Pushing images to registry in Jenkins - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of pushing a Docker image to a registry?

Pushing a Docker image to a registry stores the image in a central place so it can be shared and used by others or deployed on different machines.

intermediate

Which Jenkins plugin helps with Docker image building and pushing?

The 'Docker Pipeline' plugin allows Jenkins to build, tag, and push Docker images within pipeline scripts.

intermediate

What Jenkins pipeline step is used to push a Docker image to a registry?

The 'docker.withRegistry' block combined with 'docker.image.push()' is used to authenticate and push images to a Docker registry.

beginner

Why do you need to login to a Docker registry before pushing an image?

Logging in authenticates your Jenkins job with the registry, allowing it to upload images securely and preventing unauthorized access.

beginner

What is a common format for tagging Docker images before pushing?

Images are tagged with the registry URL, repository name, and version or 'latest', for example: 'myregistry.com/myapp:latest'.

Which Jenkins pipeline syntax is used to push a Docker image to a registry?

A docker.pull('myimage')

B sh('docker push myimage')

C docker.build('myimage').run()

D docker.withRegistry('https://registry.url', 'credentialsId') { docker.image('myimage').push() }

Option D shows the correct Jenkins pipeline syntax to authenticate and push an image to a registry.

Why is tagging a Docker image important before pushing?

A It identifies the image version and destination repository.

B It deletes the image after pushing.

C It compresses the image to save space.

D It runs the image automatically.

Tagging helps specify the image version and where it should be stored in the registry.

What does the 'docker.withRegistry' step do in Jenkins?

A Builds a Docker image.

B Logs into the Docker registry for pushing or pulling images.

C Deletes images from the registry.

D Runs a Docker container.

'docker.withRegistry' authenticates Jenkins with the registry to allow image push or pull.

Which credential type is typically used for Docker registry login in Jenkins?

A GPG key

B SSH key

C Username and password

D API token for GitHub

Docker registries usually require username and password credentials for login.

What happens if you try to push a Docker image without logging in to the registry?

A Push will fail due to authentication error.

B Image will push successfully without login.

C Image will be deleted locally.

D Jenkins will automatically login.

Without login, the registry rejects the push because it cannot verify permissions.

Explain the steps to push a Docker image to a registry using Jenkins pipeline.

Think about building, tagging, authenticating, and pushing.

Why is it important to use credentials securely when pushing images in Jenkins?

Consider security and best practices.

Practice

1. What is the main purpose of pushing a Docker image to a registry in Jenkins?

easy

A. To run the Docker image on the Jenkins server

B. To delete the local Docker image after building

C. To create a new Dockerfile automatically

D. To save the built image so it can be shared and deployed elsewhere

Solution

1. Step 1: Understand Docker image pushing

   Pushing an image uploads it to a registry so others can access it.

2. Step 2: Connect to Jenkins usage

   Jenkins automates this to share images for deployment or other jobs.

3. Final Answer:

   To save the built image so it can be shared and deployed elsewhere -> Option D

4. Quick Check:

   Pushing = Save and share image [OK]

Hint: Pushing means uploading image for sharing [OK]

Common Mistakes:

• Confusing push with running the image
• Thinking push deletes local images
• Assuming push creates Dockerfiles

2. Which Jenkins pipeline step correctly pushes a Docker image named myapp:latest to Docker Hub after login?

easy

A. sh 'docker push myapp:latest'

B. sh 'docker pull myapp:latest'

C. sh 'docker build myapp:latest'

D. sh 'docker run myapp:latest'

Solution

1. Step 1: Identify the push command

   To upload an image, the command is docker push followed by the image name and tag.

2. Step 2: Check other commands

   docker pull downloads, docker build creates, and docker run executes images.

3. Final Answer:

   sh 'docker push myapp:latest' -> Option A

4. Quick Check:

   Push uploads image [OK]

Hint: Push uses 'docker push' command [OK]

Common Mistakes:

• Using pull instead of push
• Confusing build with push
• Trying to run instead of push

3. Given this Jenkins pipeline snippet, what will be the output if the Docker login fails?

stage('Push Image') {
  steps {
    sh 'docker login -u user -p wrongpassword'
    sh 'docker push myapp:latest'
  }
}

medium

A. The image will be pushed anonymously

B. The push will succeed anyway

C. The push will fail because login failed

D. The pipeline will skip the push step

Solution

1. Step 1: Understand docker login failure effect

   If login fails, Docker does not authenticate, so push cannot succeed to a private registry.

2. Step 2: Check pipeline behavior

   Since login command fails, the push command will also fail due to lack of permissions.

3. Final Answer:

   The push will fail because login failed -> Option C

4. Quick Check:

   Failed login blocks push [OK]

Hint: Push needs successful login first [OK]

Common Mistakes:

• Assuming push works without login
• Thinking pipeline skips failed steps automatically
• Believing anonymous push is allowed

4. You have this Jenkins pipeline snippet but the image is not pushed. What is the error?

stage('Push') {
  steps {
    sh 'docker login -u user -p $PASSWORD'
    sh 'docker push myapp'
  }
}

medium

A. The login command syntax is incorrect

B. The image tag is missing in the push command

C. The password variable should be in double quotes

D. Docker push does not require login

Solution

1. Step 1: Check the push command syntax

   The push command must specify the image name with a tag, e.g., myapp:latest. Without a tag, it defaults to 'latest' but explicit is better.

2. Step 2: Verify other parts

   Login syntax is correct, password variable usage is valid in shell, and login is required before push.

3. Final Answer:

   The image tag is missing in the push command -> Option B

4. Quick Check:

   Push needs image:tag [OK]

Hint: Always specify image tag when pushing [OK]

Common Mistakes:

• Omitting image tag causes push issues
• Misusing environment variables in shell
• Skipping login before push

5. In a Jenkins pipeline, you want to push a Docker image to a private registry that requires login. Which sequence correctly automates this process?

hard

A. Login with credentials, tag image with registry URL, then push tagged image

B. Push image first, then login to registry, then tag image

C. Tag image without login, then push, then login after push

D. Login, push image without tagging, then tag image

Solution

1. Step 1: Understand Docker push workflow

   You must login first to authenticate, then tag the image with the registry URL to specify destination, then push the tagged image.

2. Step 2: Analyze options

   Options B, C, and D have wrong order causing push failures or wrong image pushed.

3. Final Answer:

   Login with credentials, tag image with registry URL, then push tagged image -> Option A

4. Quick Check:

   Login -> tag -> push [OK]

Hint: Login first, tag image, then push [OK]

Common Mistakes:

• Pushing before login
• Pushing untagged images to private registry
• Tagging after pushing