Support TCP, not just HTTP

[lukebond]

@enzor you had some ideas on this I think?

[rcmorano]

@lukebond HAProxy is a TCP balancer aswell, where's your limitation?

[lukebond]

Just a matter of getting around to learning how to do it :)

[lukebond]

The routing is based on HTTP host header at the moment. Not sure how else to route requests to the correct service.

[rcmorano]

I had some [1][2] examples saved in my pocket.com for load balancing mysql TCP connections. Hope them helps as example of HAProxy's TCP mode.

You know I had dns-sd in mind, so [if I'm understanding well what you mean by routing] I think that routing could be then delegated to the rr-dns response for a concrete service.

I'll try to illustrate it with a minimal DNS entries scaffold:

• mysql-service-1.paz.local could be a rr-dns entry resolving to the prioritized/weighted hosts resolved by a SRV record like:
  • __mysql-service-1_lb.tcp.paz.local (which would resolve a list of HAProxy instances for the service)

This way, apps/clients can override the need of supporting SRV records which would be used only for service discovery and the only management needed by Paz would be adding/removing entries to a DNS zone [with low TTL values].

Load balancer instances could get configured querying its own backends via a SRV record like __mysql-service-1.tcp.paz.local.

[lukebond]

@rcmorano thanks for the info!

with the new Docker networking stuff and my conflicted thoughts thereon (see [https://github.com/paz-sh/paz/issues/33#issuecomment-115380577]), i wonder if we need to make a decision re Docker networking before we proceed much further regarding modifications to HAProxy.