Service discovery topological affinity

[enxebre]

For service to service communication we should be able to put a solution for discovery giving priority to the instances in the same topological domain, e.g a service in az1 should be able to see first services in the same az than services in az2
Something like internal communication proxies with restricted scope per az

[wallies]

so should relate to http://kubernetes.io/docs/user-guide/node-selection/ and https://github.com/kubernetes/kubernetes.github.io/blob/master/docs/user-guide/node-selection/pod-with-node-affinity.yaml

[enxebre]

A way of doing this could be: given a group of slaves with semantic topological metadata, Marathon constraints could use this metadata to distribute and restrict the habitat of a given app/group while consul could use the same info via SERVICE_TAGS to limit the scope of the discovery via "az1.qa.sensitive-service-name.service.consul"