Getting started with Dockerpublished on 1/17/2023
Getting started with Docker
A Dockerfile is a script that contains instructions for building a Docker image. To create a Dockerfile, you will need to have a basic understanding of the command line and the Docker command syntax. Here is an example of a simple Dockerfile:
# Use an official Python runtime as the base imageFROM python:3.8-slim-buster# Set the working directory in the containerWORKDIR /app# Copy the requirements file into the containerCOPY requirements.txt .# Install the required packagesRUN pip install --no-cache-dir -r requirements.txt# Copy the rest of the application code into the containerCOPY . .# Make port 80 available to the world outside the containerEXPOSE 80# Define the command to run when the container startsCMD ["python", "app.py"]
FROMinstruction sets the Base Image for subsequent instructions.
WORKDIRinstruction sets the working directory.
COPYinstruction copies new files or directories in the container.
RUNinstruction will execute any commands in a new layer on top of the current image and commit the results.
EXPOSEinstruction informs Docker that the container will listen on the specified network ports at runtime.
CMDinstruction provides default command, which will be executed only when you run the container
You can build the image using the command
docker build -t <image_name> .
It is important to note that a Dockerfile should be named
Dockerfile and should be located at the root of the directory containing the rest of the files for the application.
Here are some best practices for creating a Dockerfile:
- Use a minimal base image: Use a minimal base image that contains only the necessary dependencies for your application. This will help keep the image size small and reduce the attack surface.
- Use the
.dockerignorefile: Use a
.dockerignorefile to exclude files and directories that do not need to be included in the image. This will help keep the image size small and reduce build time.
- Use multi-stage builds: Multi-stage builds allow you to use multiple
FROMinstructions in a single Dockerfile. This can be used to build your application in one stage and then copy the necessary files to a smaller runtime image in another stage.
- Use environment variables: Use environment variables to configure your application at runtime instead of hardcoding values in the Dockerfile.
- Run a single process per container: Each container should be designed to run a single process, and that process should handle the majority of the container's responsibilities.
- Keep the Dockerfile simple and easy to understand: Keep the Dockerfile simple and easy to understand so that it is easy to maintain and troubleshoot.
- Keep the container updated: Keep the container updated with the latest security patches and software versions.
- Keep the container small: Keep the container small by limiting the number of installed packages and removing unnecessary files.
- Limit the number of layers: Limit the number of layers by combining commands together when possible.
- Avoid using
latesttag: Avoid using
latesttag when specifying the version of a base image, instead use explicit version number to prevent unexpected changes.
Docker Compose is a tool for defining and running multi-container Docker applications. To create a
docker-compose.yml file, follow these steps:
- Create a new directory for your project and navigate into it.
- Create a new file called
docker-compose.ymlin the project directory.
- In the
docker-compose.ymlfile, define your application's services, networks, and volumes.
- Use the
docker-composecommand-line tool to build, run, and manage your application.
Here is an example of a
docker-compose.yml file that defines a simple web service and a database service:
version: '3'services:web:build: .ports:- "8000:8000"depends_on:- dbdb:image: postgresenvironment:POSTGRES_USER: examplePOSTGRES_PASSWORD: examplevolumes:- db-data:/var/lib/postgresql/datavolumes:db-data:
To start the services defined in this
docker-compose.yml file, run the following command:
You can also use
docker-compose down to stop and remove the containers, networks, and volumes created by
You can find more information and examples in the official Docker Compose documentation: https://docs.docker.com/compose/
Docker network and volume
In Docker, a network is a virtual interface that allows containers to communicate with each other and with the host system. By default, each container is connected to a network called
bridge, but you can also create custom networks to control how containers interact with each other.
A volume is a way to store data outside of a container's filesystem. This allows data to persist even if the container is deleted, and also allows multiple containers to share the same data. Volumes can be created and managed using the
docker volume command.
docker-compose.yml file, you can define the networks and volumes for your application's services. Here is an example of how to define a custom network and a volume in a
version: '3'services:web:build: .networks:- mynetworkvolumes:- myvolume:/appnetworks:mynetwork:volumes:myvolume
In this example, the
web service is connected to a network called
mynetwork and is using a volume called
myvolume to store data in the
You can also use the
docker network and
docker volume commands to manage networks and volumes outside of
You can find more information and examples in the official Docker documentation:
- Networks: https://docs.docker.com/network/
- Volumes: https://docs.docker.com/storage/volumes/
Docker network types
Docker supports several types of networks, each with its own unique features and use cases. The most commonly used network types are:
bridge: This is the default network type in Docker. It creates a virtual network between the host and the containers, allowing them to communicate with each other and with the host system. Containers on the same bridge network can see and communicate with each other, but they cannot communicate with containers on other networks.
host: This network type allows a container to use the host's network stack. This means that the container shares the host's IP address and network configuration. This is useful for scenarios where you need to access a service running in a container on the host's network.
none: This network type disables all network connections for the container. This is useful for scenarios where you need to run a process that does not need network connectivity, or when you want to configure the container's network stack manually.
overlay: This network type allows you to create a virtual network that spans multiple Docker hosts. This is useful for scenarios where you need to connect containers running on different hosts, such as in a swarm cluster.
macvlan: This network type allows you to assign a unique MAC address to each container, making it appear as a physical host on the network. This is useful for scenarios where you need to give a container its own IP address, or when you want to integrate a container into an existing network infrastructure.
You can find more information and examples in the official Docker documentation: https://docs.docker.com/network/
It's important to note that the network type you choose will depend on the requirements of your application and infrastructure.