Scheduler Hint Extension#

A Scheduler Hint allows a cloud server to be built near to, or far from, an existing server within a specific zone. If a build request with a hint can not be satisfied then the build will not succeed, and the server, which will have a status of ERROR and a task state of scheduling, must be manually deleted.

A zone is a logical container for servers. The Public IP Zone is the zone in which a Public IP can be shared between two or more servers.

Why use scheduler hints?#

The following use cases identify some reasons you might use scheduler hints:

  • Reduce server density - You may have two or more VM’s on the same physical host. By specifying the far parameter, you may mitigate risk.

  • Mitigate impact of maintenances - If Rackspace needs to reboot all servers for maintenance, specifying the far parameter, helps to ensure that all servers aren’t affected at once.

  • Build servers in the same ‘Public IP zone’ (cell) - In order to share an IP between two servers they need to be in the same Cell, by specifying the near parameter.

  • Build servers to achieve lowest latency: If you have certain applications that are sensitive to latency and want to build components of those as close to one another as possible, specify the near parameter. This might lower availability.

  • Build servers to achieve higher availability: If you need to ensure parts of your application are as far away from each other as possible, specify the far parameter. This might increase latency.

Scheduler hint operations#

For an example of this operation, see Create server with scheduler hint.