topic auto-creation for
remote clusters, it just keeps retrying to check if the topic exists on the
remote cluster, once the topic is created, the replicator starts.
+ 4. It does not change the behavior of creating subscriptions after enabling
`enableReplicatedSubscriptions`, the subscription will also be created on the
remote cluster after users enable. `enableReplicatedSubscriptions`.
+ 5. The config `allowAutoTopicCreation` still works for the local cluster as
before, it will not be affected by the new config
`createTopicToRemoteClusterForReplication`.
+- If `createTopicToRemoteClusterForReplication` is set to `true`.
+ a. All components work as before, see details: `Motivation -> The current
topic creation behavior when enabling Geo-Replication`
+
+### Phase 2: The replicator will check remote topics' partitioned metadata and
update partitions in the remote cluster to the same as the current cluster if
needed.
+- If `createTopicToRemoteClusterForReplication` is set to `false`.
+ - The behavior is the same as Phase 1.
+- If `createTopicToRemoteClusterForReplication` is set to `true`.
+ - When a replicator for a topic partition starts, it checks the partitioned
metadata in the remote cluster first and updates partitions in the remote
cluster to the same as the current cluster if needed. Seem the example as
follows:
+ - `local_cluster.topic.partitions = 2` and the topic does not exist in
the remote cluster: create a partitioned topic with `2` partitions in the
remote cluster.
+ - Before `PIP-370 Phase 2`: the replicator will only trigger partition
creation (`{topic}-partition-0` and `{topic}-partition-1`), and will not care
about partitioned metadata.
+ - `local_cluster.topic.partitions = 2` and
`remote_cluster.topic.partitions = 1`: expand `remote_cluster.topic.partitions`
to `2`.
+ - Before `PIP-370 Phase 2`: the replicator will only trigger partition
creation (`{topic}-partition-0` and `{topic}-partition-1`), and the partitioned
metadata in the remote cluster is still `1`.
+ - `local_cluster.topic.partitions = 2` and
`remote_cluster.topic.partitions >=2 `: modifies nothing.
Review Comment:
For this scenario, it is fine. The messages will be copied to the same
partition in the remote cluster, and no message will be copied to the partition
that is larger than `{local_cluster.topic.partitions}` in the remote cluster
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