Docker is an open-source platform that automates the deployment of applications within lightweight and isolated containers. Containers are self-contained execution environments that package applications and their dependencies, ensuring consistency and reproducibility across different environments. Docker allows developers to encapsulate applications, libraries, and configurations into portable and shareable containers. It simplifies the deployment process, as containers can be easily created, distributed, and scaled without worrying about underlying infrastructure.
Module 1: Docker Basics
Introduction to Docker
Docker is an open-source platform that automates deploying, scaling, and managing applications. It does this by isolating applications into separate containers, making it easier to manage and secure your applications while gaining a significant performance boost.
The installation process for Docker varies based on the operating system you are using. Docker provides installation guides for Ubuntu, Windows, and MacOS on their official website.
Your First Docker Container
After Docker is installed, you can start a container with the 'docker run' command. For instance, 'docker run hello-world' would run a simple Hello World container provided by Docker. This command downloads a ready-made image from the Docker Hub, runs the container from that image, and outputs a Hello World message.
A Docker image is a lightweight, stand-alone, executable package that includes everything needed to run a piece of software. Docker images are constructed from layered filesystems and represent executable application container images. Images are stored in a Docker registry such as Docker Hub.
Module 2: Dockerfile and Docker Compose
Creating a Dockerfile
A Dockerfile is a text file that Docker reads to build an image automatically. The Dockerfile specifies the base image and the steps for creating the new image. The steps can include updating the base image, installing new software and libraries, and copying the application code into the image.
Building an Image from Dockerfile
Once the Dockerfile is created, you can build an image from it using the 'docker build' command. The command is typically run as 'docker build -t my-app:latest .', where 'my-app:latest' is the name and tag of the image, and the '.' tells Docker to look for the Dockerfile in the current directory.
Introduction to Docker Compose
Docker Compose is a tool for defining and running multi-container Docker applications. It allows you to create applications that require multiple Docker containers by writing a YAML file. Each service (container) can be configured in this file, and Docker Compose takes care of setting up the network and starting the containers in the correct order.
Running an Application with Docker Compose
Once the Docker Compose YAML file (usually named docker-compose.yml) is created, you can start the application with 'docker-compose up' command. This will start the containers as defined in the Compose file.
Module 3: Networking and Storage
Networking in Docker
Docker networking allows you to define your own network in your containers. It's useful when you want to isolate your containers or need to deal with the networking more closely. Docker provides several networking drivers like 'bridge', 'host', 'none', and 'overlay'.
Storage in Docker
By default, any data created inside the Docker container is only available from within the container and only while the container is running. To persist data, Docker provides volumes. A volume is a designated directory on the host system that bypasses the Union File System, to provide shared storage and persistent data storage for Docker containers.
Docker volumes are the preferred way of handling persistent data created by and used by Docker containers. Volumes can be more safely shared among multiple containers and can be used with Docker Compose. They can be created with the 'docker volume create' command and then attached to containers via the 'docker run' command.
Docker Bind Mounts
Bind mounts are another option for persisting data generated by and used by Docker containers. Bind mounts have been around since the early days of Docker. Bind mounts have limited functionality compared to volumes, but are very performant. They can be created with the 'docker run' command by specifying the host path to be mounted.
Module 4: Docker Security and Best Practices
Like any other system, security is an important aspect of Docker. Some security practices include running Docker containers with a non-root user, not using insecure Docker images, keeping Docker up to date, and limiting resources per container.
Docker Best Practices
Some Docker best practices include building small images using .dockerignore files, using multi-stage builds, not installing unnecessary packages, using official images, and tagging your images properly.