Container Basics: Docker and Linux Containers

Understanding Container Basics: An Introduction to Docker and Linux Containers

In the evolving world of software development and deployment, containerization has become a critical skill. Containers enable developers to package applications with all their dependencies and deploy them uniformly across various environments. Two of the most prominent technologies enabling this are Docker and Linux Containers (LXC/LXD). In this article, we delve into the basics of these technologies and provide practical guidance on getting started with both on different Linux distributions.

What is Docker?

Docker is a platform that simplifies the process of building, running, and managing containers. It uses Docker Engine, which is a client-server technology that creates and runs containers based on Docker images. These images are lightweight, standalone, executable packages that include everything needed to run a piece of software, including the code, runtime, libraries, environment variables, and configuration files.

What are Linux Containers?

Linux Containers (LXC) is another lightweight virtualization method that runs multiple isolated Linux systems (containers) on a single control host. LXC combines the kernel's cgroups functionality to provide sandboxing and kernel namespaces to isolate the application's view of the operating environment, including process trees, network, user IDs, and mounted file systems.

LXD is a newer tool built on top of LXC that provides a more user-friendly approach to manage the containers through a RESTful API. It adds advanced features such as snapshotting, live migrations, and storage management.

Installing Docker

The installation process for Docker can vary depending on your Linux distribution. Below are instructions for installing Docker using different package managers such as apt (for Debian/Ubuntu), dnf (for Fedora), and zypper (for openSUSE).

Using apt on Debian/Ubuntu:

1. Update your package index: bash sudo apt update
2. Install packages to allow apt to use a repository over HTTPS: bash sudo apt install apt-transport-https ca-certificates curl software-properties-common
3. Add Docker’s official GPG key: bash curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
4. Set up the stable repository: bash sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
5. Install Docker CE: bash sudo apt update sudo apt install docker-ce

Using dnf on Fedora:

1. Install Docker: bash sudo dnf -y install dnf-plugins-core sudo dnf config-manager --add-repo https://download.docker.com/linux/fedora/docker-ce.repo sudo dnf install docker-ce
2. Start and enable Docker service: bash sudo systemctl start docker sudo systemctl enable docker

Using zypper on openSUSE:

1. Add the Docker repository: bash sudo zypper addrepo https://download.docker.com/linux/suse/x86_64/stable docker-ce
2. Install Docker: bash sudo zypper install docker-ce
3. Start and enable Docker service: bash sudo systemctl start docker sudo systemctl enable docker

Installing and Managing LXC/LXD on Linux

Debian/Ubuntu:

1. Install LXD: bash sudo apt install lxd lxd-client
2. Add your user to the LXD group: bash sudo usermod -a -G lxd $USER
3. Initialize LXD: bash lxd init

Fedora:

Fedora does not include LXD by default, but you can still use LXC. 1. Install LXC: bash sudo dnf install lxc lxc-templates 2. Configuration and running: bash sudo lxc-create -n mycontainer -t download -- -d ubuntu -r focal -a amd64 sudo lxc-start -n mycontainer

openSUSE:

1. Install LXD: bash sudo zypper install lxd sudo lxd init
2. Ensure group permissions are configured properly.

Conclusion

Both Docker and Linux Containers offer powerful options for managing and deploying applications in isolated environments. Whether you choose Docker for its ease of use and extensive features or LXC/LXD for running lightweight Linux systems, understanding how to use these tools is crucial for modern system administration and development work.