Where does libcontainer stand in docker stack?

Question

The typical docker container stack known to me is docker(client) -> dockerd -> containerd -> runC. Then you also hear about libcontainer. I am wondering where libcontainer fits in the above stack and what is it role/purpose.

Answer 1

Short answer:

What had started at github.com/docker/libcontainer
now seems to continue at github.com/opencontainers/runc/tree/master/libcontainer

which means that we now have: docker → containerd → runc → libcontainer

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A bit of history

Parts from: A history of low-level Linux container runtimes follow.

At the beginning:

...the upstream Docker developers, including some members of my Red Hat team, decided they wanted a golang-native way to launch containers, rather than launching a separate application. Work began on libcontainer, as a native golang library for launching containers...

and after the Open Container Initiative (OCI) was formed:

...The libcontainer parts of Docker were broken out and donated to the OCI. The upstream Docker engineers and our engineers helped create a new frontend tool to read the OCI Runtime Specification JSON file and interact with libcontainer to run the container. This tool, called runc, was also donated to the OCI.

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Further reading:

• A Brief History of Containers: From the 1970s Till Now
• Demystifying container runtimes
• What's Up With All The Different Container Runtimes? - Ricardo Aravena, Branch Metrics from KubeCon Europe 2018