GitHub Actions with Docker - Step-by-Step Execution

Process Flow - GitHub Actions with Docker

Push code to GitHub

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GitHub Actions triggered

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Run workflow steps

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Build Docker image

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Run tests inside Docker container

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Push Docker image to registry (optional)

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Complete workflow

This flow shows how pushing code triggers GitHub Actions to build and test a Docker image, then optionally push it to a registry.

Execution Sample

Docker

name: Docker CI
on: [push]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Build Docker image
        run: docker build -t myapp:latest .
      - name: Run tests
        run: docker run myapp:latest pytest

This GitHub Actions workflow builds a Docker image and runs tests inside the container on every push.

Process Table

Step	Action	Command Run	Result	Next Step
1	Trigger workflow	Push code to GitHub	Workflow starts	Checkout code
2	Checkout code	actions/checkout@v3	Code available on runner	Build Docker image
3	Build Docker image	docker build -t myapp:latest .	Docker image 'myapp:latest' created	Run tests in container
4	Run tests	docker run myapp:latest pytest	Tests executed, results shown	Workflow complete
5	Complete workflow	N/A	Workflow ends successfully	End

💡 Workflow ends after tests run successfully or fails if any step errors

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
Code	Not checked out	Checked out on runner	Checked out on runner	Checked out on runner	Checked out on runner
Docker Image	Not built	Not built	Built as 'myapp:latest'	Built as 'myapp:latest'	Built as 'myapp:latest'
Test Status	Not run	Not run	Not run	Tests passed or failed	Tests passed or failed

Key Moments - 3 Insights

Why do we need to checkout the code before building the Docker image?

The checkout step downloads the code to the runner so the docker build command can access the Dockerfile and source files. Without it, the build would fail (see execution_table step 2).

What happens if the tests inside the Docker container fail?

If tests fail during the 'docker run' step (step 4), the workflow stops and marks the run as failed. This prevents pushing broken code.

Can the Docker image be pushed to a registry in this workflow?

Yes, but this example does not include that step. You can add a step after tests to push the image if tests pass.

Visual Quiz - 3 Questions

Look at the execution table, what is the result after step 3?

A Code is checked out on the runner

B Docker image 'myapp:latest' is created

C Tests have been executed

D Workflow ends successfully

💡 Hint

Check the 'Result' column for step 3 in the execution_table

At which step does the workflow run tests inside the Docker container?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look for the 'Run tests' action in the execution_table

If the checkout step is removed, what will happen during the Docker build?

A Docker build fails due to missing files

B Docker image builds successfully

C Tests run without errors

D Workflow completes without building

💡 Hint

Refer to key_moments about why checkout is needed before build

Concept Snapshot

GitHub Actions with Docker:
- Trigger on push event
- Checkout code to runner
- Build Docker image with 'docker build'
- Run tests inside container with 'docker run'
- Optionally push image to registry
- Workflow stops if any step fails

Full Transcript

This visual execution shows how GitHub Actions automates Docker workflows. When code is pushed, the workflow starts by checking out the code to the runner. Then it builds a Docker image using the Dockerfile in the repo. After building, it runs tests inside a container created from that image. If tests pass, the workflow completes successfully. If any step fails, the workflow stops and reports failure. This process helps automate testing and deployment using Docker containers in GitHub Actions.