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Welcome to Day 18 of the #90DaysOfDevOps challenge. Today, we will explore an exciting Docker project specifically designed for DevOps Engineers. Our focus will be on Docker Compose, a powerful tool that simplifies the management of multi-container applications. By leveraging Docker Compose, we can easily orchestrate and deploy complex application stacks. Let's get started.
Docker Compose is a command-line tool that allows us to define and manage multi-container applications. With Docker Compose, we can describe our application's services, networks, and volumes using a simple YAML file. It provides a declarative approach to defining the infrastructure requirements of our application, making it easier to manage and reproduce our environment across different stages of development, testing, and production.
Install Docker Compose
To begin, we need to ensure that Docker Compose is installed on our system. Here are the steps to install Docker Compose on Ubuntu:
Update the package index, and install the latest version of Docker Compose:
sudo apt-get update sudo apt-get install docker-compose-plugin
Verify that Docker Compose is installed correctly by checking the version:
docker compose version
If the installation was successful, you should see the version information for Docker Compose.
Docker Compose CLI Reference
The docker-compose command provides a number of subcommands to manage Docker containers with docker-compose. Please find below details of the subcommands. Before reading the below commands, remember that you passed the service name as an argument (not the container name)
The build option is used to build images for services for which build is defined.
$ docker-compose build ## Build all services $ docker-compose build web ## Build single service
Use to create docker containers with available services in
docker-compose.yml file in the current directory. Use
-d switch to launch containers in daemon mode.
$ docker-compose up -d ## Create all containers $ docker-compose up -d web ## Create single container
This will stop and delete all containers, network and associated images for the services defined in a config file
$ docker-compose down ## Restart all containers $ docker-compose down web ## Restart single container
This will list all containers created for the services defined in a config file with their status, port bindings and command.
$ docker-compose ps
This will execute a command to the running container. For example, list files in a container associated with a web service.
$ docker-compose exec web ls -l
This will start stopped containers of the services defined in the config file
$ docker-compose start ## Start all containers $ docker-compose start web ## Start single container
This will stop running containers for the services defined in the config file
$ docker-compose stop ## Stop all containers $ docker-compose stop web ## Stop single container
This will restart containers of the services defined in the config file
$ docker-compose restart ## Restart all containers $ docker-compose restart web ## Restart single container
This will pause running containers for the services defined in the config file.
$ docker-compose pause ## Pause all containers $ docker-compose pause web ## Pause single container
This will start paused containers for the services defined in the config file.
$ docker-compose pause ## Start all paused containers $ docker-compose pause web ## Start single paused container
This will remove stopped containers for the services defined in the config file.
$ docker-compose rm ## Start all paused containers $ docker-compose pause web ## Start single paused container
How to Run Docker Commands Without Sudo?
By default, running Docker commands requires sudo or root privileges. However, it is possible to grant our user permission to run Docker commands without sudo. Here's how you can achieve this:
Add the user to the
dockergroup by running the following command (replace
<username>with your actual username):
sudo usermod -aG docker <username>
After adding the user to the
dockergroup, it is necessary to reboot the system for the changes to take effect. Restart your machine by running:
After rebooting, you should be able to run Docker commands without sudo.
What is YAML?
YAML, which stands for "YAML Ain't Markup Language" is a popular data serialization format widely used in the DevOps field for creating configuration files. It provides a human-readable and machine-friendly syntax that allows developers and system administrators to define structured data clearly and concisely.
One of the primary use cases of YAML in DevOps is for configuring and defining application settings and environments. For example, in Docker Compose, a YAML file is used to specify the services, networks, volumes, and other configurations required to run a multi-container application.
YAML files utilize indentation and simple syntax to represent data hierarchically, making it easy to understand and work with. This readability is one of YAML's key strengths, as it enables both humans and machines to parse and interpret the data effortlessly.
