[KAFKA-12498] Consumer Group Lag is zero when MirrorMaker 2.0 is running

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.7.0
• Component/s: consumer, replication
• Environment: Kubernetes 1.19.7 ; Strimzi 0.21.1
• Assignee: Unassigned
• Reporter: Olumide Ajiboye
• Created: 18/Mar/21 16:28
• Updated: 18/Mar/21 17:49

Description

I have two Kafka clusters in Active\Passive replication using MM 2.0.
When I produce messages to a topic and try to read from it in the same cluster, the consumer group lag is already set to zero. The replica topic also has the same lag and log-end-offset.
MM2 is using a superuser client and I am using a separate consumer-group with separate credentials and with permission just to read and write to this topic. 
Steps to reproduce:

• Setup cluster and DR cluster with MM2 in uni-directional replication.
• Create a topic.
• Write 10 messages to the topic without any active consumers but with MM2 replicating the topic to a passive Cluster.
• Attempt to read 3 messages from the topic, this creates my consumer group and adds an active consumer. The result is no messages are read

• Describe the consumer group, the result shows Log-End-Offset with correct number of messages, but Lag shows 0

• Attempt to read 3 messages from passive cluster using same consumer-group. Result: no messages consumed, Lag shows 0, Log-End-Offset shows correct number of messages (i.e. same as active cluster)

• Keep consumer running
• Write a few more messages.
• Consumer is now reading latest messages
• Stop consumer
• Keep writing new messages
• Lag shows correct value.

In the absence of MM2, Kafka operation is as expected.