Most of these would silently fail if there was e.g. an issue with the ZK
connection. Instead, encase things in try blocks and handle the
exceptions in a more graceful way, returning None or False if
applicable. Except for locks, which should retry 5 times before
aborting.
Using simple print statements was annoying (lack of timing info and
formatting), so move to using the debug logger for these instead with a
custom state ('d') with white text to differentiate them. Also indicate
which subthread of the keepalive each task is being executed in for
easier tracing of issues.
Verify our IPMI state on startup, and then warn if fencing will fail.
For now, this is sufficient, but in future (requires refactoring) we
might want to adjust how fencing occurs based on this information.
Using the Ceph library was a disaster here; it had no timeout or way to
force it to continue, so keepalives would become stuck and trigger fence
storms. Go back to the manual osd dump command with a 2s timeout which
is far more reliable and can be adequately terminated if it runs long.
Prevent the main keepalive thread from getting stuck due to a subthread
taking an enormous time. If this happens, the rest of the main keepalive
will continue onward, thus ensuring that the main keepalive does not
fail for a significant number of cycles, which would cause a fence.
The previous saving throw limit (3/15s) seems to have been too low. I
was observing bizarre failures where a node would be fenced while it was
still starting up. Some of this may have been related to Zookeeper
connections taking too long, but this was inconsistent.
Increase this to 6 saving throws (30s). This provides significantly more
time for a node to properly check in on startup before another node
fences it. In the real world, 15s vs 30s isn't that big of a downtime
change, but prevents false-positive fences.
Provides a CLI and API argument to force live migration, which triggers
a new VM state "migrate-live". The node daemon VMInstance during migrate
will read this flag from the state and, if enforced, will not trigger a
shutdown migration.
Closes#95
Prevents a rare edge case where a node can end up "migrating" to itself.
Quick hack to fix this, though like most of the VM management should
probably be rethought/rewritten later.
Fixes#92
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.
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.
This may or may not help, but should in theory prevent the flush from
trying to run after a (locally-running) API daemon is terminated, which
could cause an API failure and a failure to flush.
This will stop systemd from killing the service in the middle of a flush
or unflush operation, which completely defeats the purpose. 30 minutes
was chosen as this is a very large but still somewhat manageable value,
which should cover even a very large very loaded cluster with room to
spare.
Most of these actions/conditionals were looking for primary state, but
were failing during node takeover. Update the conditionals to look for
both router states instead.
Also add a wait to lock flushing until a takeover is completed.
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
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
Modifies the storage and upstream networks to mirror the cluster
network, with a bridge on top of the underlying specified dev, and all
IPs bound to the bridge.
Allows creating VMs in the storage or upstream networks, as well as the
cluster network, should the administrator choose to do so (manually).
Implements a "maintenance mode" for PVC clusters. For now, the only
thing this mode does is disable node fencing while the state is true.
This allows the administrator to tell PVC that network connectivity,
etc. might be interrupted and to avoid fencing nodes.
Closes#70
Required due to #64. Bridged networks were being created on top of a
vLAN if the Cluster network was a vLAN device, rather than being created
on the underlying device. This came from a previous revision of the
cluster architecture guidelines where Cluster was supposed to be a raw
device rather than a vLAN. This fixed the problem by implementing a
configuration field for a "bridge_device", a NIC device that can then
have the bridged vLANs created on top of it.
Fixes#64
Prevents blocking the main thread(s) while a VM is changing state. In
particular, this caused some issues with nodes not responding to
cancellation/reversal of a flush/ready state until the previous
migration was finished, which could cause issues. This entire subset of
actions is now threaded and so can run on its own in the background.
This particular arping interval/count, along with forcing it to run in
the foreground, seems to minimize the packet loss when the primary
coordinator transitions. Through extensive testing, this value results
in the, consistently, least amount of loss: 1-2 pings, at an 0.025s ping
interval, return "TTL exceeded", with no other loss, and only when the
node the test VM is on is the one switching to secondary state. No other
combination of values here, nor tweaks to other parts of the code, seem
able to reduce this further, therefore this is likely the best
configuration possible.
The previous method was a "throw it in the sea"-type migration with some
(very arbitrary) sleep statements thrown in for good measure.
Reimplement this with some hard locking. During each phase of the
transition, the nodes acquire read/write shared locks to a Zookeeper key
so that they can tightly coordinate the actions of transferring each
part of the primary state between them. This is done in a subthread to
prevent strange blocking issues that were encountered, likely due to
business in the existing main thread.
Joshua Boniface