Additionally, YAML supports various data types such as scalars (strings, numbers, booleans), sequences (arrays, lists), and mappings (key-value pairs). This flexibility allows for the representation of complex configurations and relationships between different components of an application.
Learn how to use the docker-compose.yml file, to set up the environment, configure the services and links between different containers, and also to use environment variables in the docker-compose.yml file
Let's go through the
docker-compose.yml file and understand how it sets up the environment, configures services, establishes links between containers, and uses environment variables:
version : "3.3" services: web: image: nginx:latest ports: - "80:80" db: image: mysql ports: - "3306:3306" environment: - "MYSQL_ROOT_PASSWORD=test@123"
version: "3.3"line specifies the version of the Docker Compose file syntax being used.
servicessection, two services are defined:
db. Each service represents a container.
webservice uses the
nginx:latestimage, which is a popular web server. It is accessible through port mapping defined as
ports: - "80:80", where port 80 of the container is mapped to port 80 of the host machine. This allows accessing the web server running inside the container via
http://localhoston the host machine.
dbservice uses the
mysqlimage, which is a widely used relational database management system. Similar to the
webservice, it also has port mapping defined as
ports: - "3306:3306", allowing access to the MySQL database server running inside the container via
localhoston port 3306 of the host machine.
dbservice sets the
MYSQL_ROOT_PASSWORDenvironment variable to
test@123. This sets the root password for the MySQL database inside the container to ensure secure access.
By running the
docker-compose up command in the directory where the
docker-compose.yml file is located, Docker Compose will create and start the defined services. It automatically manages the networking between containers and sets up the specified environment variables.
Pull a pre-existing Docker image from a public repository (e.g. Docker Hub) and run it on your local machine. Run the container as a non-root user. Make sure you reboot the instance after giving permission to the user.
Use the docker pull command followed by the image name and tag to pull the image.
docker pull nginx:latest
Inspect the container's running processes and exposed ports using the docker inspect command.
docker inspect <container-id>
Use the docker logs command to view the container's log output.
docker logs <container-id>
Use the docker stop and docker start commands to stop and start the container.
docker stop command followed by the container ID or name to stop the running container. For example:
docker stop <container-id>
docker start command followed by the container ID or name to start the stopped container. For example:
docker start <container-id>
Use the docker rm command to remove the container when you're done.
docker rm <container-id>
Running my own docker-compose file to create Jenkins and Portainer containers
version: "3.9" services: portainer: container_name: portainer image: portainer/portainer-ce:latest restart: always volumes: - /var/run/docker.sock:/var/run/docker.sock - portainer_data:/data ports: - 9000:9000 jenkins: container_name: jenkins image: jenkins/jenkins:lts restart: always volumes: - jenkins_data:/var/jenkins_home ports: - 8081:8080 - 50000:50000 volumes: portainer_data: jenkins_data:
versionfield specifies the version of the Docker Compose file format being used (in this case, version 3.9).
servicessection, we define two services:
imagefield specifies the Portainer image to be used.
volumesfield mounts the Docker socket and a volume for Portainer data persistence.
portsfield maps port 9000 of the container to port 9000 of the host machine.
imagefield specifies the Jenkins image to be used.
volumesfield mounts a volume for Jenkins data persistence.
portsfield maps ports 8081 and, 50000 of the container to the same ports on the host machine.
This example sets up Portainer for managing Docker containers and Jenkins for continuous integration and continuous delivery (CI/CD) processes. You can access Portainer on port 9000 of the host machine and Jenkins on port 8081.
Congratulations on completing Day 18 of the #90DaysOfDevOps challenge. Today, we delved into Docker Compose and explored its features for orchestrating multi-container applications. We learned how to define services, configure dependencies, and utilize environment variables using a docker-compose.yml file. Additionally, we discovered essential Docker Compose CLI commands and discussed how to run Docker commands without sudo.
Get ready for Day 19, where we will continue exploring Docker for DevOps Engineers. Stay tuned!
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