Pushing images to registry in Jenkins - Step-by-Step Execution

Process Flow - Pushing images to registry

Build Docker Image

↓

Tag Image with Registry URL

↓

Login to Registry

↓

Push Image to Registry

↓

Verify Push Success

↓

END

This flow shows the steps to build a Docker image, tag it for a registry, login, push it, and verify success in a Jenkins pipeline.

Execution Sample

Jenkins

pipeline {
  agent any
  stages {
    stage('Build & Push') {
      steps {
        sh 'docker build -t myapp:latest .'
        sh 'docker tag myapp:latest registry.example.com/myapp:latest'
        sh 'echo $REGISTRY_PASS | docker login registry.example.com -u $REGISTRY_USER --password-stdin'
        sh 'docker push registry.example.com/myapp:latest'
      }
    }
  }
}

This Jenkins pipeline builds a Docker image, tags it with the registry URL, logs in using environment variables, and pushes the image to the registry.

Process Table

Step	Command	Action	Result	Notes
1	sh 'docker build -t myapp:latest .'	Build image from Dockerfile	Image 'myapp:latest' created locally	Image ready for tagging
2	sh 'docker tag myapp:latest registry.example.com/myapp:latest'	Tag image with registry URL	Image tagged as 'registry.example.com/myapp:latest'	Tag links local image to remote name
3	sh 'echo $REGISTRY_PASS | docker login registry.example.com -u $REGISTRY_USER --password-stdin'	Authenticate to registry	Login successful	Non-interactive login using env vars; allows pushing images
4	sh 'docker push registry.example.com/myapp:latest'	Push image to registry	Image pushed successfully	Image now stored in remote registry
5	-	Verify push	Image available in registry	Push complete, image accessible remotely

💡 All steps completed successfully; image is now in the registry.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
Image	none	myapp:latest (local)	registry.example.com/myapp:latest (tagged)	registry.example.com/myapp:latest (tagged)	registry.example.com/myapp:latest (pushed)	registry.example.com/myapp:latest (pushed and available)
Login Status	not logged in	not logged in	not logged in	logged in	logged in	logged in

Key Moments - 3 Insights

Why do we need to tag the image before pushing?

Tagging links the local image to the remote registry name. Without tagging, Docker doesn't know where to push the image. See execution_table step 2.

What happens if login to the registry fails?

If login fails, the push command will not work because authentication is required. See execution_table step 3 for successful login.

Is the image available remotely immediately after build?

No, the image is only local after build. It becomes available remotely only after a successful push. See execution_table steps 1 and 4.

Visual Quiz - 3 Questions

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

A myapp:latest

B latest

C registry.example.com/myapp:latest

D registry.example.com/latest

💡 Hint

Check the 'Result' column in step 2 of the execution_table.

At which step does the system authenticate to the registry?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look for the 'docker login' command in the execution_table.

If the login fails, what will happen at step 4?

A Push will fail due to authentication error

B Image will push successfully anyway

C Image will be deleted locally

D Tagging will be undone

💡 Hint

Refer to key_moments about login failure and step 4 action.

Concept Snapshot

Pushing images to a registry in Jenkins:
1. Build image locally with 'sh "docker build"'.
2. Tag image with registry URL using 'sh "docker tag"'.
3. Login to registry with 'sh "docker login"' using env vars.
4. Push image using 'sh "docker push"'.
5. Verify image is available remotely.
Tagging and login are required before push.

Full Transcript

This lesson shows how to push Docker images to a remote registry using Jenkins pipeline steps. First, you build the image locally with 'sh "docker build"'. Then, you tag the image with the registry URL so Docker knows where to send it. Next, you login to the registry to authenticate using environment variables for security. After successful login, you push the image with 'sh "docker push"'. Finally, you verify the image is available in the registry. Tagging and login are essential steps before pushing. The execution table traces each sh command and its result step-by-step, and the variable tracker shows how the image tag and login status change. Common confusions include why tagging is needed and what happens if login fails. The quiz tests understanding of these steps.

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