Sending logs to a backend

The gateway keeps no log file: it writes to stderr, and these are the ways to take the logs from there.

Fluent Bit, through a pipe. If it exits, the gateway keeps serving, but the logs stop until both are restarted:

./warmphp app.php 2>&1 >/dev/null | fluent-bit -i stdin -o stdout

Docker, with its fluentd log driver. It sends the container's stream to Fluent Bit, wrapping each record in a log field. With fluentd-async=true, the container starts even when Fluent Bit is down:

docker run --log-driver fluentd --log-opt fluentd-address=127.0.0.1:24224 \
  --log-opt fluentd-async=true --log-opt tag=warmphp ...

Fluent Bit opens the log field with a parser that knows the gateway's time format. In a file, here warmphp.conf:

[PARSER]
    Name        warmphp
    Format      json
    Time_Key    time
    Time_Format %Y-%m-%dT%H:%M:%S.%L%z

fluent-bit -R warmphp.conf -i forward -p port=24224 \
  -F parser -m '*' -p key_name=log -p parser=warmphp -o stdout -m '*'

Replace -o stdout with the output of your backend.

A file, read by the OpenTelemetry Collector. Redirect stderr to it, and rotate it with logrotate and copytruncate, as nothing else does:

./warmphp app.php 2>> /logs/gateway.log

The OpenTelemetry Collector reads the records as logs. This configuration of its contrib distribution (tested on 0.164) sets the time, the severity, the body and the trace id. include is the path as the Collector sees it:

receivers:
  file_log:
    include: [/logs/gateway.log]
    operators:
      - type: json_parser
        timestamp:
          parse_from: attributes.time
          layout_type: gotime
          layout: 2006-01-02T15:04:05.999999999Z07:00
        severity:
          parse_from: attributes.level
      - type: move
        from: attributes.msg
        to: body
      - type: trace_parser
        if: attributes.trace_id != nil
        trace_id:
          parse_from: attributes.trace_id
exporters:
  debug:
service:
  pipelines:
    logs:
      receivers: [file_log]
      exporters: [debug]

Replace debug with the exporter of your backend.

See the log field reference for units and request correlation.