/*
* TODO:
* we need to make sure that if we get fenced and then quickly restarted,
* none of these calls will retry across the restart boundary
* perhaps the solution is that, whenever the nn starts, it gets a unique
* ID, and when we start becoming active, we record it, and then any future
* calls use the same ID
*/
/// <summary>Store the results of the last attempt to become active.</summary>
/// <remarks>
/// Store the results of the last attempt to become active.
/// This is used so that, during manually initiated failover,
/// we can report back the results of the attempt to become active
/// to the initiator of the failover.
/// </remarks>
private void RecordActiveAttempt(ZKFailoverController.ActiveAttemptRecord record)
{
lock (activeAttemptRecordLock)
{
lastActiveAttemptRecord = record;
Runtime.NotifyAll(activeAttemptRecordLock);
}
}
/// <summary>Coordinate a graceful failover.</summary>
/// <remarks>
/// Coordinate a graceful failover. This proceeds in several phases:
/// 1) Pre-flight checks: ensure that the local node is healthy, and
/// thus a candidate for failover.
/// 2) Determine the current active node. If it is the local node, no
/// need to failover - return success.
/// 3) Ask that node to yield from the election for a number of seconds.
/// 4) Allow the normal election path to run in other threads. Wait until
/// we either become unhealthy or we see an election attempt recorded by
/// the normal code path.
/// 5) Allow the old active to rejoin the election, so a future
/// failback is possible.
/// </remarks>
/// <exception cref="Org.Apache.Hadoop.HA.ServiceFailedException"/>
/// <exception cref="System.IO.IOException"/>
/// <exception cref="System.Exception"/>
private void DoGracefulFailover()
{
int timeout = FailoverController.GetGracefulFenceTimeout(conf) * 2;
// Phase 1: pre-flight checks
CheckEligibleForFailover();
// Phase 2: determine old/current active node. Check that we're not
// ourselves active, etc.
HAServiceTarget oldActive = GetCurrentActive();
if (oldActive == null)
{
// No node is currently active. So, if we aren't already
// active ourselves by means of a normal election, then there's
// probably something preventing us from becoming active.
throw new ServiceFailedException("No other node is currently active.");
}
if (oldActive.GetAddress().Equals(localTarget.GetAddress()))
{
Log.Info("Local node " + localTarget + " is already active. " + "No need to failover. Returning success."
);
return;
}
// Phase 3: ask the old active to yield from the election.
Log.Info("Asking " + oldActive + " to cede its active state for " + timeout + "ms"
);
ZKFCProtocol oldZkfc = oldActive.GetZKFCProxy(conf, timeout);
oldZkfc.CedeActive(timeout);
// Phase 4: wait for the normal election to make the local node
// active.
ZKFailoverController.ActiveAttemptRecord attempt = WaitForActiveAttempt(timeout +
60000);
if (attempt == null)
{
// We didn't even make an attempt to become active.
lock (this)
{
if (lastHealthState != HealthMonitor.State.ServiceHealthy)
{
throw new ServiceFailedException("Unable to become active. " + "Service became unhealthy while trying to failover."
);
}
}
throw new ServiceFailedException("Unable to become active. " + "Local node did not get an opportunity to do so from ZooKeeper, "
+ "or the local node took too long to transition to active.");
}
// Phase 5. At this point, we made some attempt to become active. So we
// can tell the old active to rejoin if it wants. This allows a quick
// fail-back if we immediately crash.
oldZkfc.CedeActive(-1);
if (attempt.succeeded)
{
Log.Info("Successfully became active. " + attempt.status);
}
else
{
// Propagate failure
string msg = "Failed to become active. " + attempt.status;
throw new ServiceFailedException(msg);
}
}
