Monitor container output, debug errors, and track application behavior with real-time log streaming.

What are Container Logs?

Container logs capture all output from your Docker container:

What’s captured:

  • ✅ stdout — Standard output (console.log, print, echo)
  • ✅ stderr — Error output (exceptions, warnings)
  • ✅ Docker daemon — Container lifecycle events
  • ✅ Application logs — Your application’s log output

Not captured:

  • ❌ Logs written to files inside the container (unless volume-mounted)
  • ❌ Historical logs before streaming started

Accessing Container Logs

  1. Open the container detail page
  2. Click the Logs tab

Streaming Logs

Logs don’t stream automatically — you must start them manually.

Click Start Stream to open a WebSocket connection. The button changes to Stop Stream once connected and logs start appearing in real-time.

Toggle Auto-scroll to keep the latest logs in view as they arrive. Scroll up manually to pause auto-scroll and read earlier entries.

Click Download to save all currently visible logs to a .txt file — useful for offline analysis, sharing with teammates, or grepping locally.

Log Entry Format

Each entry follows this format:

  [YYYY-MM-DD HH:MM:SS.mmm] [stream] message

Example:

  [2025-12-18 14:30:45.123] [stdout] Starting Nginx 1.25.3
[2025-12-18 14:30:45.234] [stdout] Listening on port 80
[2025-12-18 14:31:22.456] [stderr] Error: Database connection failed
[2025-12-18 14:31:22.567] [stderr]   at connect (db.js:45:10)
  • stdout — normal text
  • stderr — shown in red

Timestamps are displayed in your local browser timezone.

Common Log Patterns

Nginx 

  [stdout] 2025/12/18 14:30:45 [notice] nginx/1.25.3
[stdout] 2025/12/18 14:30:45 [notice] start worker process 29
[stdout] 172.16.0.1 - - [18/Dec/2025:14:32:15 +0000] "GET / HTTP/1.1" 200 615

PostgreSQL 

  [stdout] 2025-12-18 14:30:50 UTC [1] LOG:  starting PostgreSQL 15.3
[stdout] 2025-12-18 14:30:50 UTC [1] LOG:  listening on IPv4 address "0.0.0.0", port 5432
[stdout] 2025-12-18 14:30:50 UTC [1] LOG:  database system is ready to accept connections

Node.js 

  [stdout] Connecting to database...
[stdout] Database connected successfully
[stdout] Listening on port 3000
[stdout] GET /api/users 200 45ms
[stderr] Warning: Deprecated API usage

Error with stack trace 

  [stderr] Error: Connection timeout
[stderr]   at Timeout._onTimeout (/app/lib/db.js:123:15)
[stderr]   at listOnTimeout (node:internal/timers:559:17)
[stderr] Application shutting down due to fatal error

Debugging with Logs

Container starts then immediately stops

  1. Open the Logs tab and click Start Stream before restarting the container
  2. Look for red stderr entries near the top
  3. Common startup errors:
      [stderr] Error: POSTGRES_PASSWORD must be set
[stderr] Error: bind EADDRINUSE 0.0.0.0:3000
[stderr] Error: Cannot find module 'express'
  4. Fix the configuration and restart

Finding a specific past error

  • Click Download, then open the file in a text editor and use Ctrl+F
  • Or use browser search (Ctrl+F) directly in the log viewer

Application is slow

Compare timestamps between related log lines to find the delay:

  [stdout] [14:30:00.000] Database query started
[stdout] [14:30:05.456] Database query completed   ← 5.4s!

Add timing logs to narrow it down further:

  const start = Date.now();
const result = await db.query(...);
console.log(`[PERF] Query completed in ${Date.now() - start}ms`);

Troubleshooting

Streaming but no logs appear

  • The application may log to files instead of stdout — configure it to use stdout/stderr
  • The container may have just started — wait a moment and trigger some activity
  • Log level may be set too high — set it to INFO or DEBUG

Stream disconnects unexpectedly

  1. Click Start Stream again to reconnect
  2. Verify the container is still in Running state
  3. Check for network interruptions — refresh the page and restart the stream
  4. Open browser DevTools → Network → WS to look for WebSocket errors

Too many logs scrolling too fast

  • Disable Auto-scroll and scroll to the section you need
  • Click Stop Stream, read what’s there, then resume
  • Download the logs and filter with your editor

Best Practices

Log to stdout/stderr — not to files:

  // Good
console.log("User logged in:", userId);
console.error("Login failed:", error);

// Bad - won't appear in logs tab
fs.appendFileSync('/var/log/app.log', message);

Include context in log messages:

  console.error("Payment failed:", { userId, amount, error: err.message });

Use log levels to control verbosity:

  if (process.env.LOG_LEVEL === 'debug') {
  console.log('Debug: detailed info');
}

Stop streaming when you’re done debugging to reduce bandwidth and browser memory usage.

Quick Reference

ControlAction
Start StreamBegin WebSocket log streaming
Stop StreamClose WebSocket connection
Auto-scrollToggle automatic scroll to bottom
DownloadSave visible logs to a text file

Next Steps