Proposal: Create a Way to Find Local Service with DNS Discovery

[ekristen]

In some deployment models like with nsq it is recommended that you run a nsq instance per server and all applications on that server talk to that nsq instance.

As it stands today I either have to pass the node name or manually specify the port and host to connect to for all apps on the server.

My proposal is that the service tag local is introduced as a reserved tag that when seen by the agent means it looks only locally for that service and returns the appropriate DNS.

Example:

• local.nsqd.service.consul on server01 will return 10.10.100.100
• local.nsqd.service.consul on server02 will return 10.10.100.200
• nsqd.service.consul on server01 will return 10.10.100.100, 10.10.100.200
• nsqd.service.consul on server02 will return 10.10.100.100, 10.10.100.200

To elaborate a little further, the local tag should work like normal, only return DNS record if the service exists on the local agent, and is in a healthy state.

Bottom Line: local would be a special tag that when used would make the agent not consult the entirety of the datacenter and only resolve local services to local agent.

[highlyunavailable]

This is sort of an inverse duplicate of #488 that I asked for a long time ago and sort of related to #252 I think.

[slackpad]

#2137 will let you do this using a simple prepared query definition (and with prepared query templates you can create a single template definition that'll cover all your services).