6.2. Capacity Planning and Districts

Red Hat recommends that you plan for your OpenShift Enterprise deployment's expected capacity to better ensure resource availability for gears. This is best accomplished through the use of districts. Districts facilitate gear movement between node hosts in order to manage resource usage. Districts also allow node deactivation to ensure a node receives no additional gears.

Note

Red Hat requires using districts to provide several administrative benefits. Districts are difficult to introduce after the initial OpenShift Enterprise deployment process, therefore it is required to create districts before creating any applications.

See Also:

6.2.1. Hierarchy of OpenShift Enterprise Entities

To better understand the role of districts, examine their relationship with other OpenShift Enterprise entities:

Table 6.1. OpenShift Enterprise Container Hierarchy

Entity Description
Gears Gears are at the bottom of the hierarchy, and contain instances of one or more cartridges.
Nodes Nodes contain gears. Each gear UUID has a local UNIX user UID on the node host with storage and processes constrained by various mechanisms.
Districts When used, districts contain a set of nodes, including the gears that reside on them.
Node profiles Node profiles are at the top of the hierarchy, and are also referred to as gear profiles or gear sizes. They are conceptually similar to a label attached to a set of nodes. Node profiles are assigned to districts, and all nodes in a district must have that node profile. Nodes or districts can only contain gears for one node profile.
Applications Applications contain one or more gears, which currently must all have the same node profile. Application gears can span multiple nodes in multiple districts. However, no mechanism exists for placing gears on specific nodes or districts.