feat(ops/modules): configure builderball cache setup

Configures an experimental setup for a builderball-based public cache.

This cache only includes the two build machines (whitby & nevsky), for the time
period where both of them exist simultaneously.

The idea is this:

All participating hosts run a harmonia binary cache locally (whitby already
does). They then run builderball instances pointing at each other's harmonia
caches (through dedicated public hostnames).

When a request comes in, the first matching cache address is returned and Nix
will substitute from there.

Change-Id: Ia7d5357fd5e04f77b460205544fa24e82b100230
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12975
Autosubmit: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

ops/glesys/dns-tvl-fyi.tf

@@ -104,6 +104,40 @@ resource "glesys_dnsdomain_record" "tvl_fyi_net_CNAME" {
   host   = "net"
 }
 
+# Binary cache round-robin setup (experimental; only on .fyi)
+
+resource "glesys_dnsdomain_record" "cache_tvl_fyi_A" {
+  domain   = glesys_dnsdomain.tvl_fyi.id
+  host     = "cache"
+  type     = "A"
+  data     = each.key
+  for_each = toset([var.whitby_ipv4, var.nevsky_ipv4])
+}
+
+resource "glesys_dnsdomain_record" "cache_tvl_fyi_AAAA" {
+  domain   = glesys_dnsdomain.tvl_fyi.id
+  host     = "cache"
+  type     = "AAAA"
+  data     = each.key
+  for_each = toset([var.whitby_ipv6, var.nevsky_ipv6])
+}
+
+# Builderball cache records
+
+resource "glesys_dnsdomain_record" "tvl_fyi_cache_whitby_CNAME" {
+  domain = glesys_dnsdomain.tvl_fyi.id
+  type   = "CNAME"
+  data   = "whitby.tvl.fyi."
+  host   = "whitby.cache"
+}
+
+resource "glesys_dnsdomain_record" "tvl_fyi_cache_nevsky_CNAME" {
+  domain = glesys_dnsdomain.tvl_fyi.id
+  type   = "CNAME"
+  data   = "nevsky.tvl.fyi."
+  host   = "nevsky.cache"
+}
+
 # Google Domains mail forwarding configuration (no sending)
 resource "glesys_dnsdomain_record" "tvl_fyi_MX_5" {
   domain = glesys_dnsdomain.tvl_fyi.id

ops/glesys/dns-tvl-su.tf

@@ -67,6 +67,13 @@ resource "glesys_dnsdomain_record" "tvl_su_sanduny_AAAA" {
   data   = var.sanduny_ipv6
 }
 
+resource "glesys_dnsdomain_record" "cache_tvl_su_whitby_CNAME" {
+  domain = glesys_dnsdomain.tvl_su.id
+  host   = "cache"
+  type   = "CNAME"
+  data   = "whitby.tvl.su."
+}
+
 # Explicit records for all services running on whitby
 resource "glesys_dnsdomain_record" "tvl_su_whitby_services" {
   domain   = glesys_dnsdomain.tvl_su.id

ops/glesys/main.tf

@@ -98,7 +98,6 @@ locals {
     "atward",
     "auth",
     "b",
-    "cache",
     "cl",
     "code",
     "cs",