Docker Swarm and Consul production setup recommendation

dockerdocker-swarmhigh-availability

I'd like to set up a production HA Docker Swarm cluster.

Docker Swarm needs a Key Value store as a precondition, consul in this case.

Now I'm asking what a clever setup would be:

Consul should run in Docker containers
Consul must be HA and automatically scaleable
Consul containers should be managed with Docker Swarm (this would need consul running though)

Constraints

Running consul on the host is not an option
Having to manage consul containers manually is not an option
Docker Swarm with a Docker Hub token is not an option

Approach

Any ideas how this chicken or the egg problem can be solved in a clean and reliable manner for efficient operation?

Multiple swarm instances would certainly look like a reasonable approach but how to setup the initial swarm without consul and swarm? Thanks.

Best Answer

Jacob Blain Christen has a nice article about this very problem. In short: start the docker daemon with a reference to the not yet existing consul cluster, then start consul via docker. Citation:

Fortunately, the Docker daemon will happily retry to connect to the cluster-store aka the KVS every so often, this gives us time to underlay it via Docker Compose.

Hope this helps.

Related Solutions

Docker – In a container cluster like Kubernetes or Docker 1.12 Swarm, how do you resolve with external DNS to the good container on the good host

Docker 1.12 with swarm-mode comes with built-in load balancing.

In your case, the primary benefit of that is that you don't have to dynamically update your DNS depending on what host a particular container ends up running on (which would most likely lead to disaster anyway, because of DNS ttl and caching).

Say for example you ran:

docker service create --name nginx -p 80:80 nginx

That will create a nginx service with one replica, so a single container will be started on a random host in your swarm. But the built-in load balancing will route requests on port 80 on any of the swarm hosts to the host where the container is run. And similarly if you scale the service with:

docker service scale nginx=2

That makes for a very simple setup:

Use the DNSMadeEasy round-robin feature and add A records for all the host IPs in your swarm.
Deploy your app with docker service create
Profit

From your question, it sounds like you'd like to run multiple sites on your swarm, eg. multiple apps all listening on port 80 and port 443. As @Flippy points out, to do that you currently have to run a layer 7 loadbalancer like HAProxy or nginx that inspects request host-headers and forwards requests appropriately. This is also simple to do with Docker 1.12 Swarm mode and this is a good getting started guide.

Docker swarm and volumes

Yes this does work, and using the global flag will be a better option to prevent any conflicts. I have run a similar model to this with MongoDB as a test and worked perfectly.

Best Answer

Related Solutions

Docker – In a container cluster like Kubernetes or Docker 1.12 Swarm, how do you resolve with external DNS to the good container on the good host

Docker swarm and volumes

Related Topic