In Kraft mode, if I create a topic, I am occasionally seeing MetadataResponse with a valid leader, and if I immediately produce to that topic, I am seeing NOT_LEADER_FOR_PARTITION. There may be another bug causing Kraft to return a leader in metadata but reject requests to that leader, but this is showing a bigger problem.
Kafka currently accepts produce requests to new partitions with a non-zero sequence number. I have confirmed this locally by modifying my client to start producing with a sequence number of 10. Producing three records sequentially back to back (seq 10, 11, 12) are all successful. I think this comment in the Kafka source also indicates roughly the same thing.
- Client initializes producer ID
- Client creates topic "foo" (for the problem, we will ignore partitions – there is just one partition)
- Client sends produce request A with 5 records
- Client sends produce request B with 5 records before receiving a response for A
- Broker returns NOT_LEADER_FOR_PARTITION to produce request A
- Broker finally initializes, becomes leader before seeing request B
- Broker accepts request B as the first request
- Broker believes sequence number 5 is ok, and is expecting the next sequence to be 10
- Client retries requests A and B, because A failed
- Broker sees request A with sequence 0, returns OutOfOrderSequenceException
- Client enters a fatal state, because OOOSN is not retryable
I can reliably reproduce this error using Kraft mode with 1 broker. I am using the following docker compose:
# Set this to "PLAINTEXT://127.0.0.1:9092" if you want to run this container on localhost via Docker
KAFKA_KRAFT_CLUSTER_ID: XkpGZQ27R3eTl3OdTm2LYA # 16 byte base64-encoded UUID
BITNAMI_DEBUG: true # Enable this to get more info on startup failures
I am running the franz-go integration tests to trigger this (frequently, but not all of the time). However, these tests are not required. The behavior described above can occasionally reproduce this.
I have never experienced this against the zookeeper version. It seems that the zk version always fully initializes a topic immediately and does not return NOT_LEADER_FOR_PARTITION on the first produce request. This is a separate problem – but the main problem described above exists in all versions, and can be experienced in zk in very strange circumstances.