containerization-and-devops

Class 3 - Docker Engine API Interaction via Unix Socket

Objective

To interact directly with the Docker Engine REST API using curl and the Unix socket without relying on standard Docker CLI lifecycle commands.

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Environment

• Windows 11
• WSL Ubuntu 24.04
• Docker Engine running
• Communication via: /var/run/docker.sock

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Step 1 – Start WSL Environment

wsl

Launches Ubuntu inside Windows.

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Step 2 – Verify Docker Socket

ls -l /var/run/docker.sock

Confirms Docker socket exists and shows permission details.

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Step 3 – Test Docker API Connectivity

curl --unix-socket /var/run/docker.sock http://localhost/_ping

Expected Output: OK

Confirms Docker daemon is accessible via Unix socket.

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Step 4 – Check Docker Version via API

curl --unix-socket /var/run/docker.sock http://localhost/version

Returns Docker Engine details in JSON format.

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Step 5 – List Containers using Docker CLI

docker ps
docker ps -a

Displays running and stopped containers.

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Step 6 – List Containers via Docker API

curl --unix-socket /var/run/docker.sock "http://localhost/v1.44/containers/json"

curl --unix-socket /var/run/docker.sock "http://localhost/v1.44/containers/json?all=true"

Retrieves container information in JSON format.

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Step 7 – Pull Nginx Image via API

curl --unix-socket /var/run/docker.sock -X POST "http://localhost/v1.44/images/create?fromImage=nginx&tag=latest"

Downloads nginx image using Docker REST API.

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Step 8 – Create Container via API

curl --unix-socket /var/run/docker.sock -X POST -H "Content-Type: application/json" http://localhost/v1.44/containers/create?name=mynginx -d '{
  "Image": "nginx",
  "ExposedPorts": {
    "80/tcp": {}
  },
  "HostConfig": {
    "PortBindings": {
      "80/tcp": [
        { "HostPort": "8080" }
      ]
    }
  }
}'

Creates container named mynginx with port mapping 8080 to container port 80.

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Step 9 – Start Container via API

curl --unix-socket /var/run/docker.sock -X POST http://localhost/v1.44/containers/mynginx/start

Starts the created container.

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Step 10 – Stop Container via API

curl --unix-socket /var/run/docker.sock -X POST http://localhost/v1.44/containers/mynginx/stop

Stops the running container.

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Step 11 – Inspect Container via API

curl --unix-socket /var/run/docker.sock http://localhost/v1.44/containers/mynginx/json

Displays detailed container metadata including state, mounts, networking, and port bindings.

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Step 12 – Image Pull Detailed Output

Shows full layer download progress of nginx image via API.

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Result

Successfully accessed Docker Engine directly via its REST API and performed:

• Socket verification
• API connectivity test
• Version inspection
• Image pull
• Container creation
• Container start
• Container stop
• Container inspection

All operations were executed using HTTP requests over the Unix socket.

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Learning Outcome

• Docker CLI internally communicates with Docker daemon via REST API.
• Docker daemon can be accessed directly through /var/run/docker.sock.
• Full container lifecycle management can be performed using HTTP requests.

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