ACR image building and pushing in Azure - Commands & Configuration

Introduction

Building and pushing container images to Azure Container Registry (ACR) lets you store your app images securely in the cloud. This helps you share and deploy your app easily without managing local storage.

When you want to save your app's container image in a private cloud registry for secure access.

When you need to share your container image with your team or deployment pipelines.

When you want to automate building and pushing images as part of your development workflow.

When you want to keep your container images close to your Azure cloud resources for faster deployments.

When you want to avoid managing your own container registry infrastructure.

Config File - Dockerfile

Dockerfile

FROM nginx:1.23.3-alpine
COPY ./html /usr/share/nginx/html
EXPOSE 80

This Dockerfile uses a small Nginx image as the base.

It copies your website files from the local 'html' folder into the container.

It exposes port 80 so the web server can receive traffic.

Commands

This command logs you into your Azure Container Registry named 'exampleRegistry' so you can push and pull images securely.

Terminal

az acr login --name exampleRegistry

Expected Output

Login Succeeded

→

--name - Specifies the name of your Azure Container Registry.

This builds your Docker image from the Dockerfile in the current folder and tags it with your registry URL and version 'v1'.

Terminal

docker build -t exampleRegistry.azurecr.io/my-app:v1 .

Expected Output

Sending build context to Docker daemon  3.07kB

Step 1/3 : FROM nginx:1.23.3-alpine

 ---> 3f9f1b8f1a1a

Step 2/3 : COPY ./html /usr/share/nginx/html

 ---> Using cache

 ---> 7a8b9c0d1e2f

Step 3/3 : EXPOSE 80

 ---> Running in 4c5d6e7f8g9h

Removing intermediate container 4c5d6e7f8g9h

 ---> 1a2b3c4d5e6f

Successfully built 1a2b3c4d5e6f

Successfully tagged exampleRegistry.azurecr.io/my-app:v1

→

-t - Tags the image with the full registry path and version.

This pushes your tagged image to your Azure Container Registry so it can be used by your deployments.

Terminal

docker push exampleRegistry.azurecr.io/my-app:v1

Expected Output

The push refers to repository [exampleRegistry.azurecr.io/my-app]

1a2b3c4d5e6f: Pushed 

v1: digest: sha256:abcdef1234567890 size: 1234

This command lists all the image tags available in the 'my-app' repository in your Azure Container Registry to verify your push.

Terminal

az acr repository show-tags --name exampleRegistry --repository my-app

Expected Output

[

  "v1"

]

→

--name - Specifies the Azure Container Registry name.

→

--repository - Specifies the repository name inside the registry.

Key Concept

If you remember nothing else from this pattern, remember: you must tag your image with your registry's full login server name before pushing it to Azure Container Registry.

Common Mistakes

Trying to push an image without logging into ACR first.

Docker cannot authenticate to your private registry, so the push fails.

Always run 'az acr login --name yourRegistry' before pushing images.

Tagging the image without the full registry login server URL.

Docker pushes to Docker Hub by default, not your Azure registry.

Tag images as 'yourRegistry.azurecr.io/imageName:tag' to push to ACR.

Not verifying the image push by listing tags in the registry.

You might think the push succeeded but the image is not available for deployment.

Use 'az acr repository show-tags' to confirm your image is in the registry.

Summary

Log in to your Azure Container Registry to authenticate your Docker client.

Build your Docker image and tag it with your registry's full login server name.

Push the tagged image to your Azure Container Registry.

Verify the image is stored by listing the repository tags in your registry.

Practice

1. What is the primary purpose of the az acr build command in Azure Container Registry (ACR)?

easy

A. To run a container instance in Azure

B. To delete an image from ACR

C. To create a new Azure Container Registry

D. To build a container image and push it directly to ACR

Solution

1. Step 1: Understand the command purpose

   The az acr build command is designed to build container images from a Dockerfile and push them to an Azure Container Registry.

2. Step 2: Compare options with command function

   Options A, B, and C describe other unrelated actions like deleting images, creating registries, or running containers, which are not the purpose of az acr build.

3. Final Answer:

   To build a container image and push it directly to ACR -> Option D

4. Quick Check:

   az acr build = build and push image [OK]

Hint: Remember: az acr build builds and pushes images [OK]

Common Mistakes:

• Confusing build with delete or create registry commands
• Thinking az acr build runs containers
• Assuming it only builds locally without pushing

2. Which of the following is the correct syntax to build and push an image named myapp:v1 to an Azure Container Registry named myregistry using az acr build?

easy

A. az acr build --registry myregistry --image myapp:v1 .

B. az acr build --image myapp:v1 --registry myregistry

C. az acr build --name myregistry --tag myapp:v1 .

D. az acr build --push --image myapp:v1 --registry myregistry

Solution

1. Step 1: Identify correct parameter order and names

   The correct syntax uses --registry to specify the registry, --image for image name and tag, followed by the build context path (here . for current directory).

