How to Use Docker in GitHub Actions: Simple Guide

To use docker in GitHub Actions, add steps in your workflow YAML file that run docker commands inside a job with runs-on set to a Linux runner. Use the actions/checkout action to get your code, then run docker build and docker run commands as needed.

Syntax

In GitHub Actions, you define jobs and steps in a YAML file. To use Docker, you typically:

• Set runs-on to a Linux runner that has Docker installed.
• Use actions/checkout to get your repository code.
• Run docker commands inside run steps.

Example syntax for a step running Docker commands:

yaml

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Build Docker image
        run: docker build -t my-image:latest .
      - name: Run Docker container
        run: docker run --rm my-image:latest

Example

This example workflow builds a Docker image from your repository's Dockerfile and runs a container that prints a message.

yaml

name: Docker Build and Run

on: [push]

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Build Docker image
        run: docker build -t hello-world-image .
      - name: Run Docker container
        run: docker run --rm hello-world-image

Output

Sending build context to Docker daemon  2.048kB
Step 1/2 : FROM alpine
 ---> a24bb4013296
Step 2/2 : CMD echo "Hello from Docker in GitHub Actions!"
 ---> Running in 123abc456def
Removing intermediate container 123abc456def
 ---> 789xyz123uvw
Successfully built 789xyz123uvw
Successfully tagged hello-world-image:latest

Hello from Docker in GitHub Actions!

Common Pitfalls

Common mistakes when using Docker in GitHub Actions include:

• Not using a Linux runner (ubuntu-latest) because Windows or Mac runners may not have Docker installed.
• Forgetting to check out the repository before building the Docker image.
• Not tagging the Docker image properly, causing confusion or overwriting.
• Running Docker commands without --rm on containers, which can leave stopped containers consuming space.

yaml

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Build without checkout (wrong)
        run: docker build -t my-image .

# Correct way:
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Build Docker image
        run: docker build -t my-image:latest .

Quick Reference

Tips for using Docker in GitHub Actions:

• Always use ubuntu-latest runner for Docker support.
• Use actions/checkout@v3 before Docker commands.
• Tag images clearly with versions or latest.
• Use docker run --rm to clean up containers automatically.
• Use multi-stage Dockerfiles to keep images small.

Key Takeaways

Use a Linux runner like ubuntu-latest to run Docker commands in GitHub Actions.

Always check out your code before building Docker images with actions/checkout.

Tag Docker images clearly to avoid confusion and overwriting.

Use --rm flag with docker run to automatically remove containers after execution.

Test your Docker commands locally before adding them to your workflow.