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% Build your own Pod

$ whoami

  • Florian Arthofer
  • Cloud Platform Engineer @ Dynatrace
  • @arthfl on GitHub, Twitter...etc

Why?

  • Understanding things on a very low level, helps you debugging the silly problems

What is a container?

  • Containers are just an abstract concept to describe the usage of namespaces and cgroups to run isolated processes

Namespaces

  • What you see
  • man namespaces

CGroups

  • What you can use
  • man cgroups

What is a Pod?

  • The smallest deployable unit of computing in K8S
  • A pod is a group of one or more containers, with shared storage/network, and a specification for how to run the containers

Toolbox

  • runc: CLI tool that implements the OCI standard
    • Used by Docker, Cloud Foundry, Kubernetes...etc
  • iproute2: default userspace utils for Linux networking
  • (This is not the lowest level to create containers)

Create a simple OCI container

  • Create spec file with runc spec
$ runc spec
  • Create root filesystem
$ mkdir rootfs
$ docker export $(docker create alpine:latest) | tar -C rootfs -xvf -
  • Run it!
$ runc run thecontainer

Where is my network?

  • With our simple config, there is no network
  • We have to set up everything ourself :-)

Configure basic network

  • Create a bridge
  • Create a network namespace
  • Patch container into bridge
  • Tell container about network namespace

A simple pod

  • Same network setup
  • Just put two containers in the same network namespace
  • Both see the same interface and can use it alternatingly

A pod with a shared "volume"

  • Both containers have /srv/somevolume, which is a bind-mount to the hosts /tmp/somevolume
  • They are now able to access and write the same files

Conclusion

  • I'm really glad somebody automated all of that already

Questions?

  • ?

Sources