cloud config explained

cloud-config explained

The cloud-config file contains all the configuration to add a new node to your cluster.

Host basic setting

The beginning of the file sets the hostname and ssh key

Etcd setting

Declare the configuration of the etcd cluster. I prefer to use DNS discovery as it has a more permanent and controlable aspect than etcd Discovery while being more maintenable than static discovery. More about this subject can be found in the official documentation

Units

This declares all the services to run at startup

etcd2 and fleet

Not much to say, it just starts them at boot.

data.mount

This mounts a shared NFS data folder. It allows all the user services to find their persistent data in one location: /data.

settimezone.service

This sets the correct time on the server for my area. If you live in GMT you can skip that.

consul.service

Starts consul service, it share the network with the host. It also try to connect to other servers declared on the server.example.com DNS. If it cannot reach it, it will try again.

-advertise ${COREOS_PRIVATE_IPV4} is used to tell consul which IP address should be advertise for the local services. If you don't use this parameter, you might end up having consul advertise localhost or 127.0.0.1 which doesn't make any sense from another node points of view.

registrator.service

Automatically register/deregister docker services as they come and go. Use -e SERVICE_NAME= and -e SERVICE_TAGS= on your docker run to tell haproxy how to serve your services. If no SERVICE_TAGS is provided, the service will be available on all domains reaching haproxy. You can find more about the registrator on the official documentation.

For example, this:

docker run --name webserver -p 80 -e SERVICE_80_NAME=www -e SERVICE_TAGS=example_com httpd

Will make the web-server reacheable from querying www.example.com. The underscore in SERVICE_TAGS=example_com is just a hack done for compatibility reason. You can serve the same service on multiple domain by listing them: SERVICE_TAGS=example_com,example_net.

haproxy.service

Uses consul's data to serve every service as a subdomain on port 80 or 443. It is based on haproxy-consul but it uses here another consul.tmpl to allow for multi-domain support. If you don't want haproxy to act as an SSL termination just remove or comment out bind *:443 ssl crt /certs/ (L16 of consul.tmpl)