[HDFS-11333] Print a user friendly error message when plugins are not found

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 0.21.0
• Fix Version/s: 2.9.0, 2.7.4, 3.0.0-alpha4, 2.8.2
• Component/s: namenode
• Labels: supportability
• Target Version/s: 2.9.0, 3.0.0-beta1
• Assignee: Wei-Chiu Chuang
• Reporter: Wei-Chiu Chuang
• Created: 11/Jan/17 21:49
• Updated: 02/Oct/19 17:15
• Resolved: 15/Feb/17 11:12

Description

If NameNode is unable to find plugins (specified in dfs.namenode.plugins), it terminates abruptly with the following stack trace:

Failed to start namenode.
java.lang.RuntimeException: java.lang.ClassNotFoundException: Class XXX not found
  at org.apache.hadoop.conf.Configuration.getClasses(Configuration.java:2178)
  at org.apache.hadoop.conf.Configuration.getInstances(Configuration.java:2250)
  at org.apache.hadoop.hdfs.server.namenode.NameNode.startCommonServices(NameNode.java:713)
  at org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:691)
  at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:843)
  at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:822)
  at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1543)
  at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1611)

We should catch this exception, log a warning message and let it proceed, as missing the third party library does not affect the functionality of NameNode. We caught this bug during a CDH upgrade where a third party plugin was not in the lib directory of the newer version of CDH.