Deploy an app with Docker

Docker isolates your application and its dependencies in a reproducible container. You run an image, map ports and volumes, and you are done.

Cause / The problem

“It works on my machine” is the classic problem: a different runtime version, a missing system dependency, a port already taken. Docker removes these gaps by packaging the app with its environment.

Solution

1. Install Docker on your instance:

   curl -fsSL https://get.docker.com | sh
   sudo usermod -aG docker $USER   # then log out and back in

2. Run an existing image:

   docker run -d --name my-app -p 8080:8080 -e PORT=8080 my-image:latest

   • -d: detached, --name: container name.
   • -p host:container: map a port, -e KEY=value: an env var.
   • -v /host/path:/container/path: a persistent volume.
3. Check the status:

   docker ps                  # running containers
   docker logs -f my-app      # live logs

4. Build your own image with a Dockerfile, then:

   docker build -t my-app .
   docker run -d -p 8080:8080 my-app

5. Use docker-compose to manage several services. docker-compose.yml:

   services:
     app:
       image: my-app:latest
       ports: ["8080:8080"]
       environment:
         PORT: "8080"
       volumes: ["./data:/app/data"]
       restart: unless-stopped

   Then docker compose up -d.
6. Pick a restart policy: restart: unless-stopped or restart: always to survive a reboot.
7. Update:

   docker compose pull && docker compose up -d

Common errors: bind: address already in use (a port is taken — change the host port), permission denied (add your user to the docker group or use sudo).