> I haven't yet found any good way to prioritize containers co-running on the local host
You may find that RFC3484 helps; it prefers the address with the longest prefix in common with your own address so will tend to pick your own address. And you are probably getting this behaviour already.
Thanks for the pointers! Unfortunately, I don't think this applies. I'm certainly not getting this behavior - I wouldn't have even thought of it if I haven't observed higher latencies resulting from (sub)requests chain jumping from node to node back-and-forth, instead of staying within the node's boundaries.
The problem is, the network space there is flat, not hierarchical - while I haven't looked at the actual implementation code, I believe container addresses are just randomly chosen from a single big 10.42/16 subnet and I'm unaware if there's a way that I can assign hosts, say, a /20 out of that space (yes, this would've solved things nicely).
Oh. Right. I happen to work on a different Docker network, which 'chunks' the address space so containers on the same machine are very likely to have contiguous addresses. Hadn't occurred to me theirs doesn't do that.
You may find that RFC3484 helps; it prefers the address with the longest prefix in common with your own address so will tend to pick your own address. And you are probably getting this behaviour already.