egg-logger-fc

Ship Egg.js logs to Alibaba Cloud SLS via Function Compute stdout — JSON lines with the FC RequestId attached.

Why

FC 3.0 automatically collects everything an instance writes to stdout / stderr into the bound SLS Logstore (official doc). egg-logger's default behavior writes to local files under /tmp/log, which vanish when the FC instance is destroyed — SLS never sees them.

This plugin:

1. Disables egg-logger's file / jsonFile transports on every logger.
2. Replaces the console transport with a JSON one that writes to stdout (info / warn / debug) and stderr (error).
3. Attaches the FC x-fc-request-id header plus standard ctx fields (method, url, ip, userId, useMs) to every request-scoped log line, so each field becomes individually queryable in SLS.
4. Tags every line with the source logger's name (logger: "coreLogger" | "errorLogger" | "logger" | "<customLoggerName>"), so SLS queries can still split what used to live in egg-web.log / common-error.log / <app>-web.log / custom log files.

Install

npm i egg-logger-fc

Enable

// config/plugin.js
exports.loggerFC = {
  enable: true,
  package: 'egg-logger-fc',
};

With zero config, business logs land in SLS as:

{"time":"2026-04-17T07:00:26.518Z","level":"INFO","pid":12,"hostname":"fc-xxx","msg":"[auth] login ok","logger":"logger","requestId":"1-abcdef","method":"POST","url":"/api/auth/session","ip":"10.0.0.1","userId":42,"useMs":34}

To slice what used to be separate log files, filter on logger:

• logger: logger — business logs (was <app>-web.log)
• logger: coreLogger — Egg framework core logs (was egg-web.log)
• logger: errorLogger — centralized errors (was common-error.log)
• logger: <name> — any config.customLogger[name] you declared

Configure

// config/config.default.js
exports.loggerFC = {
  // Default: 'x-fc-request-id' (FC 3.0 convention)
  requestIdHeader: 'x-fc-request-id',

  // Optional: merge extra fields into every request-scoped log line.
  // Must return a plain object. Thrown errors are swallowed so that a
  // broken config never breaks request handling.
  extraFields: ctx => ({
    traceId: ctx.get('x-trace-id'),
    tenantId: ctx.state.tenantId,
  }),
};

Log level

Set ALIYUN_FC_LOG_LEVEL (FC's standard env var) to debug / info / warn / error. The plugin maps it to the console transport's level on every logger.

Advanced: using the transport directly

If you want the transport without the auto-configuration (e.g. to attach it to a custom logger), import it:

const { JsonStdoutTransport } = require('egg-logger-fc');

app.getLogger('auditLogger').set('console', new JsonStdoutTransport({
  name: 'auditLogger', // becomes the `logger` field in every emitted JSON line
  level: 'INFO',
  localStorage: app.ctxStorage,
  requestIdHeader: 'x-fc-request-id',
  extraFields: ctx => ({ userId: ctx.state.user?.id }),
}));

License

MIT