Pushing and pulling images in GCP - Commands & Configuration

Introduction

When you build software that runs in containers, you need a place to store those container images so you can use them later or share them. Pushing means sending your container image to a storage place called a registry. Pulling means getting that image back from the registry to run it on a computer.

When you want to save your container image to Google Container Registry so others can use it.

When you need to run your container on a Google Cloud server and must download the image first.

When you update your app and want to upload the new version of the container image.

When you want to share your container image with your team using Google Cloud.

When you want to move your container image between different computers or environments.

Commands

This command sets up your computer to securely talk to Google Container Registry by configuring Docker with your Google Cloud login.

Terminal

gcloud auth configure-docker

Expected Output

Docker configuration file updated.

Credentials helper configured for gcr.io, us.gcr.io, eu.gcr.io, asia.gcr.io

This builds a container image from your current folder and tags it with the Google Container Registry path and version v1.

Terminal

docker build -t gcr.io/my-project/my-app:v1 .

Expected Output

Sending build context to Docker daemon  8.192kB

Step 1/5 : FROM python:3.9-slim

 ---> 123abc456def

Step 2/5 : COPY . /app

 ---> Using cache

Step 3/5 : WORKDIR /app

 ---> Using cache

Step 4/5 : RUN pip install -r requirements.txt

 ---> Using cache

Step 5/5 : CMD ["python", "app.py"]

 ---> Using cache

Successfully built abcdef123456

Successfully tagged gcr.io/my-project/my-app:v1

→

-t - Tags the image with a name and version

This uploads your tagged container image to Google Container Registry so it can be stored and shared.

Terminal

docker push gcr.io/my-project/my-app:v1

Expected Output

The push refers to repository [gcr.io/my-project/my-app]

abcdef123456: Pushed

v1: digest: sha256:abcdef1234567890 size: 1234

This downloads the container image tagged v1 from Google Container Registry to your local computer so you can run it.

Terminal

docker pull gcr.io/my-project/my-app:v1

Expected Output

v1: Pulling from my-project/my-app

Digest: sha256:abcdef1234567890

Status: Downloaded newer image for gcr.io/my-project/my-app:v1

gcr.io/my-project/my-app:v1

Key Concept

If you remember nothing else from this pattern, remember: pushing sends your container image to the cloud registry, and pulling gets it back to run anywhere.

Common Mistakes

Trying to push an image without tagging it with the full registry path.

Docker does not know where to send the image without the full registry address, so push fails.

Always tag your image with the full Google Container Registry path like gcr.io/project-id/image-name:tag before pushing.

Not running 'gcloud auth configure-docker' before pushing or pulling.

Docker cannot authenticate with Google Container Registry, so push or pull commands fail with permission errors.

Run 'gcloud auth configure-docker' once to set up authentication for Docker.

Summary

Run 'gcloud auth configure-docker' to let Docker talk to Google Container Registry.

Build your container image and tag it with the full registry path.

Push the tagged image to Google Container Registry to store it.

Pull the image from the registry to download and run it anywhere.

Practice

1. What does the docker push command do in Google Cloud Platform?

easy

A. Downloads a container image from Google Container Registry

B. Uploads your container image to Google Container Registry

C. Deletes a container image from your local machine

D. Builds a new container image from a Dockerfile

Solution

1. Step 1: Understand the purpose of docker push

   The docker push command uploads your local container image to a remote registry like Google Container Registry.

2. Step 2: Differentiate from other commands

   docker pull downloads images, docker build creates images, and deleting is a separate action.

3. Final Answer:

   Uploads your container image to Google Container Registry -> Option B

4. Quick Check:

   Push = Upload image to registry [OK]

Hint: Push means upload image to cloud registry [OK]

Common Mistakes:

• Confusing push with pull
• Thinking push builds the image
• Assuming push deletes images

2. Which of the following is the correct syntax to tag a local Docker image named myapp with the Google Container Registry path gcr.io/my-project/myapp:v1?

easy

A. docker tag myapp gcr.io/my-project/myapp:v1

B. docker push myapp gcr.io/my-project/myapp:v1

C. docker pull myapp gcr.io/my-project/myapp:v1

D. docker build myapp gcr.io/my-project/myapp:v1

Solution

1. Step 1: Identify the tagging command

   The docker tag command assigns a new name (including registry path) to an existing local image.

