Set up /api/rest_v1/ entry point for restbase

Authored by GWicke.

Description

Set up /api/rest_v1/ entry point for restbase

There are major performance benefits in minimizing the number of domains we
use to serve content. As documented in T95229, total cold-start overheads for
a new domain (DNS, TCP & TLS) seem to exceed 1s with mean VE user's connection
latencies.

This patch sets up a path-based entry point for the REST API at /api/rest_v1/,
which avoids this issue by sharing the existing connection(s) to the main
project domain. Requests matching ^/api/rest_v1/ are diverted to the restbase
cluster in the backend Varnishes. While there might be performance advantages
in doing this in the frontend Varnish (especially for esams, where we'd reduce
the number of Varnish hops from 3 to 1), other considerations like IPSec make
traversing the second layer more practical for now.

Additional minor tweaks:

  • Configure beta labs restbase instance

Bug: T95229

Change-Id: I46e422825af2cf6f972b64e6d50040220ab08995

Details