Abstract: Techniques for server movement control are described. A capacity library service (CLS) can manage which hosts in a provider network can be taken in and out of production. The CLS may also control which entities may remove hosts from production and under what conditions the hosts may be removed from production. In some embodiments, the CLS can execute various workflows to manage checkout and check-in of hosts. Workflows may also be used to manage hosts while they are out of production to manage state transitions (e.g., in production, in testing, in reserve, etc.) based on current host fleet capacity and checkout rules.