TCP load balancing & failover

A common feature across log forwards is the ability to load balance data across a static number of addresses. For example:

[sink.out]
  type = "tcp"
  addresses = ["1.1.1.1:9000", "1.1.1.1:90001"]

Alternatively, DNS could be used for this when support DNS lookup (https://github.com/timberio/vector/issues/252)

Requirements

• Default load balancing strategy is round robbin.
• Default to a ttl of 30 seconds, ttl is an option the user can adjust. I think 30 seconds is a good default, especially if TLS is enabled. This will reduce the connection setup overhead. Alternatively, we could leave the connection open and balance over those open connections?
• As a follow up, I'd like to consider how we'd solve failover. This could be accomplished by setting the ttl to 0? (ex: this image).

Open questions

1. Does this belong in Vector or is it better solved with DNS or another external system? To me, it seems like a light weight feature that would be useful.
2. Anything else I'm missing.