[logging]

The Rust server's log format: human-readable text, or one JSON object per line for log shippers.

[logging]
format = "json"

Reference

Behavior

• GIO_LOG_FORMAT (json or text, any case) wins over the file, so one build can log text locally and JSON in its container. An invalid value is ignored with a warning: ignoring GIO_LOG_FORMAT="logfmt": expected "json" or "text".
• The Node worker always writes JSON lines with the same core keys and the request id as requestId; this key only switches the server's own lines.
• Levels are filtered with RUST_LOG for the server (default info) and GIO_LOG_LEVEL for the worker.

{"ts":"2026-10-06T12:00:01.204518Z","level":"info","msg":"request completed","target":"giojs_server","cache":"miss","method":"GET","path":"/posts/7","request_id":"0b8e3c52-7a1d-4f0e-9c3b-5d2a6e8f1a47","status":"200"}

Examples

JSON in production, text locally

Leave gio.toml at the default and set the variable where the logs are shipped:

ENV GIO_LOG_FORMAT=json

Good to know

• format = "logfmt" stops startup: invalid `logging.format`: unknown variant `logfmt`, expected `text` or `json`.
• Event or span fields named ts, level, msg or target are written as field.<name> instead of overwriting the core keys.

Related

• Observability: JSON logs
• Request IDs
• Environment variables

Version history