CoreOS service discovery using flannel, etcd and SkyDNS.

discovery@.service

[Unit]
Description=Service discovery for %i
After=%i.service
Requires=%i.service

[Service]
Restart=always
Environment="SLEEP=5"
Environment="TTL=10"
Environment='FORMAT="{{ .NetworkSettings.IPAddress }}"'
ExecStartPre=-/usr/bin/echo Starting watcher
ExecStart=/bin/sh -c "while sleep ${SLEEP}; do SERVICE_NAME=$(echo %i | cut -d @ -f1); INSTANCE_NAME=$(echo %i | cut -d @ -f2); IMAGE_NAME=$(echo %i | tr -d @); IP=$(docker inspect --format ${FORMAT} $IMAGE_NAME); echo Refreshing IP of $IMAGE_NAME; etcdctl set --ttl ${TTL} /skydns/yourdomain/$SERVICE_NAME/$INSTANCE_NAME '{\"host\":\"'$IP'\"}'; done;"

[X-Fleet]
MachineOf=%i.service

skydns.service

[Unit]
Description=SkyDNS
After=docker.service
Requires=docker.service

[Service]
Restart=always
TimeoutStartSec=600s
EnvironmentFile=/etc/environment
ExecStartPre=-/usr/bin/docker rm -f skydns
ExecStartPre=/usr/bin/docker pull skynetservices/skydns
ExecStartPre=/usr/bin/etcdctl set /skydns/config '{"nameservers": ["8.8.8.8:53","8.8.4.4:53"]}'
ExecStart=/usr/bin/docker run --rm --name skydns --net host -e "SKYDNS_ADDR=${COREOS_PRIVATE_IPV4}:53" -e "SKYDNS_NAMESERVERS=8.8.8.8:53" skynetservices/skydns -verbose -discover -domain yourdomain
ExecStop=-/usr/bin/docker rm -f skydns

[X-Fleet]
Global=true

user-data

#cloud-config

coreos:
  flannel:
      interface: $public_ipv4
  etcd:
    discovery: https://discovery.etcd.io/generate_your_own
    addr: $public_ipv4:4001
    peer-addr: $public_ipv4:7001
  fleet:
    public-ip: $public_ipv4
  units:
    - name: flanneld.service
      drop-ins:
        - name: 50-network-config.conf
          content: |
            [Service]
            ExecStartPre=/usr/bin/etcdctl set /coreos.com/network/config '{ "Network": "10.3.0.0/16" }'
      command: start
    - name: etcd.service
      command: start
    - name: fleet.service
      command: start
    - name: docker-tcp.socket
      command: start
      enable: true
      content: |
        [Unit]
        Description=Docker Socket for the API

        [Socket]
        ListenStream=2375
        Service=docker.service
        BindIPv6Only=both

        [Install]
        WantedBy=sockets.target