CoreOS is a new and existing os promising to simplify how we manage modern software stacks. This presentation tries to explain the most important CoreOS features in 5 minutes. It was presented in a "Israel AWS user group" meetup.

1. CoreOS in 5 minutes

2. What is CoreOS?
○ A minimal Linux built to run docker/rocket containers
○ Rethinking how a modern os for a datacenter should look like
○ Doesn’t have a package manager, (almost) everything is a
container
○ Facilitates atomic os updates
○ Packages cluster coordination/bootstrap tools: etcd, fleet, coreos-
cloudinit

3. CoreOS Host Components
fleetd
systemd
docker
etcd
update-engine
- Init system
- Cluster level orchestration
- Key/Value store for service
discovery and shared configuration
coreos-01

4. CoreOS Unit
[Unit]
Description=ElasticSearch service
After=docker.service
Requires=docker.service
[Service]
ExecStart=/bin/bash -c '/usr/bin/docker run --rm --name %p-%i --publish 9200:9200 --volume /data/elasticsearch:
/data
$(/usr/bin/etcdctl get /services/elasticsearch/config/image)'
ExecStop=/usr/bin/docker stop %p-%i
[X-Fleet]
X-Conflicts=%p@*.service
MachineMetadata=profile=elasticsearch

5. CoreOS release channels
○ Separated release channels: stable, beta, alpha
○ There are different update strategies:
○ Etcd-lock: No more than X instances at a time
○ Off
○ Reboot
○ Rollback won’t work on ec2 without an instance restart

6. Observations
○ Not all CoreOS parameters have sensible defaults
○ Fleet is a very basic scheduler (PR #1055)
○ DNS based service discovery can be added easily with skydns
○ It is hard to “group” dependent services together