Log ring buffer

The internal/logbuf/ package provides an io.Writer-shaped ring buffer used to capture process output and stream it to UI subscribers without blocking the producer.

Why a ring buffer

docker compose pull/up and the SimpleDeploy server itself produce bursty output. The dashboard wants both history (so a late-joining tab sees what happened) and a live feed. A bounded ring buffer gives both with constant memory.

Shape

A Buffer holds up to N entries (default 500, configurable via log_buffer_size). Each entry is {timestamp, line}. Write appends; the oldest entry is dropped when full. Subscribers receive new entries via a Go channel.

The buffer satisfies io.Writer, so it can be passed wherever the standard library wants a writer (e.g., cmd.Stdout, cmd.Stderr in the deployer).

Process log capture

At server startup, os.Pipe is wired between the process’s stdout/stderr file descriptors and a Buffer. A goroutine reads the pipe and forwards lines into the buffer. This captures everything the binary prints, including third-party library output, and makes it queryable through the API and viewable in the dashboard’s “System logs” page.

Per-app deploy logs

The deployer creates a per-deploy Buffer, passes it to the docker compose subprocess, and registers it under the app slug. The API serves recent contents on connect, then streams new entries.

WebSocket fan-out

/api/apps/{slug}/deploy-logs and /api/apps/{slug}/logs upgrade to WebSocket and subscribe to the relevant buffer. Slow consumers do not block the producer; if a subscriber’s channel fills, the buffer drops messages for that subscriber and emits a warning.

Lifecycle

Per-deploy buffers are kept until the app is removed or the buffer is GC’d after subscribers disconnect. The system buffer is process-lifetime.