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CoreOS


I have started learning Kubernetes for last few months now. While learning this, I had come across a beautiful concept of etcd. Doing further research on etcd I came to know that it has come from CoreOS. The latest I hear is etcd will now be part of CNCF (Cloud Native Compute Foundation). 

So some basic information I gathered about CoreOS is here.
  1. CoreOS is sometimes referred to as Container Linux
  2. CoreOS is a linux distribution
  3. It does not have a package manager, so nothing like yum or apt-get
  4. CoreOS took inspiration from Chrome browser, so they push all the required updates automatically.
  5. Only containers can run on CoreOS
  6. CoreOS at best works with multiple machines (like a cluster)
  7. Fleet is used to bring systems together to form a cluster
  8. Fleet is now discontinued in favor of Kubernetes
  9. etcd is a distributed key value data store. It can be used for storing configuration values, service discovery etc


CoreOS is building many components that work well with for Kubernetes
  • etcd
    • A distributed key value data store
    • High available
    • Typical use cases are storing configuration information, service discovery etc
    • etcd when used with 'registrator' stores docker containers information running on the host. This information can be the IP address and Port to easily discover the services running on the host.
  • flanneld
    • flanned is used for configuring layer 3 network fabric for Kubernetes
    • flannel runs as a small binary agent on each host and is responsible for allocating a  subnet lease to each host out of the larger pre-configured address space
    • flannel control the traffic flow between hosts, it does not control how the containers are networked to hosts
    • Learn more about flannel here: https://github.com/coreos/flannel
  • rkt
    • Container engine
    • Basic unit of execution is Pod
    • With rkt architecture pods will  run directly in the classical unix process model.
    • So pods can be managed with systemd service
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