[ZOOKEEPER-4360] Avoid NPE during metrics execution if the leader is not set on a FOLLOWER node

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.6.2
• Fix Version/s: 3.8.0, 3.7.1, 3.6.4
• Component/s: metric system
• Labels: metrics pull-request-available
• Assignee: Unassigned
• Reporter: Nicoló Boschi
• Created: 30/Aug/21 09:49
• Updated: 09/Oct/23 11:20
• Resolved: 02/Sep/21 16:51

Description

On a follower node, we had this error

ago 20, 2021 1:46:28 PM org.apache.catalina.core.StandardWrapperValve invoke
GRAVE: Servlet.service() for servlet [metrics] in context with path [/metrics] threw exception
java.lang.NullPointerException: Cannot invoke "org.apache.zookeeper.server.quorum.Leader.getProposalStats()" because the return value of "org.apache.zookeeper.server.quorum.LeaderZooKeeperServer.getLeader()" is null
        at org.apache.zookeeper.server.quorum.LeaderZooKeeperServer.lambda$registerMetrics$5(LeaderZooKeeperServer.java:122)
        at magnews.zookeeper.ZooKeeperMetricsProviderAdapter$MetricsContextImpl.lambda$registerGauge$0(ZooKeeperMetricsProviderAdapter.java:91)

Unfortunately, I'm not able to reproduce this error deterministically
 

Issue Links

• links to: GitHub Pull Request #1743