Pipeline Doctor
Quick reference for PostHog's ingestion pipeline framework and its convention-checking agents.
Architecture overview
The ingestion pipeline processes events through a typed, composable step chain:
Kafka message
→ messageAware()
→ parse headers/body
→ sequentially() for preprocessing
→ filterMap() to enrich context (e.g., team lookup)
→ teamAware()
→ groupBy(token:distinctId)
→ concurrently() for per-entity processing
→ gather()
→ pipeBatch() for batch operations
→ handleIngestionWarnings()
→ handleResults()
→ handleSideEffects()
→ build()See nodejs/src/ingestion/analytics/joined-ingestion-pipeline.ts for the real implementation.
Key file locations
| What | Where |
|---|---|
| Step type | nodejs/src/ingestion/pipelines/steps.ts |
| Result types | nodejs/src/ingestion/pipelines/results.ts |
| Doc-test chapters | nodejs/src/ingestion/pipelines/docs/*.test.ts |
| Joined pipeline | nodejs/src/ingestion/analytics/joined-ingestion-pipeline.ts |
| Doctor agents | .claude/agents/ingestion/ |
| Test helpers | nodejs/src/ingestion/pipelines/docs/helpers.ts |
Which agent to use
| Concern | Agent | When to use |
|---|---|---|
| Step structure | pipeline-step-doctor | Factory pattern, type extension, config injection, naming |
| Result handling | pipeline-result-doctor | ok/dlq/drop/redirect, side effects, ingestion warnings |
| Composition | pipeline-composition-doctor | Builder chain, concurrency, grouping, branching, retries |
| Testing | pipeline-testing-doctor | Test helpers, assertions, fake timers, doc-test style |
Quick convention reference
Steps: Factory function returning a named inner function. Generic <T extends Input> for type extension. No any. Config via closure.
Results: Use ok(), dlq(), drop(), redirect() constructors. Side effects as promises in ok(value, [effects]). Warnings as third parameter.
Composition: messageAware wraps the pipeline. handleResults inside messageAware. handleSideEffects after. groupBy + concurrently for per-entity work. gather before batch steps.
Testing: Step tests call factory directly. Use consumeAll()/collectBatches() helpers. Fake timers for async. Type guards for result assertions. No any.
Running all doctors
Ask Claude to "run all pipeline doctors on my recent changes" to get a comprehensive review across all 4 concern areas.