If no host is completely free, the HostSelector may return the least-loaded remote machine.

We picked the 20,000 requests per hour number precisely because it effects the fewest applications (less than ten of the hosts we see in our hourly report of high-traffic consumers of our site).

First, remember you are consolidating two somewhat contradictory goals: you want to minimize duplication among containers (and the host) while needing to ensure isolation.