Skip to main content

Zero-Downtime Deployments

Every deployment involves replacing the running version of your application with a new one. This guide covers how Appliku handles deployments and what you can do to minimize downtime.

How Appliku Handles Deployments​

Server Mode​

In server mode, Appliku deploys by stopping the old container and starting the new one. There is a brief period of downtime while the new container starts up and becomes ready to serve traffic.

Cluster Mode (Docker Swarm)​

In cluster mode, Appliku uses Docker Swarm's rolling update mechanism. Swarm starts new containers before stopping old ones, routing traffic to healthy instances throughout the process. This provides true zero-downtime deployments.

tip

If zero-downtime deployments are critical for your application, consider using cluster mode with Docker Swarm. It handles rolling updates automatically.

Tips for Reducing Downtime​

Even in server mode, you can significantly reduce deployment downtime:

1. Optimize Startup Time​

The faster your application starts, the shorter the downtime window. Common strategies:

  • Minimize the work done at application startup
  • Use lightweight base images
  • Pre-compile assets during the build phase, not at startup
  • Avoid running database queries during startup

2. Use a Release Command​

Run database migrations and other pre-deployment tasks using a release command. This runs before the new containers start serving traffic:

python manage.py migrate --noinput

Configure the release command in your application's Build Settings. This ensures migrations complete before the container swap happens.

3. Handle Graceful Shutdown​

Make sure your application handles SIGTERM signals properly. When Appliku stops the old container, it sends SIGTERM first, giving your application time to finish in-flight requests before SIGKILL.

For Gunicorn, set a graceful timeout:

gunicorn myproject.wsgi --graceful-timeout 30

4. Keep Migrations Backward-Compatible​

Write database migrations that work with both the old and new versions of your code. This is especially important for cluster mode where old and new containers run simultaneously:

  • Add new columns as nullable or with defaults
  • Deploy the column addition first, then the code that uses it
  • Remove old columns only after the code no longer references them
note

Backward-compatible migrations are a best practice regardless of your deployment strategy. They prevent errors if a deployment needs to be rolled back.

5. Use Health Checks​

Configure health check endpoints so Appliku can verify your application is ready to serve traffic before routing requests to it.

A simple health check endpoint in Django:

# urls.py
from django.http import JsonResponse

def health_check(request):
    return JsonResponse({"status": "ok"})

urlpatterns = [
    # ...
    path("health/", health_check),
]