The Deployment runs two replicas, but WebSocket subscribers live only in
each process's in-memory hub. Every replica races to read the same
global unpublished outbox rows, and publishing succeeded even when the
winning replica held no matching local subscriber -- that replica then
set the single global published_at. A client connected to the other
replica never received the event, and delivery degraded further with
each replica added. REST recovery eventually converged, but short-lived
proposal transitions could be observed late or not at all.
Publish committed events through PostgreSQL LISTEN/NOTIFY so the replica
that owns the subscriber's connection delivers it, regardless of which
replica drained the row. The listener holds its own pgx connection --
LISTEN is session state, so a pooled database/sql connection cannot
carry it -- and reconnects with backoff, since losing it would silently
downgrade that replica's subscribers to REST-only recovery.
The fan-out is optional: without EventFanout configured, behaviour is
unchanged local-hub publication, which stays correct for a single
replica and for tests. Only outbox-sourced events are routed through it;
the in-request-path publishes remain local, as those are a latency
optimisation for the caller's own connection.
Fan-out needs a wire shape of its own because ControlPlaneEvent hides
PlayerID from clients, and the recipient is exactly what a peer replica
needs to route on.
ApplyInitialConnectPlan wrote a payload of {match_id,state,action},
omitting event, revision, resource_id, occurred_at and player_ids --
every field deliverStateOutboxEvent requires. Delivery rejected the row,
dispatch returned on the first error so it was never acknowledged, and
because reads are ordered oldest-first it was retried ahead of every
later state_changed event on every 100ms poll. One initial-connect
transition therefore blocked lifecycle delivery for all matches, not
just its own.
Two independent fixes, since either alone leaves the system fragile:
Build envelopes through one validating helper (MarshalOutboxEnvelope)
and convert all five writers to it. A writer that omits a required
field now fails its own transaction instead of committing a row that
can only ever poison the queue. The helper takes revision as int64 so
the -1 "nothing matched" sentinel some CTEs return surfaces as an error
rather than wrapping to a huge uint64.
Make dispatch resilient regardless: a delivery failure is now counted
against that row and the batch continues, with the row dead-lettered
after MaxOutboxDeliveryAttempts so a poison event degrades to one lost
notification instead of a stalled queue. Ordering within an aggregate
is still honoured -- later events of a failed match are deferred, so no
client observes that match's newer state before its older state. An ack
failure still stops the batch, being a database rather than a payload
problem.
Initial-connect events now address every participant, not just the
connected ones: a no-show needs to learn their ticket was failed and a
penalty applied.
Josh Creek