2. Step 2: Confirm correct syntax

   The syntax is docker tag SOURCE_IMAGE TARGET_IMAGE, so docker tag myapp gcr.io/my-project/myapp:v1 is correct.

3. Final Answer:

   docker tag myapp gcr.io/my-project/myapp:v1 -> Option A

4. Quick Check:

   Tag syntax = docker tag SOURCE TARGET [OK]

Hint: Tag uses 'docker tag source target' syntax [OK]

Common Mistakes:

• Using push or pull instead of tag
• Reversing source and target images
• Confusing build with tag

3. Given the commands below, what will be the result of running docker images?

docker tag myapp gcr.io/my-project/myapp:v2
docker push gcr.io/my-project/myapp:v2

medium

A. The local image list will only show myapp without the tag

B. The local image list will be empty

C. The local image list will include gcr.io/my-project/myapp:v2

D. The local image list will show myapp:v2 but not the full registry path

Solution

1. Step 1: Understand tagging effect on local images

   Tagging creates a new name for the same local image, so gcr.io/my-project/myapp:v2 appears locally.

2. Step 2: Recognize push does not remove local images

   Pushing uploads the image but does not delete local copies, so the tagged image remains listed.

3. Final Answer:

   The local image list will include gcr.io/my-project/myapp:v2 -> Option C

4. Quick Check:

   Tag adds local name; push uploads but keeps local image [OK]

Hint: Tag adds local name; push uploads but keeps local image [OK]

Common Mistakes:

• Thinking push deletes local images
• Assuming tag does not create new local name
• Confusing image names without registry path

4. You tried to push an image with the command docker push myapp:v1 but got an error saying the repository was not found. What is the most likely cause?

medium

A. You forgot to tag the image with the full registry path before pushing

B. You need to run docker pull before pushing

C. The image name myapp:v1 is invalid syntax

D. You must delete the local image before pushing

Solution

1. Step 1: Understand push requires full registry path

   To push to Google Container Registry, the image must be tagged with the full path like gcr.io/project-id/image:tag.

2. Step 2: Identify missing tag as cause of error

   Using only myapp:v1 lacks registry info, so the push command cannot find the remote repository.

3. Final Answer:

   You forgot to tag the image with the full registry path before pushing -> Option A

4. Quick Check:

   Push needs full registry tag [OK]

Hint: Push needs full registry path tag [OK]

Common Mistakes:

• Trying to pull before push
• Assuming image name syntax is wrong
• Deleting local image before push

5. You want to update your app image in Google Container Registry with a new version. Which sequence of commands correctly tags, pushes, and then pulls the updated image for deployment?

hard

A. docker build myapp:v2 && docker pull gcr.io/my-project/myapp:v2 && docker push gcr.io/my-project/myapp:v2

B. docker pull gcr.io/my-project/myapp:v2 && docker tag myapp:v2 && docker push myapp:v2

C. docker push myapp:v2 && docker tag myapp gcr.io/my-project/myapp:v2 && docker pull myapp:v2

D. docker tag myapp gcr.io/my-project/myapp:v2 && docker push gcr.io/my-project/myapp:v2 && docker pull gcr.io/my-project/myapp:v2

Solution

1. Step 1: Tag the local image with the full registry path

   Use docker tag myapp gcr.io/my-project/myapp:v2 to prepare the image for pushing.

2. Step 2: Push the tagged image to Google Container Registry

   Run docker push gcr.io/my-project/myapp:v2 to upload the image.

3. Step 3: Pull the updated image to confirm availability for deployment

   Use docker pull gcr.io/my-project/myapp:v2 to download the image where needed.

4. Final Answer:

   docker tag myapp gcr.io/my-project/myapp:v2 && docker push gcr.io/my-project/myapp:v2 && docker pull gcr.io/my-project/myapp:v2 -> Option D

5. Quick Check:

   Tag, push, then pull sequence [OK]

Hint: Tag with full path, push, then pull updated image [OK]

Common Mistakes:

• Pushing before tagging with full path
• Pulling before pushing updated image
• Incorrect command order