Docker has become an indispensable tool in the software development and deployment pipeline for developers and DevOps employees. It packs applications into small, lightweight containers, simplifying creating, sharing, and using them. However, Dockerfile and Docker Compose are two technologies frequently mentioned in discussions about building and managing Docker containers. Understanding their distinctions is essential to comprehensive DevOps Training, as they have different functions and are employed in various contexts.
In this blog, you will learn the distinctions between Dockerfile vs Docker Compose, when to use each, and how to combine them to optimise your containerisation workflow.
Table of Contents
- What is a Dockerfile?
- What is Docker Compose?
- Key Differences Between Dockerfile and Docker Compose
- When to Use Dockerfile vs Docker Compose
- How Dockerfile and Docker Compose Work Together
- Conclusion
What is a Dockerfile?
It is a script that contains the instructions required to build a Docker image. Consider it your application’s blueprint. The Dockerfile contains all the commands a user could use to assemble an image from the command line. By writing a Dockerfile, you can automate making unique Docker images with your application, dependencies, configurations, and environment variables.
Here’s a simple example of a Dockerfile:
The base image (python:3.8-slim-buster) is the first thing we load into this Dockerfile. Next, we set up a working directory, copy the application files, install the dependencies, expose a port, establish an environment variable, and provide the command to launch the application. Every line in the Dockerfile denotes a stage in creating an image.
What is Docker Compose?
Docker Compose defines and executes multi-container applications, whereas a Dockerfile is mainly used to construct single images. The application’s services, networks, and volumes are configured via a YAML file. Multiple Docker containers can be managed and operated concurrently with Docker Compose, an advantageous feature for microservices architectures or applications comprising numerous interconnected services.
Here’s an example of a docker compose.yml file:
In this example, the web and Redis services are defined in the docker-compose.yml file. The web service mounts a volume, exposes port 5000, is constructed using the Dockerfile in the current directory, and depends on the Redis service. The Redis service uses the official Redis image. Both services can be launched with a single command (docker-compose up) and connected automatically according to the Compose file’s definition.
Key Differences Between Dockerfile and Docker Compose
Purpose and Functionality:
- A Docker image is created using a Dockerfile. It includes building instructions for a single container.
- Conversely, multi-container Docker applications are defined and managed using Docker Compose. It describes the networks, shared volumes, and cooperative mechanisms among numerous services.
Usage:
- When you need to create a unique Docker image for your application, you use a Dockerfile. It lets you specify your application’s requirements and the environment in which it operates.
- When you must have numerous containers communicate with one another, you utilise Docker Compose. With its assistance, you can easily start, pause, and control every service with a single command by orchestrating these containers.
Syntax and Structure:
- A script file with commands written in a particular syntax that Docker recognises is called a Dockerfile. A layer is created in the Dockerfile for every instruction in the Docker image.
- A docker-compose.yml file specifies the volumes, networks, and services needed for a multi-container application using YAML syntax. Commands are less important than settings.
Single vs Multi-Container Focus:
- The environment setup and configuration of a single application container is the focus of a Dockerfile.
- Docker Compose handles the setup, linking, and administration of several containers that comprise an entire application stack.
Dependency Management:
- A Dockerfile does not handle multiple container dependencies. Its sole focus is on creating an image of a single container.
- You can define dependencies between services with Docker Compose. For instance, to ensure that one container starts before another, you can set a depends_on directive.
When to Use Dockerfile vs Docker Compose
Use a Dockerfile When:
- A customised Docker image with environment variables and dependencies must be created.
- Along with your application code, the environment setting should also be version controlled.
- Either you are developing individual containers deployed independently, or your application is in a single container.
Use Docker Compose When:
- You are creating an application that requires several services, such as a web server, database, and cache, to function simultaneously.
- You wish to manage all services as a single unit and define their configuration in a single file.
- Configuring a development environment with several services resembling a production setup is necessary.
How Dockerfile and Docker Compose Work Together
Although they have separate uses, Dockerfile and Docker Compose are frequently combined in practical applications. For every service specified in the docker-compose.yml file, an image is created using a Dockerfile. Subsequently, Docker Compose handles the orchestration of these images as containers, network creation, and service linkage according to specifications.
For example, an application that uses microservices might have separate Dockerfiles for each service that uses it to produce an image. Then, you specify how these services share data, communicate across the network, and interact using Docker Compose.
Conclusion
Anyone using Docker must understand the distinctions between Dockerfile and Docker Compose. Dockerfile focuses on building and configuring a single Docker image, while Docker Compose handles the orchestration of multiple containers and their interactions. Resources from The Knowledge Academy can help you understand when and how to use these tools together, significantly enhancing your development and deployment workflows and making your applications more robust.
