CoreOS

Useful articles:

• https://www.digitalocean.com/community/tutorials/an-introduction-to-coreos-system-components

3 components:

• etcd for shared key-value storage
• docker containers that connect by reading and writing to etcd
• process management with fleet

Vagrant set-up:

Remember:

• add -A when connecting over SSH to forward SSH agent

Tools:

• etcdctl for interacting with etcd (distributed key-value store)
• fleetctl for sending instructions to cluster
• confd for managing config files using templates merged with data from etcd

systemd unit:

• starts Docker container
  • looks for info from etcd to complete template
  • starts elastic search
• puts information into etcd about the running instance (which the Docker container needs before it can start)
• cleans up etcd when the container stops

systemd variables:

• %p -> prefix name (eg 'elasticsearch' from 'elasticsearch@.service')
• %i -> instance name

On CoreOS machine, systemctl acts largely the same as fleetctl.

$ systemctl list-units # show units $ journalctl -f -u $UNIT # show (and follow) journal for a specific unit