Containers: Stream container stdout/stderr to Workers Observability logs

[alexminza]

Describe the solution

Summary

Container stdout/stderr from processes started via sandbox.startProcess() should be continuously forwarded to Workers Observability (dashboard logs, wrangler tail), similar to how console.log() in Workers is captured automatically.

Current behavior

• console.log() in the Worker → visible in Workers Observability ✅
• Container stdout/stderr → not captured ❌
• observability.logs.enabled: true in container config captures Sandbox runtime logs, but not stdout/stderr from user processes
• process.getLogs() returns a point-in-time snapshot — no streaming, no event subscription, no incremental reads

Workarounds

1. GET /debug/logs endpoint — Worker route that calls process.getLogs() on demand and returns stdout/stderr as JSON. Requires manual polling.
2. SSH (wrangler containers ssh <instance-id>) — interactive access, not suitable for monitoring.
3. Cron-based polling — scheduled Worker calls getLogs() periodically and forwards via console.log(). But getLogs() returns the full buffer each time with no offset/cursor, making incremental forwarding difficult.

None of these provide real-time, continuous log visibility comparable to what docker logs -f or platform-managed containers offer.

Proposed solution

Any of these would address the gap:

1. Automatic forwarding — container stdout/stderr from startProcess() processes automatically appears in Workers Observability when observability.logs.enabled: true
2. Event-based API — process.onLog(callback) or process.streamLogs() returning a ReadableStream that the Worker can consume and forward via console.log()
3. Incremental reads — process.getLogs({ since: timestamp }) or process.getLogs({ offset: byteOffset }) to enable efficient polling without re-reading the full buffer

Option 1 would be the most ergonomic — zero Worker code needed.

Use case

Running any app inside a Cloudflare Container via the Sandbox SDK. The app produces structured logs on stdout that are essential for debugging issues, failures, and configuration problems. Currently these logs are invisible unless you SSH into the container or build a custom polling endpoint.

Environment

• wrangler 4.76.0
• @cloudflare/sandbox (latest)
• Container started via sandbox.startProcess() with a custom entrypoint