Module 9 - Dockerizing a Spring Boot App

Lecture: Docker and Containerization for Spring Boot Applications

1. Introduction to Containerization

Containerization is a lightweight form of virtualization that packages an application with its dependencies, configuration files, and libraries into a single, portable unit called a container. Unlike traditional virtual machines, containers share the host system’s kernel but run in isolated user spaces.

Key Benefits of Containerization:

  • Consistency: “Works on my machine” syndrome eliminated
  • Isolation: Applications run in their own environment without interference
  • Portability: Run anywhere Docker is installed (development, testing, production)
  • Scalability: Easy to scale horizontally by spinning up more containers
  • Resource Efficiency: Containers have less overhead than virtual machines

2. Docker Fundamentals

Docker is the most popular containerization platform, consisting of several key components:

Docker Components:

  • Docker Engine: The runtime that builds and runs containers
  • Docker Images: Read-only templates containing application code and dependencies
  • Docker Containers: Running instances of Docker images
  • Docker Registry: Repository for storing and distributing Docker images (e.g., Docker Hub)
  • Dockerfile: Text file with instructions to build a Docker image
  • Docker Compose: Tool for defining and running multi-container applications

Key Docker Concepts:

a) Docker Image Layers: Docker images consist of read-only layers representing filesystem differences. Each instruction in a Dockerfile creates a new layer, promoting reusability and efficient storage.

b) Container Lifecycle: Containers can be created, started, stopped, restarted, and destroyed. They’re ephemeral by design, meaning any changes to a running container are lost when the container is removed unless explicitly saved to persistent storage.

c) Docker Networking: Docker provides various network drivers (bridge, host, overlay, etc.) that enable communication between containers and with external networks.

d) Docker Volumes: Volumes provide persistent storage for containers, allowing data to survive container recreation and facilitating data sharing between containers.

3. Containerizing Spring Boot Applications

Spring Boot applications are particularly well-suited for containerization due to their self-contained nature and embedded servers.

Best Practices for Dockerizing Spring Boot Apps:

a) Building Efficient Docker Images:

  • Use multi-stage builds to reduce image size
  • Leverage optimized base images (e.g., Eclipse Temurin, Adoptium)
  • Include only necessary dependencies
  • Optimize layer caching by ordering Dockerfile instructions properly

b) Spring Boot Configuration in Containers:

  • Externalize configuration using environment variables
  • Set appropriate JVM memory settings
  • Configure application to use the correct network settings

c) Health Checks and Graceful Shutdown:

  • Implement health endpoints using Spring Boot Actuator
  • Configure proper shutdown hooks
  • Set appropriate timeouts

d) Security Considerations:

  • Run containers as non-root users
  • Remove unnecessary tools and packages
  • Scan images for vulnerabilities
  • Use read-only file systems where possible

4. Docker Compose for Multi-Container Applications

Docker Compose enables defining and running multi-container Docker applications using a YAML file to configure application services.

Docker Compose Features:

  • Define multiple services in a single file
  • Configure networking between services
  • Set up shared volumes
  • Control startup order and dependencies
  • Scale services easily

Typical Compose Setup for Spring Boot Apps:

  • Spring Boot service container
  • Database container
  • Cache container (e.g., Redis)
  • Frontend container (if applicable)

5. Container Orchestration and Kubernetes Introduction

While Docker Compose works well for development environments, production deployments benefit from container orchestration platforms like Kubernetes.

Container Orchestration Capabilities:

  • Automated deployment and scaling
  • Load balancing
  • Service discovery
  • Self-healing (automatic restarts)
  • Rolling updates
  • Resource management

Kubernetes Key Concepts:

  • Pods: Smallest deployable units containing one or more containers
  • Services: Stable network endpoints for pods
  • Deployments: Declarative updates to applications
  • ConfigMaps and Secrets: Configuration and sensitive data management
  • Namespaces: Virtual clusters within a physical cluster
  • Persistent Volumes: Storage abstraction

6. Monitoring and Logging for Containerized Applications

Containerized applications require specialized approaches to monitoring and logging.

Monitoring Strategies:

  • Expose metrics through Spring Boot Actuator
  • Collect container-level metrics (CPU, memory, network)
  • Use monitoring solutions like Prometheus and Grafana

Logging Approaches:

  • Log to standard output/error streams
  • Aggregate logs with solutions like ELK stack or Loki
  • Consider structured logging formats (JSON)

7. CI/CD for Containerized Spring Boot Applications

Modern CI/CD pipelines leverage containers for consistent build environments and artifact delivery.

Pipeline Components:

  • Source code checkout
  • Build application with tests
  • Build Docker image
  • Push to container registry
  • Deploy to staging/production

Popular CI/CD Tools:

  • GitHub Actions
  • Jenkins
  • GitLab CI/CD
  • CircleCI

Quiz: Dockerizing Spring Boot Applications

  1. What is the primary benefit of using containers for Spring Boot applications? a) Lower memory usage than running on bare metal b) Enhanced application performance c) Consistent environment across development, testing, and production d) Automatic scaling of applications

  2. In a Dockerfile, which instruction creates a new layer in the Docker image? a) FROM b) LABEL c) ENV d) All of the above

  3. Which of the following is NOT a best practice when containerizing Spring Boot applications? a) Using multi-stage builds b) Running the application as a root user c) Implementing health checks d) Externalizing configuration

  4. What is the purpose of Docker Compose? a) To build Docker images b) To define and run multi-container Docker applications c) To deploy applications to Kubernetes d) To monitor container resource usage

  5. When running a Spring Boot application in a container, which property typically needs to be set to ensure the application is accessible from outside the container? a) spring.application.name b) server.port c) server.address d) spring.profiles.active

  6. What is a Docker volume used for? a) To increase container CPU allocation b) To provide persistent storage for containers c) To improve network performance between containers d) To isolate container processes

  7. Which of the following is NOT a component of Docker? a) Docker Engine b) Docker Pod c) Docker Registry d) Docker Compose

  8. What is the recommended approach for handling logs in containerized Spring Boot applications? a) Write logs to a file inside the container b) Send logs to an external logging service via HTTP c) Log to standard output/error streams d) Disable logging to improve performance

  9. What is a multi-stage build in Docker? a) Building multiple Docker images simultaneously b) Using multiple base images in a single Dockerfile c) Using one stage to build the application and another stage for the runtime image d) Building images for multiple environments

  10. Which tool would you use to deploy and manage multiple containers across a cluster of machines? a) Docker Compose b) Kubernetes c) Maven d) Spring Boot Actuator

Quiz Answers

  1. c) Consistent environment across development, testing, and production
  2. d) All of the above
  3. b) Running the application as a root user
  4. b) To define and run multi-container Docker applications
  5. c) server.address
  6. b) To provide persistent storage for containers
  7. b) Docker Pod
  8. c) Log to standard output/error streams
  9. c) Using one stage to build the application and another stage for the runtime image
  10. b) Kubernetes

By Wahid Hamdi