Fixes the panic mentioned in
https://github.com/hashicorp/nomad/issues/3420#issuecomment-341666932
While a leader task dying serially stops all follower tasks, the
synchronizing of state is asynchrnous. Nomad can shutdown before all
follower tasks have updated their state to dead thus saving the state
necessary to hit this panic: *have a non-terminal alloc with a dead
leader.*
The actual fix is a simple nil check to not assume non-terminal allocs
leader's have a TaskRunner.
The Client.allocs map now contains all AllocRunners again, not just
un-GC'd AllocRunners. Client.allocs is only pruned when the server GCs
allocs.
Also stops logging "marked for GC" twice.
interface has 3 implementations:
1. local for blocking and moving data locally
2. remote for blocking and moving data from another node
3. noop for allocs that don't need to block
This PR does the following:
* Adds a mechanism to emit events in the TaskRunner
* Vendors a new version of Consul-Template that allows extraction of
missing dependencies
* Adds logic to our consul_template.go to determine missing events and
emit them in a batched fashion.
* Refactors the consul_template code to split the run method and take in
a config struct rather than many parameters.
Fixes https://github.com/hashicorp/nomad/issues/2578
When replacing an alloc the new alloc is blocked until the old alloc is
destroyed. This could cause a deadlock:
1. Destroying the old alloc includes a final sync of its status
2. Syncing status causes a GC
3. A GC looks for terminal allocs to cleanup
4. The GC waits for an alloc to stop completely before GC'ing
If the GC chooses the currently-being-destroyed-alloc to GC, the GC
deadlocks. If `client.max_parallel` deadlocks happen the GC is wedged
until the Nomad process is restarted.
Performing the final sync asynchronously is an ugly hack but prevents
the deadlock by allowing the final sync to occur after the alloc runner
has shutdown and been destroyed.
Since the AllocRunner.alloc struct can be mutated, most of AllocRunner
needs to acquire a lock to get the alloc's ID. Log lines always need to
include the alloc ID, so we often skipped acquiring a lock just to grab
the ID and accepted the race.
Let's make the race detector a little happier by storing the ID in a
single assignment field.
Task dir metadata is created in AllocRunner.Run which may not run before
an alloc is sync'd and Nomad exits. There's no reason not to just create
task dir metadata on restore if it doesn't exist.
This PR adds watching of allocation health at the client. The client can
watch for health based on the tasks running on time and also based on
the consul checks passing.
