3.3. Node Attributes

⁠3.3. Node Attributes

Pacemaker allows node-specific values to be specified using node attributes. A node attribute has a name, and may have a distinct value for each node.

While certain node attributes have specific meanings to the cluster, they are mainly intended to allow administrators and resource agents to track any information desired.

For example, an administrator might choose to define node attributes for how much RAM and disk space each node has, which OS each uses, or which server room rack each node is in.

Users can configure rules that use node attributes to affect where resources are placed.

⁠3.3.1. Setting and querying node attributes

Node attributes can be set and queried using the crm_attribute and attrd_updater commands, so that the user does not have to deal with XML configuration directly.

Here is an example of what XML configuration would be generated if an administrator ran this command:

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Example 3.2. Result of using crm_attribute to specify which kernel pcmk-1 is running

# crm_attribute --type nodes --node pcmk-1 --name kernel --update $(uname -r)

<node id="1" uname="pcmk-1">
   <instance_attributes id="nodes-1-attributes">
     <nvpair id="nodes-1-kernel" name="kernel" value="3.10.0-862.14.4.el7.x86_64"/>
   </instance_attributes>
</node>

To read back the value that was just set:

# crm_attribute --type nodes --node pcmk-1 --name kernel --query
scope=nodes  name=kernel value=3.10.0-862.14.4.el7.x86_64

By specifying --type nodes the admin tells the cluster that this attribute is persistent across reboots. There are also transient attributes which are kept in the status section and are "forgotten" whenever the node leaves the cluster. Administrators can use this section by specifying --type status.