[AMQ-5568] Deleting lock file on broker shut down can take a master broker down

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 5.11.0
• Fix Version/s: 5.12.0
• Component/s: Broker, Message Store
• Labels: persistence
• Assignee: Gary Tully
• Reporter: Torsten Mielke
• Created: 06/Feb/15 12:58
• Updated: 22/Sep/15 11:56
• Resolved: 05/Mar/15 13:29

Description

This problem may only occur on a shared file system master/slave setup.
I can reproduce reliably on a NFSv4 mount using a persistence adapter configuration like

<levelDB directory="/nfs/activemq/data/leveldb" lockKeepAlivePeriod="5000">
  <locker>
    <shared-file-locker lockAcquireSleepInterval="10000"/>
  </locker>
</levelDB>

However the problem is also reproducible using kahaDB.
Two broker instances competing for the lock on the shared storage (e.g. leveldb or kahadb). Lets say brokerA becomes master, broker B slave.

If brokerA looses access to the NFS share, it will shut down. As part of shutting down, it tries delete the lock file of the persistence adapter. Now since the NFS share is gone, all file i/o calls hang for a good while before returning errors. As such the broker shut down gets delayed.

In the meantime the slave broker B (not affected by the NFS problem) grabs the lock and becomes master.

If the NFS mount is restored while broker A (the previous master) still hangs on the file i/o operations (as part of its shutdown routine), the attempt to delete the persistence adapter lock file will finally succeed and broker A shuts down.

Deleting the lock file however also affects the new master broker B who periodically runs a keepAlive() check on the lock. That check verifies the file still exists and the FileLock is still valid. As the lock file got deleted, keepAlive() fails on broker B and that broker shuts down as well.
The overall result is that both broker instances have shut down despite an initially successful failover.

Using restartAllowed=true is not an option either as this can cause other problems in an NFS based master/slave setup.

Issue Links

• relates to: AMQ-5549 Shared Filesystem Master/Slave using NFSv4 allows both brokers become active at the same time
• relates to: AMQ-4705 Add keep alive support to shared file locker