Building images in CI pipeline in Docker - Step-by-Step Execution

Process Flow - Building images in CI pipeline

Start CI Pipeline

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Checkout Code

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Run Docker Build

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Build Image

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Tag Image

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Push Image to Registry

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End Pipeline

The CI pipeline starts by getting the code, then builds a Docker image, tags it, and pushes it to a registry.

Execution Sample

Docker

git checkout main

docker build -t myapp:latest .
docker tag myapp:latest registry.example.com/myapp:latest
docker push registry.example.com/myapp:latest

This code checks out the main branch, builds a Docker image, tags it for the registry, and pushes it.

Process Table

Step	Action	Command	Result
1	Checkout code	git checkout main	Code switched to main branch
2	Build Docker image	docker build -t myapp:latest .	Image 'myapp:latest' built successfully
3	Tag image for registry	docker tag myapp:latest registry.example.com/myapp:latest	Image tagged as 'registry.example.com/myapp:latest'
4	Push image to registry	docker push registry.example.com/myapp:latest	Image pushed to registry successfully
5	Pipeline complete	-	Docker image ready in registry

💡 Pipeline ends after image is pushed to the registry

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4
Code branch	none	main	main	main	main
Docker image	none	none	myapp:latest	registry.example.com/myapp:latest	registry.example.com/myapp:latest
Registry status	none	none	none	none	pushed

Key Moments - 3 Insights

Why do we tag the image before pushing it?

Tagging the image with the registry address (step 3) tells Docker where to push it. Without tagging, Docker won't know the destination.

What happens if the build fails at step 2?

If the build fails, the pipeline stops and the image is not created or pushed. This prevents pushing broken images.

Why do we checkout the code first?

Checking out the code (step 1) ensures the latest source files are used to build the image, so the image matches the current code.

Visual Quiz - 3 Questions

Look at the execution table, what is the Docker image name after step 2?

A registry.example.com/myapp:latest

B none

C myapp:latest

D main

💡 Hint

Check the 'Docker image' variable in variable_tracker after Step 2

At which step is the image pushed to the registry?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the 'Action' and 'Result' columns in the execution_table

If the code checkout fails at step 1, what happens next?

A The pipeline continues to build the image

B The pipeline stops and no image is built

C The image is tagged but not pushed

D The image is pushed without building

💡 Hint

Refer to key_moments about build failure and pipeline stopping

Concept Snapshot

Building images in CI pipeline:
1. Checkout code to get latest files
2. Build Docker image locally
3. Tag image with registry path
4. Push image to remote registry
5. Pipeline ends with image ready for deployment

Full Transcript

In a CI pipeline for building Docker images, the process starts by checking out the latest code from the repository. Then, the pipeline runs the docker build command to create an image from the Dockerfile and source code. After the image is built, it is tagged with the registry address so Docker knows where to push it. Finally, the image is pushed to the remote registry, making it available for deployment. If any step fails, the pipeline stops to avoid pushing incomplete or broken images.