Setting up private registry in Docker - Try It Yourself

Setting up a Private Docker Registry

📖 Scenario: You are working in a small company that wants to store Docker images privately to share them securely among team members. You will set up a private Docker registry on your local machine to host images without using public registries.

🎯 Goal: Build a private Docker registry container, tag an image to push to it, push the image, and verify it is stored in your private registry.

📋 What You'll Learn

Create a Docker container running the official registry image

Tag the hello-world image to point to your private registry

Push the tagged image to your private registry

List images in your private registry to confirm the push

💡 Why This Matters

🌍 Real World

Companies often use private Docker registries to store and share container images securely within their network without exposing them publicly.

💼 Career

Knowing how to set up and manage private registries is essential for DevOps engineers to maintain secure and efficient container workflows.

1

Start a private Docker registry container

Run a Docker container named my-registry using the official registry:2 image. Map the container port 5000 to the host port 5000 so you can access the registry locally.

Docker

# Run the Docker registry container
# Your code here

Hint

Use docker run -d -p 5000:5000 --name my-registry registry:2 to start the registry container in detached mode.

2

Tag the hello-world image for your private registry

Tag the existing hello-world image with the new name localhost:5000/hello-world so it points to your private registry on your local machine.

Docker

docker run -d -p 5000:5000 --name my-registry registry:2
# Tag the hello-world image for your private registry
# Your code here

Hint

Use docker tag hello-world localhost:5000/hello-world to create the new tag.

3

Push the tagged image to your private registry

Push the image tagged as localhost:5000/hello-world to your private registry running on port 5000.

Docker

docker tag hello-world localhost:5000/hello-world
# Push the tagged image to your private registry
# Your code here

Hint

Use docker push localhost:5000/hello-world to upload the image to your registry.

4

Verify the image is stored in your private registry

Run a command to list the repositories in your private registry by querying the registry API at http://localhost:5000/v2/_catalog. Use curl to get the list and print it.

Docker

docker push localhost:5000/hello-world
# Use curl to list repositories in the private registry
# Your code here

Hint

Use curl http://localhost:5000/v2/_catalog to see the list of images stored in your registry.

Practice

1. What is the main purpose of setting up a private Docker registry?

easy

A. To automatically update Docker images from Docker Hub

B. To speed up Docker container execution

C. To store Docker images securely within your own network

D. To monitor running Docker containers

Solution

1. Step 1: Understand what a Docker registry does

   A Docker registry stores Docker images so they can be shared and reused.

2. Step 2: Identify the benefit of a private registry

   A private registry keeps images secure and accessible only within your network.

3. Final Answer:

   To store Docker images securely within your own network -> Option C

4. Quick Check:

   Private registry = secure image storage [OK]

Hint: Private registry means secure image storage inside your network [OK]

Common Mistakes:

• Confusing registry with container runtime
• Thinking it speeds up container execution
• Assuming it automatically updates images

2. Which command correctly starts a private Docker registry on port 5000?

easy

A. docker start registry -p 5000:5000

B. docker build -t registry:5000 .

C. docker create registry -p 5000:5000

D. docker run -d -p 5000:5000 --name registry registry:2

Solution

1. Step 1: Identify the correct Docker command to run a container

   The command to start a container is 'docker run' with port mapping.

2. Step 2: Check the syntax for running the registry image

   docker run -d -p 5000:5000 --name registry registry:2 uses 'docker run -d -p 5000:5000 --name registry registry:2' which is correct.

3. Final Answer:

   docker run -d -p 5000:5000 --name registry registry:2 -> Option D

4. Quick Check:

   Run container with port 5000 mapped = docker run -d -p 5000:5000 --name registry registry:2 [OK]

Hint: Use 'docker run -d -p 5000:5000' to start registry container [OK]

Common Mistakes:

• Using 'docker start' instead of 'docker run'
• Confusing 'docker create' with 'docker run'
• Trying to build instead of run the registry image

3. After running a private registry on localhost:5000, what is the correct command to tag an image named myapp for pushing to this registry?

medium

A. docker tag myapp localhost:5000/myapp

B. docker push myapp localhost:5000/myapp

C. docker tag localhost:5000/myapp myapp

D. docker run myapp localhost:5000/myapp

Solution

1. Step 1: Understand tagging for private registry

   To push an image to a private registry, you must tag it with the registry address first.

2. Step 2: Identify the correct tag command

   docker tag myapp localhost:5000/myapp uses 'docker tag myapp localhost:5000/myapp' which correctly tags the image.

3. Final Answer:

   docker tag myapp localhost:5000/myapp -> Option A

4. Quick Check:

   Tag image with registry address before push = docker tag myapp localhost:5000/myapp [OK]

Hint: Tag image as 'localhost:5000/name' before pushing [OK]

Common Mistakes:

• Trying to push without tagging first
• Reversing tag source and target
• Using 'docker run' instead of 'docker tag'

4. You tried to push an image to your private registry but got an error: denied: requested access to the resource is denied. What is the most likely cause?

medium

A. The registry container is not running

B. The image was not tagged with the private registry address

C. Docker daemon is not installed

D. The image name contains invalid characters

Solution

1. Step 1: Understand the error meaning

   The error means Docker cannot find the image at the specified registry path.

2. Step 2: Check tagging before pushing

   If the image is not tagged with the private registry address, push will fail with this error.

3. Final Answer:

   The image was not tagged with the private registry address -> Option B

4. Quick Check:

   Push denied = missing correct tag [OK]

Hint: Check if image is tagged with registry address before push [OK]

Common Mistakes:

• Assuming registry container is stopped without checking
• Thinking Docker daemon is missing
• Blaming image name format without evidence

5. You want to secure your private Docker registry with TLS. Which of these steps is necessary to enable HTTPS access?

hard

A. Mount your TLS certificate and key into the registry container and configure the registry to use them

B. Run the registry container with the --tls flag without any certificates

C. Tag images with https:// prefix before pushing

D. Use Docker Hub instead of a private registry

Solution

1. Step 1: Understand TLS setup for private registry

   To enable HTTPS, the registry needs valid TLS certificates mounted and configured.

2. Step 2: Identify correct method to provide TLS certs

   Mounting the certificate and key files into the container and configuring the registry is required.

3. Final Answer:

   Mount your TLS certificate and key into the registry container and configure the registry to use them -> Option A

4. Quick Check:

   TLS requires certs mounted and configured [OK]

Hint: Mount TLS certs into registry container for HTTPS [OK]

Common Mistakes:

• Expecting a --tls flag to work without certs
• Tagging images with https:// prefix
• Using Docker Hub instead of securing private registry