Why Docker image as artifact in Jenkins? - Purpose & Use Cases

The Big Idea

What if you could package your app once and run it anywhere without surprises?

The Scenario

Imagine you build your app on one computer, then try to run it on another. You copy files manually, hoping all settings and dependencies match perfectly.

The Problem

This manual copying is slow and risky. Different environments cause errors. You waste time fixing issues that could have been avoided.

The Solution

Using a Docker image as an artifact packages your app with everything it needs. You build once, then share the image everywhere. It runs the same on any machine.

Before vs After

✗ Before

scp -r app_files user@server:/app
ssh user@server 'cd /app && ./run_app.sh'

✓ After

docker build -t myapp:latest .
docker tag myapp:latest myrepo/myapp:latest
docker push myrepo/myapp:latest
ssh user@server 'docker pull myrepo/myapp:latest && docker run myrepo/myapp:latest'

What It Enables

You can deliver consistent, reliable applications anywhere, saving time and avoiding frustrating environment problems.

Real Life Example

A developer builds a web app image once, then the operations team deploys it on multiple servers without worrying about missing dependencies or config differences.

Key Takeaways

Manual copying causes errors and wastes time.

Docker images bundle app and environment together.

Images as artifacts ensure consistent deployment everywhere.

Practice

1. What is the main reason to save a Docker image as an artifact in Jenkins?

easy

A. To run the image on a different operating system

B. To delete the image after the build

C. To convert the image into a container

D. To reuse the image later without rebuilding it

Solution

1. Step 1: Understand Docker image reuse

   Saving a Docker image as an artifact allows you to reuse it later without rebuilding, saving time and resources.

2. Step 2: Identify Jenkins artifact purpose

   Jenkins artifacts store files from builds for later use or sharing, perfect for Docker images.

3. Final Answer:

   To reuse the image later without rebuilding it -> Option D

4. Quick Check:

   Docker image reuse = To reuse the image later without rebuilding it [OK]

Hint: Artifacts store files to reuse later, like saving your work [OK]

Common Mistakes:

• Thinking artifacts delete images
• Confusing image with container
• Assuming artifacts change OS compatibility

2. Which Jenkins pipeline step correctly archives a saved Docker image file named myimage.tar?

easy

A. archiveArtifacts artifacts: 'myimage.tar'

B. archiveArtifacts file: 'myimage.tar'

C. archiveArtifact artifacts: 'myimage.tar'

D. archiveArtifacts files: 'myimage.tar'

Solution

1. Step 1: Recall Jenkins archiveArtifacts syntax

   The correct syntax uses the parameter name 'artifacts' to specify files to archive.

2. Step 2: Match correct parameter and spelling

   archiveArtifacts artifacts: 'myimage.tar' uses 'archiveArtifacts artifacts: 'myimage.tar'', which is correct syntax.

3. Final Answer:

   archiveArtifacts artifacts: 'myimage.tar' -> Option A

4. Quick Check:

   Correct parameter is 'artifacts' = archiveArtifacts artifacts: 'myimage.tar' [OK]

Hint: Use 'artifacts' parameter exactly in archiveArtifacts step [OK]

Common Mistakes:

• Using 'file' instead of 'artifacts'
• Misspelling 'archiveArtifacts'
• Using singular 'archiveArtifact'

3. Given this Jenkins pipeline snippet:

stage('Save Image') {
  steps {
    sh 'docker save myapp:latest -o myapp.tar'
    archiveArtifacts artifacts: 'myapp.tar'
  }
}

What will Jenkins do after this stage completes?

medium

A. Delete the Docker image myapp:latest

B. Save the Docker image as a file and archive it as a build artifact

C. Run the Docker container from the saved image

D. Build a new Docker image named myapp:latest

Solution

1. Step 1: Analyze docker save command

   The command 'docker save myapp:latest -o myapp.tar' saves the Docker image to a file named myapp.tar.

2. Step 2: Understand archiveArtifacts usage

   The 'archiveArtifacts' step archives the saved file as a Jenkins build artifact for later use.

3. Final Answer:

   Save the Docker image as a file and archive it as a build artifact -> Option B

4. Quick Check:

   docker save + archiveArtifacts = Save the Docker image as a file and archive it as a build artifact [OK]

Hint: docker save creates file; archiveArtifacts stores it [OK]

Common Mistakes:

• Confusing save with build
• Thinking it runs containers
• Assuming image is deleted

4. You wrote this Jenkins pipeline snippet:

sh 'docker save myapp:latest -o myapp.tar'
archiveArtifacts file: 'myapp.tar'

Why does Jenkins fail to archive the Docker image file?

medium

A. Because 'docker save' does not create a file

B. Because the image name is incorrect

C. Because the parameter name should be 'artifacts', not 'file'

D. Because archiveArtifacts cannot archive .tar files

Solution

1. Step 1: Check archiveArtifacts parameter

   The correct parameter to specify files is 'artifacts', not 'file'. Using 'file' causes failure.

2. Step 2: Confirm docker save output

   'docker save' correctly creates the file 'myapp.tar', so the problem is not with the file creation.

3. Final Answer:

   Because the parameter name should be 'artifacts', not 'file' -> Option C

4. Quick Check:

   Parameter must be 'artifacts' = Because the parameter name should be 'artifacts', not 'file' [OK]

Hint: Use 'artifacts' parameter exactly in archiveArtifacts step [OK]

Common Mistakes:

• Using 'file' instead of 'artifacts'
• Assuming docker save fails silently
• Thinking archiveArtifacts rejects .tar files

5. You want to reuse a Docker image saved as appimage.tar from a previous Jenkins build artifact in a new pipeline. Which sequence correctly loads and runs the image?

hard

A. sh 'docker load -i appimage.tar'
sh 'docker run appimage:latest'

B. sh 'docker run -i appimage.tar'
sh 'docker load appimage:latest'

C. sh 'docker save -i appimage.tar'
sh 'docker run appimage:latest'

D. sh 'docker load appimage.tar'
sh 'docker run appimage:latest'

Solution

1. Step 1: Understand docker load syntax

   To load an image from a file, use 'docker load -i filename'. This imports the image into Docker.

2. Step 2: Run the loaded image

   After loading, run the image by its tag, e.g., 'docker run appimage:latest'.

3. Final Answer:

   sh 'docker load -i appimage.tar' sh 'docker run appimage:latest' -> Option A

4. Quick Check:

   Load with '-i', then run by tag = sh 'docker load -i appimage.tar' sh 'docker run appimage:latest' [OK]

Hint: Load with 'docker load -i', then run image by tag [OK]

Common Mistakes:

• Using 'docker run' with file instead of image tag
• Confusing 'docker save' with 'docker load'
• Omitting '-i' option in docker load