How to Build and run your app with Compose

Docker Compose tool is used to define and start running multi-container Docker applications. Configuration is as easy, there would be a YAML file to configure your application’s services/networks/volumes, etc., Then, with a single command, you can create and start all the services from the compose configuration.

Here are the key steps :

1. Define Dockerfile for your app’s environment.
2. Define docker-compose.yml for the services that make up your app services.
3. Run docker-compose up and Compose starts and runs your entire app.

This quickstart assumes basic understanding of Docker concepts, please refer earlier posts for understanding on Docker & how to install and containerize applications.In this post,we can look at how to use existing Docker compose file and define services.

Key Features of Docker Compose

• When you define Compose file,you can use project name to isolate environments from each other. This could be useful in cases like creating multiple copies of a single environment or segregate the builds by unique build number.
• Compose caches the configuration used to create a container. When you restart a service that has not changed, Compose re-uses the existing containers.It means that you can make changes to your environment very quickly.
• Compose preserves all volumes used by your services. When docker-compose up runs, if it finds any containers from previous runs, it copies the volumes from the old container to the new container. This process ensures that any data you’ve created in volumes isn’t lost.
• Compose supports variables in the Compose file. You can use these variables to customize your composition for different environments, or different users.

In the next section,we can look at how define services in compose file for sample application with Angular as front end,Spring Boot as API and  Postgres as Database.

#1.Definition of Docker files

We have already defined below docker files in the previous posts here,here & here. Create new project directory and copy all dockerfiles to this folder.

Angular Application Docker file

FROM httpd:2.4
#copy angular dist folder to container 
COPY dist/ /usr/local/apache2/htdocs/

#copy htaccess and httpd.conf to container
COPY .htaccess /usr/local/apache2/htdocs/
COPY httpd.conf /usr/local/apache2/conf/httpd.conf

#change permissions
RUN chmod -R 755 /usr/local/apache2/htdocs/

#expose port
EXPOSE 4200

Spring Boot API Docker file

FROM openjdk:8-jre
WORKDIR /
#add required jars
ADD spring-boot-rest-postgresql-0.0.1-SNAPSHOT.jar spring-boot-rest-postgresql-0.0.1-SNAPSHOT.jar

#expose port
EXPOSE 8080
#cmd to execute
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/spring-boot-rest-postgresql-0.0.1-SNAPSHOT.jar"]

Database Docker file

FROM postgres:9.5
#init.sql to create database
COPY init.sql /docker-entrypoint-initdb.d/

# Adjust PostgreSQL configuration to accept remote connections 
RUN echo "host all all 0.0.0.0/0 md5" >> /var/lib/postgresql/data/pg_hba.conf

RUN echo "listen_addresses='*'" >> /var/lib/postgresql/data/postgresql.conf

# expose port
EXPOSE 5432

Now that we have dockerfiles ready for all of the application,next step is to define compose file.

#2.Define services in Docker compose file

Create a file called docker-compose.yml in your project directory and paste the following:

version: '3'
services:
   ui:
    build:
      context: .
      dockerfile: UIDockerfile
    ports:
      - '4200:4200'
    networks:
      - samplenet
    links:
      - 'api:api'
  api:
   build:
     context: .
     dockerfile: AppDockerfile
   ports:
     - '8080:8080'
   depends_on:
    - db
    - rabbitmq
   networks:
    - samplenet
   links:
    - 'db:db'
  db: 
   build:
    context: .
    dockerfile: DBDockerfile
  volumes:
   - 'postgresdb:/var/lib/postgresql/data'
  environment:
   POSTGRES_USER: postgres
   POSTGRES_PASSWORD: postgres
   POSTGRES_DB: testdb
  ports:
   - '5432:5432'
  healthcheck:
   test:
     - CMD-SHELL
     - 'pg_isready -U postgres'
   interval: 10s
   timeout: 5s
   retries: 5
  networks:
   - samplenet
 rabbitmq:
  image: 'rabbitmq:3.5.3-management'
  container_name: rabbitmq2
  ports:
   - '5672:5672'
   - '15672:15672'
  networks:
   - samplenet
networks:
samplenet: null
volumes:
postgresdb: {}

Above compose file defines 4 services as below:

• ui : this is for angular application,it uses an image that’s built from the UIDockerfile in the current directory and forwards the exposed port 4200 on the container to port 4200 on the host machine.
• api : this is for spring boot application,it uses an image that’s built from the AppDockerfile in the current directory and forwards the exposed port 8080 on the container to port 8080 on the host machine. Note this is dependent on db and rabbitmq services.
• db : this is for postgresdb application,it uses an image that’s built from the DBDockerfile in the current directory and forwards the exposed port 5432 on the container to port 5432 on the host machine.
• rabbitmq : Uses rabbitmq:3.5.3-management public image from Dockerhub registry and uses ports 5672,15672
• All the above services uses samplenet network and
• Persistent volume postgresdb definition is for db service
• Added healthcheck section for db service to keep tab on the health of the database
• depends_on denotes the service dependencies. When you start the services, compose would start the dependent services as well.

#3.Build and run your app with Compose

In the current project directory, run docker-compose up to start the application. Compose pulls all the required Docker image, builds an image for your code, and starts the services you defined.

You can stop the application, either by running docker-compose down from within your project directory or by hitting CTRL+C in the original terminal where you started the app.

To apply patches/updates to any of application container(s) they can be stopped using below command

docker-compose stop <service name>

or if you want to force stop then use below command

docker-compose kill <service name>

To bring up service back online, use below command

docker-compose start <service name>

If you don’t want to compile dependencies, use below command

docker-compose up -d --no-deps <service name>

--no-deps will not start linked services

-d Detached mode

If there are existing containers for a service, and the service’s configuration or image was changed after the container’s creation, docker-compose up command picks up the changes by stopping and recreating the containers.

Congrats! today we have learnt how to build and run your application using Docker compose utility.

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Useful Resources:

• Official documentation as a reference to understand any command.
• Docker build reference
• Docker run reference
• Best Practices article on writing Docker files.
• Test your knowledge on Dockerfile.
• Full list of Compose commands
• Compose configuration file reference
• Monitoring Docker containers using Prometheus + cAdvisor + Grafana
• How to aggregate Docker Container logs and analyse with ELK stack ?
• Implementing secure containers using gVisor+Docker tutorial