fix: MutexOwner retries on transient Redis errors instead of crashing#2131
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isaacrowntree wants to merge 3 commits into
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fix: MutexOwner retries on transient Redis errors instead of crashing#2131isaacrowntree wants to merge 3 commits into
isaacrowntree wants to merge 3 commits into
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When Redis (or a Redis-compatible store like Dragonfly/KeyDB) restarts,
MutexOwner would immediately crash with {:shutdown, :err_keeping_mutex}.
Since MutexedSupervisor uses :one_for_all strategy, this cascades and
takes down the entire Runtime.Supervisor including all consumers.
The fix:
- MutexOwner now retries up to 5 times with backoff on Redis errors
while in :has_mutex state, giving Redis time to come back
- Resets the error counter on successful reconnection
- Also fixes the GenStateMachine return value (was {:shutdown, reason}
which is invalid - now {:stop, {:shutdown, reason}})
- LiveView pages (index.ex, show.ex) now handle Redis errors gracefully
in metrics loading instead of crashing with MatchError
Fixes sequinstream#2072
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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…s errors Instead of giving up after N errors, MutexOwner now retries indefinitely with exponential backoff capped at 1 hour. Redis going down should never crash Sequin — it should degrade gracefully and self-heal when Redis returns. Integration tests use iptables REJECT to simulate a real Redis/Dragonfly redeploy and verify the process survives the outage and recovers. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
…ation tests Unit tests (6, <0.1s): verify backoff math, error counter behavior, and state struct defaults without needing Redis. Integration tests (2, ~35s each, tagged :integration): use iptables REJECT to simulate Redis going down, verifying the process survives and recovers. Run with: mix test --include integration Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Since upstream appears unmaintained (no maintainer activity since Feb 2026), this fix is now merged and released in the maintained fork at https://github.com/triptechtravel/sequin — release v0.14.6-tt2, image |
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Summary
Fixes #2072 — When Redis (or a Redis-compatible store like Dragonfly/KeyDB) restarts, Sequin enters an unrecoverable failure state requiring a full restart. This has bitten us (and others per #2072) multiple times in production.
Root cause:
MutexOwnerin:has_mutexstate callsacquire_mutexwhich returns:errorwhen Redis is unreachable. The handler immediately returns{:shutdown, :err_keeping_mutex}— an invalid GenStateMachine return that crashes the process with{:bad_return_from_state_function, ...}. Due toMutexedSupervisor's:one_for_allstrategy, this cascades and takes down the entireRuntime.Supervisorincluding all consumers.Changes:
MutexOwner: Instead of crashing on Redis errors, retry indefinitely with exponential backoff (capped at 1 hour). When Redis comes back, the error counter resets and normal operation resumes. Also fixes the GenStateMachine return value ({:stop, {:shutdown, reason}}instead of invalid{:shutdown, reason}).SinkConsumersLive.Index: Handle{:error, _}from metrics calls instead of crashing withMatchError.SinkConsumersLive.Show: Same defensive handling for all three metrics calls.HttpEndpointsLive.Show: Same fix forget_http_endpoint_throughput/1.Context
We self-host Sequin on Railway with Dragonfly (Redis-compatible) as the backing store. Railway periodically auto-updates Dragonfly, which causes a brief restart. Every time this happens, Sequin fails to self-heal and requires a manual restart — we've hit this 3 times now. The
:await_mutexstate already retries correctly on Redis errors; this PR brings the same resilience to the:has_mutexstate, but with exponential backoff so it doesn't spam during extended outages.Test plan
MutexOwnerTestwith unit tests for State struct and integration tests (tagged:integration) that useiptables REJECTto simulate Redis going down and coming backmix test)mix format --check-formattedpassesNote: Integration tests require
NET_ADMINcapability (for iptables) and are tagged:integrationso they can be excluded from normal test runs:mix test --exclude integration🤖 Generated with Claude Code