Chapter 4. Host Grouping Concepts
Apart from the physical topology of Capsule Servers, Red Hat Satellite provides several logical units for grouping hosts. Hosts that are members of those groups inherit the group configuration. For example, the simple parameters that define the provisioning environment can be applied at the following levels (for more information on the use of parameters, see Parameters in the Puppet Guide):
Global > Organization > Location > Domain > Host group > Host
The main logical groups in Red Hat Satellite are:
- Organizations – the highest level logical groups for hosts. Organizations provide a strong separation of content and configuration. Each organization requires a separate Subscription Manifest, and can be thought of as a separate virtual instance of a Satellite Server. Avoid the use of organizations if a lower level host grouping is applicable.
- Locations – a grouping of hosts that should match the physical location. Locations can be used to map the network infrastructure to prevent incorrect host placement or configuration. For example, you cannot assign a subnet, domain, or compute resources directly to a Capsule Server, only to a location.
- Host groups – the main carriers of host definitions including assigned Puppet classes, Content View, or operating system. Find the complete list of host group parameters in Parameters in the Puppet Guide. It is recommended to configure the majority of settings at the host group level instead of defining hosts directly. Configuring a new host then largely becomes a matter of adding it to the right host group. As host groups can be nested, you can create a structure that best fits your requirements (see Section 4.1, “Host Group Structures”).
- Host collections – a host registered to the Satellite Server for the purpose of subscription and content management is called content host. Content hosts can be organized into host collections, which enables performing bulk actions such as package management or errata installation.
Locations and host groups can be nested, organizations and host collections are flat.
4.1. Host Group Structures
The fact that host groups can be nested to inherit parameters from each other allows for designing host group hierarchies that fit particular workflows. A well planned host group structure can help to simplify the maintenance of host settings. This section outlines four approaches to organizing host groups.
Figure 4.1. Host Group Structuring Examples
The advantage of a flat structure is limited complexity, as inheritance is avoided. In a deployment with few host types, this scenario is the best option. However, without inheritance there is a risk of high duplication of settings between host groups.
Life Cycle Environment Based Structure
In this hierarchy, the first host group level is reserved for parameters specific to a life cycle environment. The second level contains operating system related definitions, and the third level contains application specific settings. Such structure is useful in scenarios where responsibilities are divided among life cycle environments (for example, a dedicated owner for the Development, QA, and Production life cycle stages).
Application Based Structure
This hierarchy is based on roles of hosts in a specific application. For example, it enables defining network settings for groups of back-end and front-end servers. The selected characteristics of hosts are segregated, which supports Puppet-focused management of complex configurations. However, the content views can only be assigned to host groups at the bottom level of this hierarchy.
Location Based Structure
In this hierarchy, the distribution of locations is aligned with the host group structure. In a scenario where the location (Capsule Server) topology determines many other attributes, this approach is the best option. On the other hand, this structure complicates sharing parameters across locations, therefore in complex environments with a large number of applications, the number of host group changes required for each configuration change increases significantly.