Blue-green deployment with containers in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to list all running Docker containers.

Docker

docker [1]

Drag options to blanks, or click blank then click option'

Aps

Brun

Cimages

Dbuild

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'docker images' lists images, not containers.

Using 'docker run' starts a container, not lists them.

The docker ps command lists all running containers.

2fill in blank

medium

Complete the command to start a new container named 'green' from the image 'myapp:latest'.

Docker

docker run -d --name [1] myapp:latest

Drag options to blanks, or click blank then click option'

Ablue

Byellow

Cred

Dgreen

Attempts:

3 left

💡 Hint

Common Mistakes

Naming the container 'blue' which is usually the old version.

Using unrelated names like 'red' or 'yellow'.

In blue-green deployment, the new version is often called 'green'.

3fill in blank

hard

Fix the error in the command to stop the 'blue' container.

Docker

docker [1] blue

Drag options to blanks, or click blank then click option'

Astop

Bstart

Crun

Dbuild

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' which runs a container.

Using 'run' which creates a new container.

The docker stop command stops a running container.

4fill in blank

hard

Fill both blanks to create a Docker network named 'blue-green-net' and connect the 'green' container to it.

Docker

docker network [1] blue-green-net
docker network [2] blue-green-net green

Drag options to blanks, or click blank then click option'

Acreate

Bremove

Cconnect

Ddisconnect

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'remove' or 'disconnect' which delete or detach networks or containers.

Trying to connect before creating the network.

First, create the network with docker network create. Then connect the container with docker network connect.

5fill in blank

hard

Fill all three blanks to update the load balancer to point to the 'green' container, stop the 'blue' container, and remove it.

Docker

docker service update --publish-add [1] my-loadbalancer
docker [2] blue
docker [3] blue

Drag options to blanks, or click blank then click option'

A80:80

Bstop

Crm

D8080:80

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong port mappings like 8080:80 if not intended.

Removing before stopping the container.

Publish port 80 to 80 on the load balancer, stop the old 'blue' container, then remove it.

Practice

1. What is the main goal of a blue-green deployment when using containers?

easy

A. To reduce downtime by switching traffic between two identical environments

B. To increase the number of containers running simultaneously

C. To create backups of container images automatically

D. To monitor container resource usage in real-time

Solution

1. Step 1: Understand blue-green deployment concept

   Blue-green deployment uses two identical environments (blue and green) to switch traffic smoothly.

2. Step 2: Identify the main goal

   The main goal is to reduce downtime by switching user traffic from one environment to another without interruption.

3. Final Answer:

   To reduce downtime by switching traffic between two identical environments -> Option A

4. Quick Check:

   Blue-green deployment = reduce downtime [OK]

Hint: Blue-green means two environments for zero downtime [OK]

Common Mistakes:

• Confusing blue-green with scaling containers
• Thinking it creates backups automatically
• Assuming it monitors resource usage

2. Which Docker command is used to create a new container from an image for the green environment in a blue-green deployment?

easy

A. docker stop green_container

B. docker run -d --name green_container myapp:latest

C. docker push green_container myapp:latest

D. docker build -t green_container myapp/

Solution

1. Step 1: Identify command to create and start container

   The docker run command creates and starts a container from an image.

2. Step 2: Match command to green environment container creation

   docker run -d --name green_container myapp:latest runs the container detached with the name green_container.

3. Final Answer:

   docker run -d --name green_container myapp:latest -> Option B

4. Quick Check:

   Run command creates container [OK]

Hint: Use 'docker run' to start new containers [OK]

Common Mistakes:

• Using 'docker build' which builds images, not containers
• Using 'docker push' which uploads images to registry
• Using 'docker stop' which stops containers

3. Given the commands below, what will be the result after switching traffic from blue to green?

docker stop blue_container
docker start green_container

medium

A. The green environment stops, and the blue environment starts

B. Both blue and green environments run simultaneously

C. The blue environment stops, and the green environment starts serving traffic

D. No change occurs because containers are not restarted

Solution

1. Step 1: Analyze the commands

   docker stop blue_container stops the blue container. docker start green_container starts the green container.

2. Step 2: Understand traffic switch effect

   Stopping blue and starting green means traffic moves from blue to green environment.

3. Final Answer:

   The blue environment stops, and the green environment starts serving traffic -> Option C

4. Quick Check:

   Stop blue + start green = traffic switch [OK]

Hint: Stopping blue and starting green switches traffic [OK]

Common Mistakes:

• Assuming both run simultaneously after stop command
• Confusing start and stop commands
• Thinking no change happens without redeploy

4. You tried to switch traffic by running docker stop blue_container and docker start green_container, but users still reach the blue environment. What is the most likely cause?

medium

A. The load balancer or proxy is still routing traffic to the blue environment

B. The green container failed to start due to image errors

C. Docker daemon is not running on the host machine

D. The blue container was never running initially

Solution

1. Step 1: Check container states

   Stopping blue_container and starting green_container should switch environments if containers run properly.

2. Step 2: Identify traffic routing cause

   If users still reach blue, likely the load balancer or proxy still routes traffic to blue environment IP or port.

3. Final Answer:

   The load balancer or proxy is still routing traffic to the blue environment -> Option A

4. Quick Check:

   Traffic routing depends on load balancer config [OK]

Hint: Check load balancer routes after container switch [OK]

Common Mistakes:

• Assuming container start/stop alone switches traffic
• Ignoring load balancer or proxy configuration
• Thinking Docker daemon status causes routing issues

5. You want to automate blue-green deployment using Docker Compose. Which approach correctly switches traffic between blue and green services?

hard

A. Run both blue and green services with the same name and let Docker handle traffic automatically

B. Stop Docker Compose and restart it with a new image tag without changing service names

C. Build images with different tags but deploy only the blue service always

D. Use two Compose files with different service names and update the reverse proxy to point to the active service

Solution

1. Step 1: Understand Docker Compose blue-green setup

   Using two Compose files or service names (blue and green) allows running both environments side by side.

2. Step 2: Switch traffic by updating reverse proxy

   Updating the reverse proxy or load balancer to point to the active service switches traffic without downtime.

3. Final Answer:

   Use two Compose files with different service names and update the reverse proxy to point to the active service -> Option D

4. Quick Check:

   Two services + proxy update = blue-green switch [OK]

Hint: Switch proxy target between blue and green services [OK]

Common Mistakes:

• Using same service names causing conflicts
• Not updating proxy or load balancer
• Deploying only one service without switching