Cloudflare Workers Observability

Production-grade observability for Cloudflare Workers: logging, metrics, tracing, and alerting.

Quick Start

// Structured logging with context
export default {
  async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise<Response> {
    const requestId = crypto.randomUUID();
    const logger = createLogger(requestId, env);

    try {
      logger.info('Request received', { method: request.method, url: request.url });

      const result = await handleRequest(request, env);

      logger.info('Request completed', { status: result.status });
      return result;
    } catch (error) {
      logger.error('Request failed', { error: error.message, stack: error.stack });
      throw error;
    }
  }
};

// Simple logger factory
function createLogger(requestId: string, env: Env) {
  return {
    info: (msg: string, data?: object) => console.log(JSON.stringify({ level: 'info', requestId, msg, ...data, timestamp: Date.now() })),
    error: (msg: string, data?: object) => console.error(JSON.stringify({ level: 'error', requestId, msg, ...data, timestamp: Date.now() })),
    warn: (msg: string, data?: object) => console.warn(JSON.stringify({ level: 'warn', requestId, msg, ...data, timestamp: Date.now() })),
  };
}

Critical Rules

1. Always use structured JSON logging - Plain text logs are hard to parse and aggregate
2. Include request context - Request ID, method, path in every log entry
3. Never log sensitive data - Redact tokens, passwords, PII from logs
4. Use appropriate log levels - ERROR for failures, WARN for recoverable issues, INFO for operations
5. Sample high-volume logs - Use 1-10% sampling for request logs in production

Observability Components

Component	Purpose	When to Use