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Manage Linux containers with Docker

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Article from ADMIN 16/2013

By Rob Knight

The Docker software can pack and run any application as a lightweight container – including web applications.

Docker is a new open source tool [1] designed to change how you think about cloud deployments. It provides functionality to create and manage virtual machine images that can be shared, modified, and easily deployed to bare metal servers, cloud hosts, or local environments. The technology that Docker depends on is present in recent Linux kernels, meaning that you can use Docker on any machine running a recent kernel [2]. Docker promises to enable "run anywhere" deployments for a wide class of applications that have previously been very hard to package and maintain.

Container Ship

For example, a typical LAMP-stack application might depend on a specific version of PHP, a particular Apache configuration, or the installation of certain operating system packages. Deploying the application to varied platforms can be difficult because of differences in package management or conflicts with the configuration used by other applications running in the same environment.

Docker's approach is to isolate components inside "containers," allowing your Apache process to have its own copy of the operating system, free from conflicts with other processes. These containers can be saved as "images" that can be worked on locally, shared with others, and ultimately deployed on your servers. Instead of requiring a correctly configured environment in which to run, your application can be deployed with a container that provides everything it needs.

The key technology enabling this approach is LXC, or Linux Containers [3]. Unlike a hypervisor-based virtual machine like Xen, LXC doesn't provide a full virtual machine with hardware emulation; instead, it provides a separate process space and network interface for applications

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