The plan applier has to get a snapshot with a minimum index for the
plan it's working on in order to ensure consistency. Under heavy raft
loads, we can exceed the timeout. When this happens, we hit a bug
where the plan applier blocks waiting on the `indexCh` forever, and
all schedulers will block in `Plan.Submit`.
Closing the `indexCh` when the `asyncPlanWait` is done with it will
prevent the deadlock without impacting correctness of the previous
snapshot index.
This changeset includes the a PoC failing test that works by injecting
a large timeout into the state store. We need to turn this into a test
we can run normally without breaking the state store before we can
merge this PR.
Increase `snapshotMinIndex` timeout to 10s.
This timeout creates backpressure where any concurrent `Plan.Submit`
RPCs will block waiting for results. This sheds load across all
servers and gives raft some CPU to catch up, because schedulers won't
dequeue more work while waiting. Increase it to 10s based on
observations of large production clusters.
The Plan.Submit endpoint assumed PlanRequest.Plan was never nil. While
there is no evidence it ever has been nil, we should not panic if a nil
plan is ever submitted because that would crash the leader.
Copy the updated version of freeport (sdk/freeport), and tweak it for use
in Nomad tests. This means staying below port 10000 to avoid conflicts with
the lib/freeport that is still transitively used by the old version of
consul that we vendor. Also provide implementations to find ephemeral ports
of macOS and Windows environments.
Ports acquired through freeport are supposed to be returned to freeport,
which this change now also introduces. Many tests are modified to include
calls to a cleanup function for Server objects.
This should help quite a bit with some flakey tests, but not all of them.
Our port problems will not go away completely until we upgrade our vendor
version of consul. With Go modules, we'll probably do a 'replace' to swap
out other copies of freeport with the one now in 'nomad/helper/freeport'.
Tim Gross