Each cluster node will have an entry in the nodes section containing at least an ID and a name. A cluster node’s ID is defined by the cluster layer (Corosync).
Example Corosync cluster node entry
<node id="101" uname="pcmk-1"/>
In normal circumstances, the admin should let the cluster populate this information automatically from the cluster layer.
The name that Pacemaker uses for a node in the configuration does not have to be the same as its local hostname. Pacemaker uses the following for a Corosync node’s name, in order of most preferred first:
If the cluster is running, the crm_node -n command will display the local node’s name as used by the cluster.
If a Corosync nodelist is used, crm_node --name-for-id with a Corosync node ID will display the name used by the node with the given Corosync nodeid, for example:
crm_node --name-for-id 2
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.
Node attributes come in two types, permanent and transient. Permanent node attributes are kept within the node entry, and keep their values even if the cluster restarts on a node. Transient node attributes are kept in the CIB’s status section, and go away when the cluster stops on the 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.
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 command to set a permanent node attribute, and the XML configuration that would be generated:
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
The --type nodes indicates that this is a permanent node attribute; --type status would indicate a transient node attribute.
Certain node attributes have special meaning to the cluster.
Node attribute names beginning with # are considered reserved for these special attributes. Some special attributes do not start with #, for historical reasons.
Certain special attributes are set automatically by the cluster, should never be modified directly, and can be used only within Rules; these are listed under built-in node attributes.
For true/false values, the cluster considers a value of “1”, “y”, “yes”, “on”, or “true” (case-insensitively) to be true, “0”, “n”, “no”, “off”, “false”, or unset to be false, and anything else to be an error.
| Name | Description |
|---|---|
| fail-count-* | Attributes whose names start with fail-count- are managed by the cluster to track how many times particular resource operations have failed on this node. These should be queried and cleared via the crm_failcount or crm_resource --cleanup commands rather than directly. |
| last-failure-* | Attributes whose names start with last-failure- are managed by the cluster to track when particular resource operations have most recently failed on this node. These should be cleared via the crm_failcount or crm_resource --cleanup commands rather than directly. |
| maintenance | Similar to the maintenance-mode cluster option, but for a single node. If true, resources will not be started or stopped on the node, resources and individual clone instances running on the node will become unmanaged, and any recurring operations for those will be cancelled. Warning: Restarting pacemaker on a node that is in single-node maintenance mode will likely lead to undesirable effects. If maintenance is set as a transient attribute, it will be erased when Pacemaker is stopped, which will immediately take the node out of maintenance mode and likely get it fenced. Even if permanent, if Pacemaker is restarted, any resources active on the node will have their local history erased when the node rejoins, so the cluster will no longer consider them running on the node and thus will consider them managed again, leading them to be started elsewhere. This behavior might be improved in a future release. |
| probe_complete | This is managed by the cluster to detect when nodes need to be reprobed, and should never be used directly. |
| resource-discovery-enabled | If the node is a remote node, fencing is enabled, and this attribute is explicitly set to false (unset means true in this case), resource discovery (probes) will not be done on this node. This is highly discouraged; the resource-discovery location constraint property is preferred for this purpose. |
| shutdown | This is managed by the cluster to orchestrate the shutdown of a node, and should never be used directly. |
| site-name | If set, this will be used as the value of the #site-name node attribute used in rules. (If not set, the value of the cluster-name cluster option will be used as #site-name instead.) |
| standby | If true, the node is in standby mode. This is typically set and queried via the crm_standby command rather than directly. |
| terminate | If the value is true or begins with any nonzero number, the node will be fenced. This is typically set by tools rather than directly. |
| #digests-* | Attributes whose names start with #digests- are managed by the cluster to detect when Unfencing needs to be redone, and should never be used directly. |
| #node-unfenced | When the node was last unfenced (as seconds since the epoch). This is managed by the cluster and should never be used directly. |