We recently switched (like 2 weeks ago) our project from deployment on ubuntu servers via 'git pull' managed with supervisord to docker/coreos/fleet, and it's been epic. While coreos is built for large clusters, we run a 3 host cluster in ec2, and couldn't be happier. We switched from multiple servers running 1 instance of each service to load balancing all instances on these 3 hosts. This increased uptime, made deployment and management easier, and gave us the benefits of docker as well (verifying things work locally).<p>There's only 2 real problems, both of them very minor:<p>* fleet managing state. We've had to manually kill containers sometimes, and destroy systemd services before we could start it again.<p>* all EC2 amis use ebs backed instances. We haven't used a higher-IOPs ebs backed instance because the only delay we see are in startup times (which doesn't matter, just longer rolling deploys). But an instance-backed ami would be nice.