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

Process Flow - Building Docker images in pipeline

Start Pipeline

↓

Checkout Code

↓

Run Docker Build

↓

Tag Docker Image

↓

Push Image to Registry

↓

End Pipeline

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

Execution Sample

Jenkins

pipeline {
  agent any
  stages {
    stage('Build Docker Image') {
      steps {
        script {
          docker.build('myapp:latest')
        }
      }
    }
  }
}

This Jenkins pipeline builds a Docker image named 'myapp:latest' from the current directory.

Process Table

Step	Action	Command Run	Result	Next Step
1	Start Pipeline	N/A	Pipeline started	Checkout Code
2	Checkout Code	git checkout	Code downloaded	Run Docker Build
3	Run Docker Build	docker build -t myapp:latest .	Docker image 'myapp:latest' built	Tag Docker Image
4	Tag Docker Image	docker tag myapp:latest registry/myapp:latest	Image tagged for registry	Push Image to Registry
5	Push Image to Registry	docker push registry/myapp:latest	Image pushed to registry	End Pipeline
6	End Pipeline	N/A	Pipeline finished successfully	N/A

💡 Pipeline ends after pushing the Docker image to the registry.

Status Tracker

Variable	Start	After Step 3	After Step 4	After Step 5	Final
docker_image	none	myapp:latest (built)	registry/myapp:latest (tagged)	registry/myapp:latest (pushed)	registry/myapp:latest (available in registry)

Key Moments - 3 Insights

Why do we tag the Docker image after building it?

Tagging the image (see Step 4) prepares it with the correct name for the registry so it can be pushed and identified properly.

What happens if the docker build command fails?

If the build fails at Step 3, the pipeline stops and does not proceed to tagging or pushing, preventing broken images from being pushed.

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

The Docker build uses the code files as context, so checking out the code (Step 2) ensures the latest files are available for the image.

Visual Quiz - 3 Questions

Look at the execution table, what is the docker_image variable value after Step 4?

A myapp:latest (built)

B registry/myapp:latest (tagged)

C registry/myapp:latest (pushed)

D none

💡 Hint

Check variable_tracker column 'After Step 4' for docker_image value.

At which step does the pipeline push the Docker image to the registry?

A Step 5

B Step 4

C Step 3

D Step 6

💡 Hint

Look at the 'Action' and 'Command Run' columns in execution_table for pushing.

If the checkout code step is skipped, what will likely happen during the Docker build?

A Docker build will succeed with latest code

B Docker image will be pushed without building

C Docker build will fail or build old code

D Pipeline will skip to tagging

💡 Hint

Refer to key_moments about why checkout is needed before build.

Concept Snapshot

Jenkins pipeline builds Docker images by:
1. Checking out code
2. Running 'docker build' to create image
3. Tagging image for registry
4. Pushing image to registry
Each step must succeed to continue pipeline.

Full Transcript

This Jenkins pipeline example shows how to build a Docker image in a CI/CD process. It starts by checking out the source code from version control. Then it runs the docker build command to create an image named 'myapp:latest'. After building, it tags the image with the registry path to prepare for pushing. Finally, it pushes the tagged image to the Docker registry. The pipeline ends successfully after the push. Variables like the docker_image name change as the image is built, tagged, and pushed. If any step fails, the pipeline stops to avoid pushing incomplete images.