Setting up private registry in Docker - Visual Walkthrough

Process Flow - Setting up private registry

Start Docker Registry Container

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Docker Registry Runs Locally

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Tag Local Image with Registry Address

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Push Image to Private Registry

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Pull Image from Private Registry

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Use Image in Docker Environment

This flow shows starting a private Docker registry, tagging images, pushing them to the registry, and pulling them back for use.

Execution Sample

Docker

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

docker tag myapp localhost:5000/myapp

docker push localhost:5000/myapp

docker pull localhost:5000/myapp

Commands to start a private registry, tag an image, push it to the registry, and pull it back.

Process Table

Step	Command	Action	Result
1	docker run -d -p 5000:5000 --name registry registry:2	Start registry container	Registry container running on port 5000
2	docker tag myapp localhost:5000/myapp	Tag local image	Image 'myapp' tagged as 'localhost:5000/myapp'
3	docker push localhost:5000/myapp	Push image to registry	Image pushed to private registry at localhost:5000
4	docker pull localhost:5000/myapp	Pull image from registry	Image pulled from private registry
5	-	End	Private registry setup and image transfer complete

💡 All steps completed successfully; private registry is running and images are stored locally.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
registry_container	not running	running	running	running	running	running
image_tag	myapp	myapp	localhost:5000/myapp	localhost:5000/myapp	localhost:5000/myapp	localhost:5000/myapp
image_location	local only	local only	local and tagged for registry	pushed to registry	available locally	available locally

Key Moments - 3 Insights

Why do we tag the image with 'localhost:5000/myapp' before pushing?

Tagging with 'localhost:5000/myapp' tells Docker to push the image to the private registry running on localhost port 5000, as shown in step 2 of the execution table.

What happens if the registry container is not running before pushing?

If the registry container is not running (step 1), the push command in step 3 will fail because there is no registry to receive the image.

Does pulling the image from the private registry overwrite the local image?

Yes, pulling the image from the private registry (step 4) updates or adds the image locally tagged as 'localhost:5000/myapp', as tracked in the variable_tracker.

Visual Quiz - 3 Questions

Look at the execution table, what is the state of the registry container after step 1?

A Not running

B Running on port 5000

C Stopped

D Crashed

💡 Hint

Check the 'Result' column in row for step 1 in the execution_table.

At which step is the image tagged for the private registry?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column in the execution_table for tagging.

If the registry container was not running, what would happen at step 3?

A Push would fail

B Image would push successfully

C Image would be deleted

D Image would be pulled instead

💡 Hint

Refer to key_moments about registry container state and push command.

Concept Snapshot

Setting up a private Docker registry:
1. Run registry container: docker run -d -p 5000:5000 --name registry registry:2
2. Tag image: docker tag myapp localhost:5000/myapp
3. Push image: docker push localhost:5000/myapp
4. Pull image: docker pull localhost:5000/myapp
This allows storing and sharing images locally without Docker Hub.

Full Transcript

To set up a private Docker registry, first run the registry container on your machine using 'docker run -d -p 5000:5000 --name registry registry:2'. This starts a registry listening on port 5000. Next, tag your local image with the registry address using 'docker tag myapp localhost:5000/myapp'. This tells Docker where to push the image. Then push the image to your private registry with 'docker push localhost:5000/myapp'. Finally, you can pull the image back from the registry using 'docker pull localhost:5000/myapp'. This process keeps your images stored locally and accessible without using public Docker Hub.

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