[FLINK-4660] HadoopFileSystem (with S3A) may leak connections, which cause job to stuck in a restarting loop

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Fix Version/s: 1.3.2, 1.4.0
• Component/s: Runtime / State Backends
• Release Note: Closing the reopened issue to update versions in which this is fixed
• Assignee: Unassigned
• Reporter: Zhenzhong Xu
• Created: 21/Sep/16 19:44
• Updated: 02/Oct/19 17:44
• Resolved: 06/Oct/17 17:03

Description

Flink job with checkpoints enabled and configured to use S3A file system backend, sometimes experiences checkpointing failure due to S3 consistency issue. This behavior is also reported by other people and documented in https://issues.apache.org/jira/browse/FLINK-4218.

This problem gets magnified by current HadoopFileSystem implementation, which can potentially leak S3 client connections, and eventually get into a restarting loop with “Timeout waiting for a connection from pool” exception thrown from aws client.

I looked at the code, seems HadoopFileSystem.java never invoke close() method on fs object upon failure, but the FileSystem may be re-initialized every time the job gets restarted.

A few evidence I observed:
1. When I set the connection pool limit to 128, and below commands shows 128 connections are stuck in CLOSE_WAIT state.

2. task manager logs indicates that state backend file system consistently getting initialized upon job restarting.

3. Log indicates there is NPE during cleanning up of stream task which was caused by “Timeout waiting for connection from pool” exception when trying to create a directory in S3 bucket.
2016-09-02 08:17:50,886 ERROR org.apache.flink.streaming.runtime.tasks.StreamTask - Error during cleanup of stream task
java.lang.NullPointerException
at org.apache.flink.streaming.runtime.tasks.OneInputStreamTask.cleanup(OneInputStreamTask.java:73)
at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:323)
at org.apache.flink.runtime.taskmanager.Task.run(Task.java:589)
at java.lang.Thread.run(Thread.java:745)

4.It appears StreamTask from invoking checkpointing operation, to handling failure, there is no logic associated with closing Hadoop File System object (which internally includes S3 aws client object), which resides in HadoopFileSystem.java.

Issue Links

• relates to: FLINK-4218 Sporadic "java.lang.RuntimeException: Error triggering a checkpoint..." causes task restarting