rkt had features ahead of its time that differentiated it from Docker and the other early runtimes. Most of the functionality was gradually replicated in Docker's libcontainer by the LMCTFY developers.ĬoreOS, after initially exclusively using Docker in their Container Linux product, created an alternative to Docker called rkt. Google also open sourced a version of their internal container stack, LMCTFY, but abandoned it as Docker gained popularity. Before long, Docker dropped LXC, created the "Open Container Initiative" to establish container standards (more on this later), and open sourced some of their container components as the libcontainer project. For example, Canonical's JuJu and Docker (briefly) were notable tools built on top of LXC.ĭocker (at the time, "dotCloud"), began building tooling around LXC to make containers more developer and user friendly. Neither LXC nor systemd-nspawn really caught on with end-users, but they did see some use in other systems. Systemd also gained similar container support- systemd-nspawn could run namespaced processes and systemd itself could control cgroups. LXC, Linux Containers, was introduced shortly after cgroups and was designed for "full-system" containers. What is a container runtime?Īfter cgroups were added to the Linux kernel in 2007, several projects emerged that took advantage of them by creating containerization processes: Instead of unshare-ing, cgcreat-ing, and s emodul-ing custom namespaces, cgroups, and selinux policies every time we want to create a new isolated process, these components have been bundled together in a concept called a "container." Tools we call "container runtimes" make it easy to compose these pieces into an isolated, secure execution environment that we can deploy in a repeatable manner.įor more information about containers themselves, check out our other post What is a container? Definition, benefits and use cases. Simplifying process isolation: containers and container runtimes This is great, but doing all of this manually each time we want to create a new isolated process would be tiresome. Together, these kernel primitives allow us to set up secure, isolated, and metered execution environments for our processes. Containers are fundamentally composed of several underlying kernel primitives: namespaces (who you are allowed to talk to), cgroups (the amount of resources you are allowed to use), and LSMs (Linux Security Modules-what you are allowed to do). Before dissecting container runtimes, let's quickly recap containers.Ĭontainers are not first-class objects in the Linux kernel.
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