Health checks in Docker in Spring Boot - Mini Project: Build & Apply

Health checks in Docker with Spring Boot

📖 Scenario: You are deploying a Spring Boot application inside a Docker container. To keep your app reliable, you want Docker to check if your app is healthy and ready to serve requests.This project will guide you to add a simple health check endpoint in your Spring Boot app and configure Docker to use it.

🎯 Goal: Build a Spring Boot app with a health check endpoint at /actuator/health and configure a Dockerfile with a HEALTHCHECK instruction that uses this endpoint.

📋 What You'll Learn

Create a Spring Boot application with the Actuator dependency

Enable the health endpoint at /actuator/health

Write a Dockerfile that builds the Spring Boot app image

Add a Docker HEALTHCHECK instruction that queries http://localhost:8080/actuator/health

💡 Why This Matters

🌍 Real World

Health checks help Docker and orchestration tools know if your app is running well and ready to serve users. This avoids downtime and improves reliability.

💼 Career

Understanding health checks is important for DevOps, backend development, and cloud deployment roles where containerized apps are common.

1

Add Actuator dependency and enable health endpoint

In your Spring Boot build.gradle or pom.xml, add the Actuator dependency. Then, in src/main/resources/application.properties, enable the health endpoint by adding management.endpoints.web.exposure.include=health.

Spring Boot

# Add Actuator dependency and enable health endpoint
# Your code here

Need a hint?

The Actuator dependency provides the health endpoint. You must expose it explicitly in application.properties.

2

Create a Dockerfile to build the Spring Boot app image

Create a Dockerfile that uses openjdk:17-jdk-slim as the base image. Copy the built jar file named app.jar into the container and set the command to run it with java -jar /app.jar.

Spring Boot

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-actuator'
}

# In src/main/resources/application.properties
management.endpoints.web.exposure.include=health

# Create Dockerfile below
# Your code here

Need a hint?

Use the official OpenJDK 17 slim image. Copy your jar to /app.jar and run it with java -jar.

3

Add a Docker HEALTHCHECK instruction

In the Dockerfile, add a HEALTHCHECK instruction that runs curl -f http://localhost:8080/actuator/health || exit 1 every 30 seconds with a timeout of 5 seconds.

Spring Boot

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-actuator'
}

# In src/main/resources/application.properties
management.endpoints.web.exposure.include=health

# Dockerfile
FROM openjdk:17-jdk-slim
COPY build/libs/app.jar /app.jar
CMD ["java", "-jar", "/app.jar"]

# Add HEALTHCHECK instruction below
# Your code here

Need a hint?

The HEALTHCHECK runs curl to check the health endpoint. If curl fails, it exits with 1 to mark unhealthy.

4

Complete the Dockerfile with exposed port

In the Dockerfile, add an EXPOSE 8080 instruction so Docker knows the app listens on port 8080.

Spring Boot

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-actuator'
}

# In src/main/resources/application.properties
management.endpoints.web.exposure.include=health

# Dockerfile
FROM openjdk:17-jdk-slim
COPY build/libs/app.jar /app.jar
CMD ["java", "-jar", "/app.jar"]

HEALTHCHECK --interval=30s --timeout=5s CMD curl -f http://localhost:8080/actuator/health || exit 1

# Add EXPOSE 8080 below
# Your code here

Need a hint?

Expose port 8080 so Docker knows which port the app uses.