Draft: custom serivce

[nigoroll]

This is a draft of an idea to generalize #138, implementing #132

As of this initial comment, there is no implementation, just a proposed VCC interface.

My expectation would be that this should allow to share code with the existing service implementation (which queries SRV records), because the resulting structure should be identical.

Copying the central example from the VCC draft, this would implement:

  acl ip6 { "::"/0; }

  sub vcl_init {
    new mysrv = dynamic.custom_service();
    mysrv.add_preferred("my.backend.example.com", acl=ip6);
  }

as a shorthand of

  acl ip6 { "::"/0; }

  sub vcl_init {
    new mysrv = dynamic.custom_service();
    mysrv.add("my.backend.example.com", if=match, acl=ip6, priority=0);
    mysrv.add("my.backend.example.com", if=nomatch, acl=ip6, priority=1);
  }

with .add() allowing for fine grained control, enabling other use cases, like preferring a local datacenter over a remote one.

Note that the proposal also includes support for the weight attribute, such that multiple A/AAAA/CNAME records can be added for load balancing.

[thomasklinger1234]

@nigoroll just a follow up questions on this design:

from my reading on SRV records, it should already contain the priority and weight per entry. so I would assume that anyone using SRV records with libvmod-dynamic would handle preferences at the DNS server level.

so the point of this proposal is to mimick the way that SRV records are designed but bring the concept to A/AAAA/CNAME records, right?

[nigoroll]

so the point of this proposal is to mimick the way that SRV records are designed but bring the concept to A/AAAA/CNAME records, right?

Exactly that, with the intend of improving code reuse / avoid duplication, while also implementing a proven concept.

[thomasklinger1234]

  acl ip6 { "::"/0; }

  sub vcl_init {
    new mysrv = dynamic.custom_service();
    mysrv.add_preferred("my.backend.example.com", acl=ip6);
  }

sounds alright to me!