How to deploy consul using Docker 1.12 swarm mode

Question

I have a consul cluster of 3 servers. I also have a docker swarm of around 6 workers and 3 masters (the masters are on the same hardware as the consul servers but are set with availability == drain to prevent them accepting work).

I generally use consul-template to read consul K/V. I cannot for the life of me work out how to sensibly roll out a consul agent service. If I use a global service then I get one agent per node but the server cluster complains because the client agents all appear to have the same IP address.

Replicated services seem to be the way to go, but I believe I need to publish the client port 8301 and that seems to cause a clash with my server cluster (which is running both swarm master and consul servers (not under docker).

I'd appreciate a general steer in the right direction - bearing in mind this is 1.12 swarm mode and therefore very different from earlier versions.

Answer 1

For those like me that prefer to run our services from docker-compose.yml files, I managed to "docker stack deploy"

https://github.com/thechane/consul/blob/master/docker-compose.yml

... to run Consul as a Docker service.

--- EDIT , poor form to just answer with links so here it is:

version: '3.1'
#customise this with options from
#https://www.consul.io/docs/agent/options.html

services:

seed:
  hostname: seed
  image: consul:0.8.0
  deploy:
    restart_policy:
      condition: none  #we do not want this to be restarted on timeout (see entrypoint options below)
    replicas: 1
    placement:
      constraints:
        - "engine.labels.access == temp"
        - "engine.labels.access != consul"
  environment:
    - "CONSUL_LOCAL_CONFIG={\"disable_update_check\": true}"
    - "CONSUL_BIND_INTERFACE=eth0"
  entrypoint:
    - timeout     #this seed fires up the cluster after which it is no longer needed
    - -sTERM      #this is the same signal as docker would send on a scale down / stop
    - -t300       #terminate after 5 mins
    - consul
    - agent
    - -server
    - -bootstrap-expect=5
    - -data-dir=/tmp/consuldata
    - -bind={{ GetInterfaceIP "eth0" }}
  networks:
    - "consul"

cluster:
  image: consul:0.8.0
  depends_on:
    - "seed"
  deploy:
    mode: global                                      ##this will deploy to all nodes that
    placement:
      constraints:
        - "engine.labels.access == consul"            ##have the consul label
        - "engine.labels.access != temp"
  environment:
    - "CONSUL_LOCAL_CONFIG={\"disable_update_check\": true}"
    - "CONSUL_BIND_INTERFACE=eth0"
    - "CONSUL_HTTP_ADDR=0.0.0.0"
  entrypoint:
    - consul
    - agent
    - -server
    - -data-dir=/tmp/consuldata
    - -bind={{ GetInterfaceIP "eth0" }}
    - -client=0.0.0.0
    - -retry-join=seed:8301
    - -ui                                              ##assuming you want the UI on
  networks:
    - "consul"
  ports:
    - "8500:8500"
    - "8600:8600"

networks:
  consul:
    driver: overlay

Also note, I later discovered that without the seed more consul instances can not be added. So if you intend to expand your swarm node count I'd remove the timeout command with its options from the seed entrypoint.