When claiming a CSI volume, we need to ensure the CSI node plugin is running
before we send any CSI RPCs. This extends even to the controller publish RPC
because it requires the storage provider's "external node ID" for the
client. This primarily impacts client restarts but also is a problem if the node
plugin exits (and fingerprints) while the allocation that needs a CSI volume
claim is being placed.
Unfortunately there's no mapping of volume to plugin ID available in the
jobspec, so we don't have enough information to wait on plugins until we either
get the volume from the server or retrieve the plugin ID from data we've
persisted on the client.
If we always require getting the volume from the server before making the claim,
a client restart for disconnected clients will cause all the allocations that
need CSI volumes to fail. Even while connected, checking in with the server to
verify the volume's plugin before trying to make a claim RPC is inherently racy,
so we'll leave that case as-is and it will fail the claim if the node plugin
needed to support a newly-placed allocation is flapping such that the node
fingerprint is changing.
This changeset persists a minimum subset of data about the volume and its plugin
in the client state DB, and retrieves that data during the CSI hook's prerun to
avoid re-claiming and remounting the volume unnecessarily.
This changeset also updates the RPC handler to use the external node ID from the
claim whenever it is available.
Fixes: #13028
new WaitForPlugin() called during csiHook.Prerun,
so that on startup, clients can recover running
tasks that use CSI volumes, instead of them being
terminated and rescheduled because they need a
node plugin that is "not found" *yet*, only because
the plugin task has not yet been recovered.
The allocrunner has a facility for passing data written by allocrunner hooks to
taskrunner hooks. Currently the only consumers of this facility are the
allocrunner CSI hook (which writes data) and the taskrunner volume hook (which
reads that same data).
The allocrunner hook for CSI volumes doesn't set the alloc hook resources
atomically. Instead, it gets the current resources and then writes a new version
back. Because the CSI hook is currently the only writer and all readers happen
long afterwards, this should be safe but #16623 shows there's some sequence of
events during restore where this breaks down.
Refactor hook resources so that hook data is accessed via setters and getters
that hold the mutex.
When we unmount a volume we need to be able to recover from cases
where the plugin has been shutdown before the allocation that needs
it, so in #11892 we blocked shutting down the alloc runner hook. But
this blocks client shutdown if we're in the middle of unmounting. The
client won't be able to communicate with the plugin or send the
unpublish RPC anyways, so we should cancel the context and assume that
we'll resume the unmounting process when the client restarts.
For `-dev` mode we don't send the graceful `Shutdown()` method and
instead destroy all the allocations. In this case, we'll never be able
to communicate with the plugin but also never close the context we
need to prevent the hook from blocking. To fix this, move the retries
into their own goroutine that doesn't block the main `Postrun`.
When the alloc runner claims a volume, an allocation for a previous
version of the job may still have the volume claimed because it's
still shutting down. In this case we'll receive an error from the
server. Retry this error until we succeed or until a very long timeout
expires, to give operators a chance to recover broken plugins.
Make the alloc runner hook tolerant of temporary RPC failures.
When an allocation stops, the `csi_hook` makes an unpublish RPC to the
servers to unpublish via the CSI RPCs: first to the node plugins and
then the controller plugins. The controller RPCs must happen after the
node RPCs so that the node has had a chance to unmount the volume
before the controller tries to detach the associated device.
But the client has local access to the node plugins and can
independently determine if it's safe to send unpublish RPC to those
plugins. This will allow the server to treat the node plugin as
abandoned if a client is disconnected and `stop_on_client_disconnect`
is set. This will let the server try to send unpublish RPCs to the
controller plugins, under the assumption that the client will be
trying to unmount the volume on its end first.
Note that the CSI `NodeUnpublishVolume`/`NodeUnstageVolume` RPCs can
return ignorable errors in the case where the volume has already been
unmounted from the node. Handle all other errors by retrying until we
get success so as to give operators the opportunity to reschedule a
failed node plugin (ex. in the case where they accidentally drained a
node without `-ignore-system`). Fan-out the work for each volume into
its own goroutine so that we can release a subset of volumes if only
one is stuck.
hc-github-team-nomad-core