In Nomad 0.12.1 we introduced atomic job registration/deregistration, where the
new eval was written in the same raft entry. Backwards-compatibility checks were
supposed to have been removed in Nomad 1.1.0, but we missed that. This is long
safe to remove.
The signature of the `raftApply` function requires that the caller unwrap the
first returned value (the response from `FSM.Apply`) to see if it's an
error. This puts the burden on the caller to remember to check two different
places for errors, and we've done so inconsistently.
Update `raftApply` to do the unwrapping for us and return any `FSM.Apply` error
as the error value. Similar work was done in Consul in
https://github.com/hashicorp/consul/pull/9991. This eliminates some boilerplate
and surfaces a few minor bugs in the process:
* job deregistrations of already-GC'd jobs were still emitting evals
* reconcile job summaries does not return scheduler errors
* node updates did not report errors associated with inconsistent service
discovery or CSI plugin states
Note that although _most_ of the `FSM.Apply` functions return only errors (which
makes it tempting to remove the first return value entirely), there are few that
return `bool` for some reason and Variables relies on the response value for
proper CAS checking.
* One-time tokens are not replicated between regions, so we don't want to enforce
that the version check across all of serf, just members in the same region.
* Scheduler: Disconnected clients handling is specific to a single region, so we
don't want to enforce that the version check across all of serf, just members in
the same region.
* Variables: enforce version check in Apply RPC
* Cleans up a bunch of legacy checks.
This changeset is specific to 1.4.x and the changes for previous versions of
Nomad will be manually backported in a separate PR.
Fixes a bug where Nomad reports negative or incorrect running children
counts for periodic jobs.
The periodic dispatcher derives a child job without reseting the status.
If the periodic job has a `running` status, the derived job will start
as `running` status and transition to `pending`. Since this is
unexpected transition, the counting in StateStore.setJobSummary gets out of sync and
result in negative/incorrect values.
Note that this only affects periodic jobs after a leader transition.
During the first job registration, the job is added with `pending` or
`""` status. However, after a leader transition, the new leader
repopulates the dispatcher heap with `"running"` status and triggers the
bug.
This fixes a bug where jobs may get "stuck" unprocessed that
dispropotionately affect periodic jobs around leadership transitions.
When registering a job, the job registration and the eval to process it
get applied to raft as two separate transactions; if the job
registration succeeds but eval application fails, the job may remain
unprocessed. Operators may detect such failure, when submitting a job
update and get a 500 error code, and they could retry; periodic jobs
failures are more likely to go unnoticed, and no further periodic
invocations will be processed until an operator force evaluation.
This fixes the issue by ensuring that the job registration and eval
application get persisted and processed atomically in the same raft log
entry.
Also, applies the same change to ensure atomicity in job deregistration.
Backward Compatibility
We must maintain compatibility in two scenarios: mixed clusters where a
leader can handle atomic updates but followers cannot, and a recent
cluster processes old log entries from legacy or mixed cluster mode.
To handle this constraints: ensure that the leader continue to emit the
Evaluation log entry until all servers have upgraded; also, when
processing raft logs, the servers honor evaluations found in both spots,
the Eval in job (de-)registration and the eval update entries.
When an updated server sees mix-mode behavior where an eval is inserted
into the raft log twice, it ignores the second instance.
I made one compromise in consistency in the mixed-mode scenario: servers
may disagree on the eval.CreateIndex value: the leader and updated
servers will report the job registration index while old servers will
report the index of the eval update log entry. This discripency doesn't
seem to be material - it's the eval.JobModifyIndex that matters.
PeriodicDispatch.SetEnabled sets updateCh in one goroutine, and
PeriodicDispatch.run accesses updateCh in another.
The race can be prevented by having SetEnabled pass updateCh to run.
Race detector output from `go test -race -run TestServer_RPC` in nomad/
```
==================
WARNING: DATA RACE
Write at 0x00c0001d3f48 by goroutine 75:
github.com/hashicorp/nomad/nomad.(*PeriodicDispatch).SetEnabled()
/home/schmichael/go/src/github.com/hashicorp/nomad/nomad/periodic.go:468
+0x256
github.com/hashicorp/nomad/nomad.(*Server).revokeLeadership()
/home/schmichael/go/src/github.com/hashicorp/nomad/nomad/leader.go:724
+0x267
github.com/hashicorp/nomad/nomad.(*Server).leaderLoop.func1()
/home/schmichael/go/src/github.com/hashicorp/nomad/nomad/leader.go:131
+0x3c
github.com/hashicorp/nomad/nomad.(*Server).leaderLoop()
/home/schmichael/go/src/github.com/hashicorp/nomad/nomad/leader.go:163
+0x4dd
github.com/hashicorp/nomad/nomad.(*Server).monitorLeadership.func1()
/home/schmichael/go/src/github.com/hashicorp/nomad/nomad/leader.go:72
+0x6c
Previous read at 0x00c0001d3f48 by goroutine 515:
github.com/hashicorp/nomad/nomad.(*PeriodicDispatch).run()
/home/schmichael/go/src/github.com/hashicorp/nomad/nomad/periodic.go:338
+0x177
Goroutine 75 (running) created at:
github.com/hashicorp/nomad/nomad.(*Server).monitorLeadership()
/home/schmichael/go/src/github.com/hashicorp/nomad/nomad/leader.go:70
+0x269
Goroutine 515 (running) created at:
github.com/hashicorp/nomad/nomad.(*PeriodicDispatch).SetEnabled()
/home/schmichael/go/src/github.com/hashicorp/nomad/nomad/periodic.go:176
+0x1bc
github.com/hashicorp/nomad/nomad.(*Server).establishLeadership()
/home/schmichael/go/src/github.com/hashicorp/nomad/nomad/leader.go:231
+0x582
github.com/hashicorp/nomad/nomad.(*Server).leaderLoop()
/home/schmichael/go/src/github.com/hashicorp/nomad/nomad/leader.go:117
+0x82e
github.com/hashicorp/nomad/nomad.(*Server).monitorLeadership.func1()
/home/schmichael/go/src/github.com/hashicorp/nomad/nomad/leader.go:72
+0x6c
==================
```