2. Step 2: Validate options

   az acr build --image myapp:v1 --registry myregistry omits the required build context path (.). az acr build --registry myregistry --image myapp:v1 . matches the correct syntax. az acr build --name myregistry --tag myapp:v1 . uses incorrect flags --name and --tag which are invalid. az acr build --push --image myapp:v1 --registry myregistry uses --push which is not a valid flag for az acr build.

3. Final Answer:

   az acr build --registry myregistry --image myapp:v1 . -> Option A

4. Quick Check:

   Correct flags: --registry, --image, context path [OK]

Hint: Use --registry then --image followed by context path [OK]

Common Mistakes:

• Using --name instead of --registry
• Adding unsupported flags like --push
• Omitting the build context path

3. Given the command:

az acr build --registry myregistry --image sampleapp:latest ./app

What will happen after this command runs successfully?

medium

A. The image sampleapp:latest is pulled from myregistry and run locally

B. The Dockerfile in ./app is built into an image tagged sampleapp:latest and pushed to myregistry

C. A new Azure Container Registry named sampleapp is created

D. The local Docker daemon builds the image but does not push it

Solution

1. Step 1: Understand the command behavior

   The az acr build command builds the Dockerfile found in the specified path (./app) and pushes the resulting image to the specified Azure Container Registry (myregistry) with the given tag (sampleapp:latest).

2. Step 2: Eliminate incorrect options

   The image sampleapp:latest is pulled from myregistry and run locally describes pulling and running, which az acr build does not do. A new Azure Container Registry named sampleapp is created talks about creating a registry, which requires a different command. The local Docker daemon builds the image but does not push it suggests local build only, but az acr build builds in Azure and pushes automatically.

3. Final Answer:

   The Dockerfile in ./app is built into an image tagged sampleapp:latest and pushed to myregistry -> Option B

4. Quick Check:

   az acr build builds and pushes image [OK]

Hint: az acr build builds remotely and pushes automatically [OK]

Common Mistakes:

• Thinking image is only built locally
• Confusing build with run or pull
• Assuming registry is created automatically

4. You run the command:

az acr build --registry myregistry --image myapp:v2 ./src

but get an error saying Dockerfile not found. What is the most likely cause?

medium

A. The image tag myapp:v2 is invalid

B. The registry name myregistry is incorrect

C. The ./src directory does not contain a Dockerfile

D. You forgot to login to Azure CLI

Solution

1. Step 1: Analyze the error message

   The error Dockerfile not found means the build context directory (./src) does not have a Dockerfile, which is required to build the image.

2. Step 2: Check other options

   Incorrect registry or image tag would cause different errors. Forgetting to login would cause authentication errors, not missing Dockerfile.

3. Final Answer:

   The ./src directory does not contain a Dockerfile -> Option C

4. Quick Check:

   Missing Dockerfile = Dockerfile not found error [OK]

Hint: Ensure Dockerfile exists in build context folder [OK]

Common Mistakes:

• Assuming registry or tag causes Dockerfile error
• Ignoring the build context path
• Not verifying Dockerfile presence before build

5. You want to build and push multiple images with tags v1 and latest for your app using az acr build. Which approach correctly achieves this in a single command?

hard

A. Use --image myapp:v1 --image myapp:latest with the build context path

B. Run az acr build twice, once for each tag

C. Use --tag v1,latest with the image name

D. Build locally twice and push manually

Solution

1. Step 1: Understand multi-tag build syntax

   The az acr build command supports specifying multiple --image flags to tag the same build with different tags in one command.

2. Step 2: Evaluate options

   Use --image myapp:v1 --image myapp:latest with the build context path correctly uses multiple --image flags. Run az acr build twice, once for each tag works but is two commands, not single. Use --tag v1,latest with the image name uses an invalid --tag flag. Build locally twice and push manually is manual and not a single command.

3. Final Answer:

   Use --image myapp:v1 --image myapp:latest with the build context path -> Option A

4. Quick Check:

   Multiple --image flags tag multiple images [OK]

Hint: Use multiple --image flags to tag in one build [OK]

Common Mistakes:

• Trying to use --tag with multiple tags
• Running separate builds unnecessarily
• Building locally instead of using az acr build