Pushing images to registry in Docker - Mini Project: Build & Apply

Pushing images to registry

📖 Scenario: You are working on a small project where you need to share your Docker image with your team. To do this, you will push your Docker image to a remote registry so others can download and use it.

🎯 Goal: Learn how to tag a local Docker image and push it to a remote Docker registry step-by-step.

📋 What You'll Learn

Have Docker installed and running on your machine

Have a local Docker image named myapp with tag v1

Have access to a Docker registry (for example, Docker Hub) with username myusername

💡 Why This Matters

🌍 Real World

Developers often need to share their Docker images with teammates or deploy them to cloud services. Pushing images to a registry makes this easy.

💼 Career

Knowing how to push Docker images is a key skill for DevOps engineers, cloud engineers, and developers working with containerized applications.

1

Create a local Docker image

Create a local Docker image called myapp with tag v1 using the command docker build -t myapp:v1 .

Docker

# Run the command to build the Docker image
# Your code here

Hint

Make sure you run this command in the directory with your Dockerfile.

2

Tag the local image for the remote registry

Tag the local image myapp:v1 with the remote registry name myusername/myapp:v1 using the command docker tag myapp:v1 myusername/myapp:v1

Docker

docker build -t myapp:v1 .
# Tag the image for the remote registry
# Your code here

Hint

Use the docker tag command to add the remote registry prefix to your image.

3

Log in to the Docker registry

Log in to the Docker registry using the command docker login and enter your username myusername and password when prompted

Docker

docker build -t myapp:v1 .
docker tag myapp:v1 myusername/myapp:v1
# Log in to the Docker registry
# Your code here

Hint

Run docker login and enter your Docker Hub credentials when asked.

4

Push the tagged image to the registry

Push the tagged image myusername/myapp:v1 to the remote registry using the command docker push myusername/myapp:v1

Docker

docker build -t myapp:v1 .
docker tag myapp:v1 myusername/myapp:v1
docker login
# Push the image to the registry
# Your code here

Hint

Use docker push with the full image name including your username.

Practice

1.

What is the main purpose of the docker push command?

easy

A. Remove a Docker image from local storage

B. Download an image from a remote registry

C. Run a container from an image

D. Upload a local Docker image to a remote registry

Solution

1. Step 1: Understand the command purpose

   The docker push command is used to send a local image to a remote registry so others can access it.

2. Step 2: Compare options with command function

   Downloading images uses docker pull, running containers uses docker run, and removing images uses docker rmi. Only uploading matches docker push.

3. Final Answer:

   Upload a local Docker image to a remote registry -> Option D

4. Quick Check:

   Push means upload image [OK]

Hint: Push means upload your image to share it [OK]

Common Mistakes:

• Confusing push with pull (download)
• Thinking push runs containers
• Assuming push deletes images

2.

Which of the following is the correct syntax to push a Docker image named myapp with tag v1 to Docker Hub?

docker push ________

easy

A. myapp:v1

B. myapp

C. myapp:v1 latest

D. push myapp:v1

Solution

1. Step 1: Recall push command syntax

   The correct syntax is docker push [repository]:[tag]. The tag is required if not using default 'latest'.

2. Step 2: Analyze options

   myapp:v1 uses myapp:v1 which is correct. myapp misses the tag. myapp:v1 latest has extra word 'latest' which is invalid. push myapp:v1 repeats 'push' which is wrong.

3. Final Answer:

   myapp:v1 -> Option A

4. Quick Check:

   Push needs image name and tag [OK]

Hint: Use image name with tag like repo:tag [OK]

Common Mistakes:

• Omitting the tag when required
• Adding extra words after image name
• Repeating the push command inside

3.

Given the commands below, what will be the output of the docker push command?

docker tag myapp:latest myrepo/myapp:v2
docker push myrepo/myapp:v2

medium

A. Image pushed successfully to myrepo/myapp:v2

B. Error: image not found locally

C. Authentication required before push

D. Image pushed but with tag 'latest'

Solution

1. Step 1: Understand tagging and pushing

   The image myapp:latest is tagged as myrepo/myapp:v2, preparing it for push to myrepo registry.

2. Step 2: Predict push output

   Since the image is tagged correctly and assuming user is logged in, the push will succeed with a success message.

3. Final Answer:

   Image pushed successfully to myrepo/myapp:v2 -> Option A

4. Quick Check:

   Tag then push means success [OK]

Hint: Tag image with repo before push [OK]

Common Mistakes:

• Forgetting to tag image before push
• Not logging in to registry
• Assuming default tag is always 'latest'

4.

What is wrong with the following commands if the push fails?

docker push myapp:v1

Assuming myapp:v1 is a local image and the user wants to push to Docker Hub.

medium

A. The push command syntax is incorrect

B. Image is not tagged with the Docker Hub repository name

C. Docker daemon is not running

D. The image tag 'v1' is invalid

Solution

1. Step 1: Check image tagging for remote push

   To push to Docker Hub, the image must be tagged with the repository name like username/myapp:v1.

2. Step 2: Identify the cause of failure

   Since the image is only myapp:v1 without repo prefix, Docker Hub rejects the push.

3. Final Answer:

   Image is not tagged with the Docker Hub repository name -> Option B

4. Quick Check:

   Push needs repo prefix [OK]

Hint: Tag image with repo name before pushing [OK]

Common Mistakes:

• Trying to push without repo prefix
• Assuming push syntax is wrong
• Ignoring Docker daemon status

5.

You want to push a local image webapp:latest to a private registry at registry.example.com. Which sequence of commands is correct?

hard

A. docker login registry.example.comdocker push webapp:latest

B. docker push webapp:latestdocker login registry.example.com

C. docker login registry.example.comdocker tag webapp:latest registry.example.com/webapp:latestdocker push registry.example.com/webapp:latest

D. docker tag webapp:latest registry.example.com/webappdocker push webapp:latest

Solution

1. Step 1: Login to the private registry

   You must log in first to authenticate with registry.example.com.

2. Step 2: Tag the image with the registry URL

   Tag webapp:latest as registry.example.com/webapp:latest so Docker knows where to push.

3. Step 3: Push the tagged image to the registry

   Push the correctly tagged image to upload it to the private registry.

4. Final Answer:

   docker login registry.example.com docker tag webapp:latest registry.example.com/webapp:latest docker push registry.example.com/webapp:latest -> Option C

5. Quick Check:

   Login, tag with registry, then push [OK]

Hint: Login, tag with registry URL, then push [OK]

Common Mistakes:

• Pushing before login
• Not tagging with registry URL
• Pushing wrong image name