Support for service namespace in swarm mode

[PanJ]

In Docker >= 1.12, service discovery and load balancing is cool. But there is a use case which I still need while migrating out of Rancher.

In swarm mode, you can create an overlay network and attach it to a service. Then services inside the network will be discovered/load-balanced through DNS queries using service name. The service name must be unique throughout the entire swarm cluster.

What I need is a way to use the same hostname in different services. Let's say we have 2 environment, staging and production. Each of them has 2 services, backend and frontend. frontend service must be able to communicate to backend using http://backend:port/some/path/to/api. In docker swarm, I have to create 2 different services like staging-backend and production-backend. The api must be accessed by http://staging-backend:port/some/path/to/api only.

It would be great if all services connect to a single overlay network by default (service name is unique anyway) and provide a way to define namespace and hostname (must be unique throughout the cluster). Container can access service in the same namespace using hostname, and can access a service across namespace using hostname.namespace, while the unique service_name is still accessible.

This would enhance the flexibility of cluster networking in docker swarm mode. I did not use previous docker swarm before but when I learned about docker swarm mode, I thought that it is the way container orchestration should be (native and complete).

If there is any existing solution or workaround, I really would like to know. In the meantime, I guess I have to refactor the code to make it compatible with docker swarm mode.

Thanks!

[thaJeztah]

Perhaps implementing --network-alias or similar would be a start; there's already an issue for tracking that; #24787

[PanJ]

Thanks for pointing out! After looking through docker run command options, --network-alias is really the closest one.

Anyway, ability to resolve something like <service-name>.<namespace> or even <task-id>.<service-name>.<namespace> is something very useful.