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Chapter 2. Configuration Basics

Table of Contents

2.1. Configuration Layout
2.2. The Current State of the Cluster
2.3. How Should the Configuration be Updated?
2.3.1. Editing the CIB Using XML
2.3.2. Quickly Deleting Part of the Configuration
2.3.3. Updating the Configuration Without Using XML
2.4. Making Configuration Changes in a Sandbox
2.5. Testing Your Configuration Changes
2.5.1. Small Cluster Transition
2.5.2. Complex Cluster Transition
2.6. Do I Need to Update the Configuration on All Cluster Nodes?

2.1. Configuration Layout

The cluster is defined by the Cluster Information Base (CIB), which uses XML notation. The simplest CIB, an empty one, looks like this:

Example 2.1. An empty configuration

<cib crm_feature_set="3.0.7" validate-with="pacemaker-1.2" admin_epoch="1" epoch="0" num_updates="0">

The empty configuration above contains the major sections that make up a CIB:
  • cib: The entire CIB is enclosed with a cib tag. Certain fundamental settings are defined as attributes of this tag.
    • configuration: This section — the primary focus of this document —  contains traditional configuration information such as what resources the cluster serves and the relationships among them.
      • crm_config: cluster-wide configuration options
      • nodes: the machines that host the cluster
      • resources: the services run by the cluster
      • constraints: indications of how resources should be placed
    • status: This section contains the history of each resource on each node. Based on this data, the cluster can construct the complete current state of the cluster. The authoritative source for this section is the local resource manager (lrmd process) on each cluster node, and the cluster will occasionally repopulate the entire section. For this reason, it is never written to disk, and administrators are advised against modifying it in any way.
In this document, configuration settings will be described as properties or options based on how they are defined in the CIB:
  • Properties are XML attributes of an XML element.
  • Options are name-value pairs expressed as nvpair child elements of an XML element.
Normally you will use command-line tools that abstract the XML, so the distinction will be unimportant; both properties and options are cluster settings you can tweak.