[KAFKA-12664] Mirrormaker 2.0 infinite rebalance loop when dealing with more than 2 clusters in standalone mode

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Not A Bug
• Affects Version/s: 2.5.0, 2.4.1, 2.6.0, 2.7.0
• Component/s: mirrormaker
• Assignee: Daniel Urban
• Reporter: Edward Vaisman
• Created: 13/Apr/21 18:10
• Updated: 14/Apr/21 15:29
• Resolved: 14/Apr/21 15:29

Description

Hi Folks, I came across this issue when trying to aggregate data from two separate data centres into one data centre.

In the configuration below, you can see I am trying to replicate a topic from dc1 (named test_topic_dc1) to dc3 as well as replicate a topic from dc2 (test_topic_dc2) to dc3.

However, when I try to replicate both topics from those datacenters at the same time I notice that connect gets stuck in a rebalance loop (see attachment for logs)
connect.log.tar.gz

excerpt of connect.log

2021-04-13 17:03:06,360] INFO [Worker clientId=connect-3, groupId=mm2-dc2] Successfully synced group in generation Generation{generationId=347, memberId='connect-3-c59342c3-ca62-41cc-964c-41a0f98351c0', protocol='sessioned'} (org.apache.kafka.clients.consumer.internals.AbstractCoordinator:756)[2021-04-13 17:03:06,360] INFO [Worker clientId=connect-4, groupId=mm2-dc2] Rebalance started (org.apache.kafka.connect.runtime.distributed.WorkerCoordinator:225)[2021-04-13 17:03:06,362] INFO [Worker clientId=connect-4, groupId=mm2-dc2] (Re-)joining group (org.apache.kafka.clients.consumer.internals.AbstractCoordinator:540)[2021-04-13 17:03:06,368] INFO [Worker clientId=connect-2, groupId=mm2-dc3] Rebalance started (org.apache.kafka.connect.runtime.distributed.WorkerCoordinator:225)[2021-04-13 17:03:06,369] INFO [Worker clientId=connect-2, groupId=mm2-dc3] (Re-)joining group (org.apache.kafka.clients.consumer.internals.AbstractCoordinator:540)[2021-04-13 17:03:06,370] INFO [Worker clientId=connect-3, groupId=mm2-dc2] Joined group at generation 347 with protocol version 2 and got assignment: Assignment{error=1, leader='connect-3-c59342c3-ca62-41cc-964c-41a0f98351c0', leaderUrl='NOTUSED/dc1', offset=13, connectorIds=[MirrorSourceConnector], taskIds=[], revokedConnectorIds=[], revokedTaskIds=[], delay=0} with rebalance delay: 0 (org.apache.kafka.connect.runtime.distributed.DistributedHerder:1688)

To replicate the issue here is what I used:

mm2.properties

clusters = dc1, dc2, dc3
dc1.bootstrap.servers = kafka-dc1:19092
dc2.bootstrap.servers = kafka-dc2:19093
dc3.bootstrap.servers = kafka-dc3:19094
dc1.group.id=mm2-dc1
dc2.group.id=mm2-dc2
dc3.group.id=mm2-dc3
replication.factor=1
checkpoints.topic.replication.factor=1
heartbeats.topic.replication.factor=1
offset-syncs.topic.replication.factor=1
offset.storage.replication.factor=1
status.storage.replication.factor=1
config.storage.replication.factor=1
dc1->dc3.enabled = true
dc1->dc3.topics = test_topic_dc1
dc2->dc3.enabled = true
dc2->dc3.topics = test_topic_dc2
dc3->dc2 = falsedc3->dc1 = false

This docker-compose-multi.yml file to create local kafka clusters (dc1,dc2,dc3)
(I set docker to use 6 cpus, 8gb mem, swap 2gb)

I then ran an interactive shell to run mirror maker within the same docker-compose network (change network to match yours)

docker run --network kafka-examples_default -it wurstmeister/kafka:latest bash

# Upload mm2 properties on server

/opt/kafka/bin/connect-mirror-maker.sh mm2.properties

Kafkacat commands to produce to dc1, dc2

kafkacat -b localhost:9092 -t test_topic_dc1 -P
Hello World from DC1!

kafkacat -b localhost:9093 -t test_topic_dc2 -P
Hello World from DC2

I then tried to remove one of the datacenters to confirm if it was a configuration problem, however mirror maker ran successfully with the below configuration

mm2.properties

clusters = dc2, dc3
dc2.bootstrap.servers = kafka-dc2:19093
dc3.bootstrap.servers = kafka-dc3:19094
dc2.group.id=mm2-dc2
dc3.group.id=mm2-dc3
replication.factor=1
checkpoints.topic.replication.factor=1
heartbeats.topic.replication.factor=1
offset-syncs.topic.replication.factor=1
offset.storage.replication.factor=1
status.storage.replication.factor=1
config.storage.replication.factor=1
dc2->dc3.enabled = true
dc2->dc3.topics = test_topic_dc2

Any help would be appreciated!