[KAFKA-7755] Kubernetes - Kafka clients are resolving DNS entries only one time

• Type: Bug
• Status: Resolved
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 2.1.0
• Fix Version/s: 2.2.0, 2.1.1
• Component/s: clients
• Environment: Kubernetes
• Assignee: Unassigned
• Reporter: Loïc Monney
• Created: 19/Dec/18 07:49
• Updated: 20/Mar/20 17:08
• Resolved: 07/Jan/19 19:23

Description

Introduction
Since 2.1.0 Kafka clients are supporting multiple DNS resolved IP addresses if the first one fails. This change has been introduced by https://issues.apache.org/jira/browse/KAFKA-6863. However this DNS resolution is now performed only one time by the clients. This is not a problem if all brokers have fixed IP addresses, however this is definitely an issue when Kafka brokers are run on top of Kubernetes. Indeed, new Kubernetes pods will receive another IP address, so as soon as all brokers will have been restarted clients won't be able to reconnect to any broker.

Impact
Everyone running Kafka 2.1 or later on top of Kubernetes is impacted when a rolling restart is performed.

Root cause
Since https://issues.apache.org/jira/browse/KAFKA-6863 Kafka clients are resolving DNS entries only once.

Proposed solution
In https://github.com/apache/kafka/blob/trunk/clients/src/main/java/org/apache/kafka/clients/ClusterConnectionStates.java#L368 Kafka clients should perform the DNS resolution again when all IP addresses have been "used" (when index is back to 0)

Issue Links

• is caused by: KAFKA-6863 Kafka clients should try to use multiple DNS resolved IP addresses if the first one fails
• is duplicated by: KAFKA-8057 Producer (and probably consumer) retains IP address of broker instead of resolving
• relates to: KAFKA-7958 Transactions are broken with kubernetes hosted brokers
• links to: GitHub Pull Request #6049