Container health checks in Docker - Mini Project: Build & Apply

Container health checks

📖 Scenario: You are managing a web application running inside a Docker container. To keep the app reliable, you want Docker to check if the app is healthy and restart it if it is not working properly.

🎯 Goal: Learn how to add a health check to a Docker container using a Dockerfile. You will create a simple web server, add a health check command, and see the health status.

📋 What You'll Learn

Create a Dockerfile with a basic web server

Add a health check command using HEALTHCHECK

Use a simple command to test the server health

Build and run the Docker container

Check the container health status

💡 Why This Matters

🌍 Real World

In real projects, health checks help keep applications running smoothly by automatically restarting containers that are not responding.

💼 Career

Knowing how to add and use container health checks is important for DevOps roles to maintain reliable and self-healing systems.

1

Create a basic Dockerfile with a web server

Create a file named Dockerfile with these exact lines to set up a simple web server using nginx image: FROM nginx:alpine

Docker

# Create a Dockerfile with FROM nginx:alpine
# Your code here

Need a hint?

This sets the base image to nginx on Alpine Linux, which is a small web server.

2

Add a health check command to the Dockerfile

Add a HEALTHCHECK instruction to the Dockerfile that runs the command curl -f http://localhost/ || exit 1 every 30 seconds with a timeout of 5 seconds. Use HEALTHCHECK --interval=30s --timeout=5s CMD curl -f http://localhost/ || exit 1.

Docker

FROM nginx:alpine
# Add HEALTHCHECK instruction below
# Your code here

Need a hint?

The health check runs curl to check if the web server responds successfully.

3

Build and run the Docker container with health check

Build the Docker image with the tag mynginx using docker build -t mynginx .. Then run the container in detached mode with the name webserver using docker run -d --name webserver mynginx.

Docker

FROM nginx:alpine
HEALTHCHECK --interval=30s --timeout=5s CMD curl -f http://localhost/ || exit 1
# Build and run commands below
# Your code here

Need a hint?

Use the exact commands to build and run the container so Docker can track health.

4

Check the container health status

Use the command docker ps to see the container status. The STATUS column should show Up (healthy) if the health check passes.

Docker

FROM nginx:alpine
HEALTHCHECK --interval=30s --timeout=5s CMD curl -f http://localhost/ || exit 1

# Build the image
# docker build -t mynginx .

# Run the container
# docker run -d --name webserver mynginx

# Check container health status
# Your code here

Need a hint?

Look for the word healthy in the status column to confirm the health check works.