Pushing images to registry in Jenkins - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Jenkins pipeline step?

Consider this Jenkins pipeline snippet that pushes a Docker image to a registry:

stage('Push Image') {
  steps {
    script {
      docker.withRegistry('https://myregistry.example.com', 'registry-credentials') {
        def appImage = docker.build('myapp:latest')
        appImage.push()
      }
    }
  }
}

What will Jenkins output if the push is successful?

A Successfully pushed image myapp:latest to https://myregistry.example.com

B Error: No such image: myapp:latest

C Permission denied: failed to push image to registry

D Syntax error in Jenkinsfile at line 3

💡 Hint

Think about what Jenkins logs when a Docker image push succeeds inside docker.withRegistry.

When the image push succeeds, Jenkins logs a success message indicating the image name and registry URL.

❓ Configuration

intermediate

Which Jenkins credential type is required for pushing Docker images?

You want to push Docker images to a private registry from Jenkins. Which credential type should you configure in Jenkins to authenticate properly?

A SSH Username with private key

B Username with password

C Secret text

D Certificate

💡 Hint

Docker registries usually require a username and password for login.

Docker registries authenticate using username and password, so Jenkins credentials of type 'Username with password' are needed.

❓ Troubleshoot

advanced

Why does this Jenkins pipeline fail to push the image?

Given this Jenkins pipeline snippet:

stage('Push Image') {
  steps {
    script {
      def appImage = docker.build('myapp:latest')
      appImage.push()
    }
  }
}

The push step fails with an authentication error. What is the most likely cause?

A Missing <code>docker.withRegistry</code> block to provide registry credentials

B The image name 'myapp:latest' is invalid

C The Jenkinsfile syntax is incorrect

D Docker daemon is not running on the Jenkins agent

💡 Hint

Think about how Jenkins provides credentials to Docker commands.

Without docker.withRegistry, Jenkins does not pass credentials to Docker, causing authentication failure on push.

🔀 Workflow

advanced

What is the correct order of steps to push a Docker image in Jenkins?

Arrange these steps in the correct order to build and push a Docker image to a registry in Jenkins:

A 3,4,1,2

B 4,1,3,2

C 4,3,1,2

D 1,4,3,2

💡 Hint

Think about when authentication must happen relative to building and pushing.

You first define the image name and tag, then authenticate to the registry, then build the image, and finally push it.

✅ Best Practice

expert

Which practice improves security when pushing Docker images in Jenkins?

Which of the following practices best improves security when pushing Docker images to a registry in Jenkins pipelines?

A Store registry credentials as plain text environment variables in Jenkinsfile

B Push images without authentication to speed up the pipeline

C Hardcode registry username and password in the Dockerfile

D Use Jenkins credentials plugin to store and inject registry credentials securely

💡 Hint

Consider how Jenkins manages sensitive information securely.

Using Jenkins credentials plugin securely stores and injects sensitive data without exposing it in code or logs.

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