Compose
Docker Compose is a tool for defining and running multi-container applications.
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Docker Compose is a tool for defining and running multi-container applications.
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is a powerful tool that simplifies the management and orchestration of Docker applications. It allows you to define and run multi-container applications using a single , streamlining the development, deployment, and scaling of containerized environments.
Simplicity: Docker Compose abstracts away the complexity of managing multiple containers, providing a simple and intuitive way to define and run applications.
Consistency: With Docker Compose, you can define your application's configuration declaratively, ensuring consistency across different environments.
Scalability: Docker Compose enables you to scale your application effortlessly by defining and running multiple instances of your containers with a single command.
Development Environments: Docker Compose is widely used for setting up development environments, allowing developers to spin up their application stack quickly and consistently.
Testing Environments: Docker Compose facilitates the creation of isolated testing environments, enabling automated testing of multi-container applications (think GitHub Actions to build and test your application as part of it's CI/CD process).
Production Deployments: While Docker Compose is primarily used for development and testing, it can also be leveraged for deploying small-scale production environments or prototyping solutions.
The easiest and recommended way to install is to install Docker Compose as part of the Docker Desktop installation package, which provides a seamless experience for managing both Docker and Docker Compose on your local machine.
Installation Instructions:
docker compose build - Build or rebuild services.
docker compose up - Create and start containers.
docker compose down - Stop and remove containers and networks.
docker compose restart - Restart service containers.
docker compose ps - List containers.
docker compose run - Run a one-off command on a service.
docker compose exec - Execute a command in a running container.
docker compose top - Display the running processes.
Below is a sample Compose file:
docker compose run -e in the CLISet environment variables as an explicit flag on the docker compose run command.
Set environment variables from the command line environment when using docker compose up.
environment attribute in the Compose file.Set environment variables directly inside compose.yaml.
--env-file argument in the CLIenv_file attribute in the Compose fileSpecify the environment variable file from compose.yaml.
.env file placed at the root of your project directoryThe .env file should be placed at the root of the project directory next to compose.yaml.
ENV directive.Volumes in Docker Compose enable you to persist data generated by your containers across container restarts or deployments. They provide a reliable mechanism for managing and sharing data between containers.
docker compose up will automatically create volume(s) if they do not already exist.
docker compose up will mount the volume(s).
docker compose down will not remove or destroy the volume(s).
The following example shows how a volume can be connected to multiple containers simultaneously.
Running docker compose up will create the dbdata volume if it was not already created in Docker Engine. The dbdata volume would then be mounted to the backend container at /etc/data and to the backup-service container at /var/lib/backup/data.
The external attribute tells Docker Compose the volume already exists and is managed outside of the Docker Compose lifecycle. If docker compose up is run, and the volume doesn't exist, Docker Compose will return an error.
So as an example, let's imagine your app is in a directory called myapp and has the following compose.yaml:
Running docker compose up would result in:
A default network named myapp_default being created.
web and db service containers would be created and connected to the myapp_default network.
Containers could then look up services based on their names (web or db). For example, the connection string to the Postgres container would look like: postgres://db:5432.
Port mapping in Docker Compose enables you to expose container ports to the host system (HOST_PORT) or to other containers (CONTAINER_PORT) within the same Docker network. It allows external access to containerized services and facilitates communication between containers.
Docker Compose port mapping is specified by the pattern: HOST_PORT:CONTAINER_PORT
The HOST_PORT is how services outside the network can connect to the service.
The CONTAINER_PORT is how services inside the network can connect to the service.
Let's use the following Compose file as an example:
Applications or users (outside the Docker Compose network) could use the HOST_PORT connect to the service. The connection URL to the database might look like postgres://localhost:8001 if started locally.
Services (inside the Docker Compose network) would use the CONTAINER_PORT to connect to the service. The connection URL to the database would be postgres://db:5432.
test: An array of strings specifying the command for checking health.
interval: A duration of how often to run the check after the container has started.
timeout: A duration of time to consider the test a failure.
retries: Number of consecutive failures of the health check for the container to be considered unhealthy.
start_period: A duration of the allowed initialization time for the container. Failed health checks during this period will not count against the retries until after the first successful check.
start_interval: A duration of how often to run the check during the container initialization.
Dockerfiles and Docker Compose files serve complementary roles in the containerization process.
Docker Compose:
Scope: Docker Compose is primarily focused on simplifying the management of multi-container Docker applications on a single host or development environment.
Ease of Use: Docker Compose provides a simple and intuitive way to define, run, and manage multi-container applications using a single YAML file (compose.yaml).
Features: Docker Compose offers features such as service definition, container networking, volume management, and dependency management, making it well-suited for development and testing environments.
Scaling: While Docker Compose supports scaling of container instances, it is limited compared to Kubernetes and is typically used for smaller-scale deployments.
Scope: Kubernetes is a powerful container orchestration platform designed for deploying, managing, and scaling containerized applications across clusters of machines.
Complexity: Kubernetes has a steeper learning curve than Docker Compose due to its extensive feature set and complex architecture.
Scaling: Kubernetes excels at scaling containerized applications across multiple nodes in a cluster, providing features such as automatic scaling, self-healing, and rolling updates.
High Availability: Kubernetes offers built-in support for high availability and fault tolerance, with features like pod replication, load balancing, and service discovery.
Production Deployments: Kubernetes is well-suited for production deployments of containerized applications, offering advanced features for managing large-scale, mission-critical workloads.
Docker Compose is ideal for local development, testing, and small-scale deployments where simplicity and ease of use are paramount.
Kubernetes is better suited for production deployments, large-scale applications, and environments requiring high availability, scalability, and advanced orchestration features.
Ultimately, the choice between Docker Compose and Kubernetes depends on factors such as the size and complexity of your application, your deployment environment, and your organization's requirements for scalability, availability, and automation.
Docker Compose reads a (commonly named compose.yaml) that defines the configuration of your multi-container application. You then interact with your Compose application through the .
like docker compose up are used to create and manage the containers specified in the Compose file, handling tasks such as container creation, , , and service dependencies. You can then use docker compose down to stop and remove the created containers and networks.
Docker Compose provides for managing your multi-container application. Some common commands are listed below:
The Docker Compose file (compose.yaml) serves as the blueprint for your multi-container application. It defines the services, networks, volumes, and other configurations required to run your application stack. The Docker compose file follows the .
Environment variables provide a flexible way to pass configuration information to containers at runtime. Docker Compose provides 7 different ways to . They are listed below with examples in the .
Environment variables should not be used to pass sensitive information (like passwords). should be used instead.
Pass an from the command line.
Use the ENV directive in the .
Docker Engine manages and has the following behavior:
Docker Compose supports several , but an important one worth mentioning is the external attribute.
Docker Compose simplifies by automatically creating a default network for your application stack. This network allows containers to discover and communicate with each other using service names defined in the compose.yaml file. The default network name is named based on the "project name" (root directory) the compose.yaml resides.
Docker Compose supports for containers, allowing you to define conditions for determining if a container is still working. Health checks can help detect unresponsive applications even though the process is still running.
are used to define the contents and build process of individual Docker
are used to define and manage applications, orchestrating the deployment and management of multiple containers as a cohesive application stack.
While both Docker Compose and are popular tools for managing containerized applications, they serve different purposes and are designed for different use cases.