Commit Graph

107 Commits

Author SHA1 Message Date
Joshua Boniface 611e0edd80 Reorder last keepalive during cleanup
Make sure the stopping of the keepalive timer and final keepalive update
are done as the last step before complete shutdown. The previous setup
could conceivably result in a node being fenced should the cleanup
operations take longer than ~45 seconds, for instance if primary node
switchover took too long or blocked, or log watchers failed to stop
quickly enough. Ensures that keepalives will continue to be run during
the shutdown process until the last possible moment.
2020-04-12 03:49:29 -04:00
Joshua Boniface b413e042a6 Improve handling of primary contention
Previously, contention could occasionally cause a flap/dual primary
contention state due to the lack of checking within this function. This
could cause a state where a node transitions to primary than is almost
immediately shifted away, which could cause undefined behaviour in the
cluster.

The solution includes several elements:
    * Implement an exclusive lock operation in zkhandler
    * Switch the become_primary function to use this exclusive lock
    * Implement exclusive locking during the contention process
    * As a failsafe, check stat versions before setting the node as the
      primary node, in case another node already has
    * Delay the start of takeover/relinquish operations by slightly
      longer than the lock timeout
    * Make the current router_state conditions more explicit (positive
      conditionals rather than negative conditionals)

The new scenario ensures that during contention, only one secondary will
ever succeed at acquiring the lock. Ideally, the other would then grab
the lock and pass, but in testing this does not seem to be the case -
the lock always times out, so the failsafe check is technically not
needed but has been left as an added safety mechanism. With this setup,
the node that fails the contention will never block the switchover nor
will it try to force itself onto the cluster after another node has
successfully won contention.

Timeouts may need to be adjusted in the future, but the base timeout of
0.4 seconds (and transition delay of 0.5 seconds) seems to work reliably
during preliminary tests.
2020-04-12 03:40:17 -04:00
Joshua Boniface a671d9d457 Use consistent tense in messages 2020-04-08 22:00:51 -04:00
Joshua Boniface fee1c7dd6c Reorder cleanup and gracefully wait for flushes 2020-04-08 22:00:08 -04:00
Joshua Boniface d2a5fe59c0 Use transitional takeover states for migration
Use a pair of transitional states, "takeover" and "relinquish", when
transitioning between primary and secondary coordinator states. This
provides a clsuter-wide record that the nodes are still working during
their synchronous transition states, and should allow clients to
determine when the node(s) have fully switched over. Also add an
additional 2 seconds of wait at the end of the transition jobs to ensure
everything has had a chance to start before proceeding.

References #72
2020-02-19 14:06:54 -05:00
Joshua Boniface 9c7041f12c Update package version to 0.7 2020-02-15 23:25:47 -05:00
Joshua Boniface ce985234c3 Use consistent naming of components
Rename "pvcd" to "pvcnoded", and "pvc-api" to "pvcapid" so names for the
daemons are fully consistent. Update the names of the configuration
files as well to match this new formatting.

References #79
2020-02-08 19:34:07 -05:00