Fly.io Events & Monitoring

Overview

Fly.io does not have traditional webhooks. Instead, monitor machine state changes via the Machines API, process structured logs via fly logs, and use health check endpoints for automated responses.

Instructions

Step 1: Poll Machine State Changes

// Monitor machine state transitions via Machines API
async function watchMachines(appName: string, callback: (event: MachineEvent) => void) {
  const client = new FlyClient(appName, process.env.FLY_API_TOKEN!);
  const stateCache = new Map<string, string>();

  setInterval(async () => {
    const machines = await client.listMachines();
    for (const m of machines) {
      const prev = stateCache.get(m.id);
      if (prev && prev !== m.state) {
        callback({
          machineId: m.id,
          region: m.region,
          previousState: prev,
          currentState: m.state,
          timestamp: new Date(),
        });
      }
      stateCache.set(m.id, m.state);
    }
  }, 10_000);  // Check every 10 seconds
}

interface MachineEvent {
  machineId: string;
  region: string;
  previousState: string;
  currentState: string;
  timestamp: Date;
}

Step 2: Health Check Event Handler

// Implement health check that reports machine health
// Fly.io uses this to auto-restart unhealthy machines

import express from 'express';
const app = express();

app.get('/health', async (req, res) => {
  const checks = {
    database: await checkPostgres(),
    redis: await checkRedis(),
    memory: process.memoryUsage().heapUsed < 500 * 1024 * 1024,  // < 500MB
  };

  const healthy = Object.values(checks).every(Boolean);
  res.status(healthy ? 200 : 503).json({
    status: healthy ? 'healthy' : 'unhealthy',
    region: process.env.FLY_REGION,
    machine: process.env.FLY_MACHINE_ID,
    checks,
  });
});

Step 3: Structured Log Processing

# Stream logs and process with jq
fly logs -a my-app --json | jq -c 'select(.level == "error")' | while read -r line; do
  echo "$line" >> errors.jsonl
  # Send to Slack, PagerDuty, etc.
done

# Search recent logs for specific patterns
fly logs -a my-app --no-tail | grep -i "error\|crash\|oom"

Step 4: Deployment Event Notifications

# Post-deploy notification in CI
fly deploy -a my-app && \
curl -X POST "$SLACK_WEBHOOK_URL" \
  -H "Content-Type: application/json" \
  -d "{\"text\": \"Deployed my-app to Fly.io. Status: $(fly status -a my-app --json | jq -r '.Status')\"}"

Resources

• Machines API
• Health Checks
• Fly Logs

Next Steps

For performance optimization, see flyio-performance-tuning.