Rolling updates in Docker - Mini Project: Build & Apply

Rolling Updates with Docker

📖 Scenario: You manage a web application running in Docker containers. You want to update the application without downtime by using rolling updates.

🎯 Goal: Learn how to perform a rolling update of a Docker service to replace old containers with new ones smoothly.

📋 What You'll Learn

Create a Docker service running a specific image

Set a variable for the new image version

Update the Docker service to use the new image version

Verify the update by checking the service status

💡 Why This Matters

🌍 Real World

Rolling updates let you update live applications without downtime, keeping users happy.

💼 Career

DevOps engineers use rolling updates to deploy new versions safely and reliably.

1

Create a Docker service

Run the command docker service create --name webapp --replicas 3 nginx:1.21 to create a Docker service named webapp with 3 replicas using the nginx:1.21 image.

Docker

# Run the docker service create command here

Need a hint?

This command creates a service called webapp with 3 containers running nginx:1.21.

2

Set the new image version variable

Create a shell variable called NEW_IMAGE and set it to nginx:1.23.

Docker

docker service create --name webapp --replicas 3 nginx:1.21
# Set NEW_IMAGE variable to nginx:1.23

Need a hint?

Use NEW_IMAGE=nginx:1.23 to set the variable.

3

Update the Docker service with the new image

Run the command docker service update --image $NEW_IMAGE webapp to update the webapp service to use the new image stored in NEW_IMAGE.

Docker

docker service create --name webapp --replicas 3 nginx:1.21
NEW_IMAGE=nginx:1.23
# Update the webapp service to use the new image

Need a hint?

This command updates the service to the new image version smoothly.

4

Check the service update status

Run docker service ps webapp to display the status of the webapp service tasks and verify the rolling update.

Docker

docker service create --name webapp --replicas 3 nginx:1.21
NEW_IMAGE=nginx:1.23
docker service update --image $NEW_IMAGE webapp
# Check the status of the webapp service

Need a hint?

This command shows the tasks and their current state to confirm the update.