Inspect the local BullMQ surface before changing code:
- Package versions for bullmq, optional peers (ioredis, redis, pg, bullmq-otel), @nestjs/bullmq if present, Node/Bun, and TypeScript.
- Backend: default Redis (connection options or a client) vs createPostgresBackend / setDefaultBackendFactory.
- Connection shape: options object vs shared client vs adapters (createNodeRedisClient, createBunRedisClient, createValkeyGlideClient); Redis prefix vs Postgres schema.
- Producers (Queue, FlowProducer) vs consumers (Worker); process isolation (inline vs sandboxed file / worker threads).
- Default job options, schedulers, rate limits, dedupe usage, Nest module registration if present.
Refresh current official docs when the task depends on latest APIs, version drift, Pro features, adapters, Postgres, or Nest wrappers. Start from source-map.md.
Route the work to the focused references:
- Setup, Redis/Postgres backends, Queue, Worker, QueueEvents: setup-connections.md.
- Job lifecycle and JobsOptions: jobs-options.md.
- Parent-child flows / FlowProducer: flows.md.
- Retries, delays, job schedulers, rate limits, dedupe: retries-scheduling-limits.md.
- Ops, v5→v6 upgrade, testing, NestJS, Pro vs OSS, polyglot: production-ops-integrations.md.
Preserve the repository's existing connection factories, Nest modules, and deployment topology unless the user explicitly asks for a migration.
Verify behavior at the narrowest useful boundary (processor unit), then queue/worker integration.

Core Judgment

Treat the datastore as shared infrastructure. Reuse connection options or factories deliberately. Workers and QueueEvents still duplicate connections for blocking wait; Redis clients/adapters must support duplicate().
Default Redis path requires the optional ioredis peer. Do not assume bullmq still bundles ioredis. ioredis 6.0 (RESP3 by default, Node 20+) satisfies the >=5.0.0 peer range, but BullMQ still tests against ioredis 5.11 and an open issue reports ioredis 6 RedisOptions not assignable to ConnectionOptions. Prefer bun add bullmq ioredis@5 unless the project already runs ioredis 6 and its typecheck + integration tests pass.
Non-Redis backends (Postgres or custom): pass the factory last and let TypeScript infer backend + connection types, or bind once with withBackend(createPostgresBackend) (6.3.9+) when you also need job type arguments. Never write partial generics like Queue<Data, Result, string, PostgresQueueBackend> — the 4th Queue slot is not the backend.
High-level classes are datastore-agnostic. Do not use removed Queue#client, Queue#redisVersion, Queue#databaseType, Worker#blockingClient, or FlowProducer#client. Reach Redis via queue.getBackend().client (typed as RedisQueueBackend) only as an escape hatch.
waitUntilReady() resolves to void. Do not treat its return as a Redis client. await worker.resume().
Attach error listeners on Queue, Worker, QueueEvents, and FlowProducer. Unhandled connection errors crash Node.
Design processors as idempotent. Jobs can retry, stall after lock loss, or run more than once.
Set attempts and backoff intentionally. Throw UnrecoverableError for poison/permanent failures (Job#discard() is removed). Throw Error objects, not strings.
Prefer FlowProducer for parent-child graphs. Flow parents must not set deduplication. Flow job opts omit repeat. Nodes without opts.jobId get UUIDs. Pick child failure opts deliberately (failParentOnFailure, ignoreDependencyOnFailure, removeDependencyOnFailure, continueParentOnFailure).
Recurring work is Job Schedulers only: upsertJobScheduler / getJobSchedulers / removeJobScheduler. Do not resurrect Queue.add(..., { repeat }), Repeat, getRepeatableJobs, removeRepeatable, removeRepeatableByKey, debounce, Job#debounceId, the debounced event, QueueScheduler, or pre-v3 groupKey rate limits on BullMQ 6.x. Group rate limits are Pro-only.
Deduplication needs a stable deduplication.id. Choose simple vs throttle (ttl) vs debounce (extend/replace + delay) vs keepLastIfActive.
Rate limiting is global per queue across workers. Prefer queue.rateLimit (Worker #rateLimit is deprecated). Optional queue-level setGlobalConcurrency / setGlobalRateLimit cap all workers; per-worker concurrency/limiter cannot exceed them.
Priority: lower number wins among prioritized jobs (1..2097151); unset/0 is unprioritized and is processed before any prioritized job. Paused queues still hold jobs as waiting — paused is not a job state in getJobCounts() / JobType.
Tune removeOnComplete / removeOnFail (age or count keep policies). Unbounded completed/failed sets grow without bound. Never use ioredis keyPrefix; use BullMQ prefix (brace hash tags on Cluster). Postgres uses schema, not Redis prefix.
Close workers gracefully on shutdown (await worker.close()). Killing processes mid-lock causes stalls and duplicate work unless ops expect that window.
Prefer @nestjs/bullmq over legacy @nestjs/bull. Do not recommend BullMQ Pro-only APIs (groups, group rate limits, worker job.getBatch(), observables) unless the project already uses Pro.
Keep processors thin and non-blocking on the event loop. Use sandboxed processors / useWorkerThreads when CPU-heavy or crash-isolating work is required. Job data is plaintext — avoid secrets or encrypt fields.
Redis remains the default, battle-tested backend. Use PostgreSQL (createPostgresBackend, explicit runMigrations) only when the project chooses a single-database model. Do not mix Redis and Postgres for the same queue.

Verification

Prefer repository-owned commands. For meaningful BullMQ changes, cover the relevant subset:

Typecheck Queue/Worker/FlowProducer options (including backend generic), job data/returnvalue/ProgressType types, and Nest injection tokens if used.
Unit-test processor success, retryable failure, UnrecoverableError, progress, and AbortSignal cancellation in isolation.
Integration test against Redis or Postgres: add → process → complete/fail; assert job state transitions. await worker.waitUntilReady() before adding jobs (returns void).
Delayed/scheduler tests with short intervals; assert no duplicate schedules after redeploy (upsertJobScheduler). Confirm no leftover repeat / getRepeatableJobs usage.
Rate-limit / dedupe tests: assert ignored/replaced/deferred behavior and deduplicated events (not debounced).
Flow tests: children complete before parent; parent reads getChildrenValues; child failure policy matches product intent; parent nodes reject deduplication.
Stall/lock smoke when changing lockDuration, stalledInterval, maxStalledCount, or long-running processors.
Graceful-shutdown smoke: SIGTERM/close path finishes in-flight work without unexpected orphaned locks beyond the stall window.
NestJS module smoke: queue registration, WorkerHost processors, and FlowProducer injection when Nest is in play.
Postgres: runMigrations applied; SchemaVersionMismatchError / SchemaMigrationRequiredError not hit at boot.
Redis growth check when changing retention (removeOnComplete/removeOnFail) or adding high-throughput queues.

Report which checks ran, which did not, and any Pro/OSS, Redis-vs-Postgres, or package-version assumptions that remain.

bullmq

BullMQ

Workflow