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== Defining a Cluster Node ==
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Each node in the cluster will have an entry in the nodes section
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containing its UUID, uname, and type.
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.Example Heartbeat cluster node entry
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<node id="1186dc9a-324d-425a-966e-d757e693dc86" uname="pcmk-1" type="normal"/>
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.Example Corosync cluster node entry
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<node id="101" uname="pcmk-1" type="normal"/>
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In normal circumstances, the admin should let the cluster populate
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this information automatically from the communications and membership
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data. However for Heartbeat, one can use the `crm_uuid` tool
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to read an existing UUID or define a value before the cluster starts.
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== Where Pacemaker Gets the Node Name ==
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Traditionally, Pacemaker required nodes to be referred to by the value
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returned by `uname -n`. This can be problematic for services that
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require the `uname -n` to be a specific value (ie. for a licence
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Since version 2.0.0 of Pacemaker, this requirement has been relaxed
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for clusters using Corosync 2.0 or later. The name Pacemaker uses is:
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. The value stored in 'corosync.conf' under +ring0_addr+ in the +nodelist+, if it does not contain an IP address; otherwise
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. The value stored in 'corosync.conf' under +name+ in the +nodelist+; otherwise
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. The value of `uname -n`
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Pacemaker provides the `crm_node -n` command which displays the name
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used by a running cluster.
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If a Corosync nodelist is used, `crm_node --name-for-id $number` is also
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available to display the name used by the node with the corosync
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+nodeid+ of '$number', for example: `crm_node --name-for-id 2`.
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== Describing a Cluster Node ==
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indexterm:[Node,attribute]
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Beyond the basic definition of a node the administrator can also
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describe the node's attributes, such as how much RAM, disk, what OS or
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kernel version it has, perhaps even its physical location. This
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information can then be used by the cluster when deciding where to
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place resources. For more information on the use of node attributes,
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Node attributes can be specified ahead of time or populated later,
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when the cluster is running, using `crm_attribute`.
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Below is what the node's definition would look like if the admin ran the command:
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.The result of using crm_attribute to specify which kernel pcmk-1 is running
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# crm_attribute --type nodes --node-uname pcmk-1 --attr-name kernel --attr-value `uname -r`
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<node uname="pcmk-1" type="normal" id="101">
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<instance_attributes id="nodes-101">
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<nvpair id="kernel-101" name="kernel" value="2.6.16.46-0.4-default"/>
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</instance_attributes>
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A simpler way to determine the current value of an attribute is to use `crm_attribute` command again:
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# crm_attribute --type nodes --node-uname pcmk-1 --attr-name kernel --get-value
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By specifying `--type nodes` the admin tells the cluster that this
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attribute is persistent. There are also transient attributes which
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are kept in the status section which are "forgotten" whenever the node
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rejoins the cluster. The cluster uses this area to store a record of
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how many times a resource has failed on that node but administrators
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can also read and write to this section by specifying `--type status`.
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=== Adding a New Corosync Node ===
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indexterm:[Corosync,Add Cluster Node]
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indexterm:[Add Cluster Node,Corosync]
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Adding a new node is as simple as installing Corosync and Pacemaker,
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and copying '/etc/corosync/corosync.conf' and '/etc/corosync/authkey' (if
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it exists) from an existing node. You may need to modify the
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+mcastaddr+ option to match the new node's IP address.
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If a log message containing "Invalid digest" appears from Corosync,
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the keys are not consistent between the machines.
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=== Removing a Corosync Node ===
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indexterm:[Corosync,Remove Cluster Node]
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indexterm:[Remove Cluster Node,Corosync]
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Because the messaging and membership layers are the authoritative
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source for cluster nodes, deleting them from the CIB is not a reliable
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solution. First one must arrange for corosync to forget about the
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node (_pcmk-1_ in the example below).
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On the host to be removed:
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. Stop the cluster: `/etc/init.d/corosync stop`
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Next, from one of the remaining active cluster nodes:
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. Tell Pacemaker to forget about the removed host:
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This includes deleting the node from the CIB
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This proceedure only works for versions after 1.1.8
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=== Replacing a Corosync Node ===
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indexterm:[Corosync,Replace Cluster Node]
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indexterm:[Replace Cluster Node,Corosync]
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The five-step guide to replacing an existing cluster node:
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. Make sure the old node is completely stopped
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. Give the new machine the same hostname and IP address as the old one
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. Install the cluster software :-)
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. Copy '/etc/corosync/corosync.conf' and '/etc/corosync/authkey' (if it exists) to the new node
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. Start the new cluster node
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If a log message containing "Invalid digest" appears from Corosync,
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the keys are not consistent between the machines.
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=== Adding a New CMAN Node ===
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indexterm:[CMAN,Add Cluster Node]
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indexterm:[Add Cluster Node,CMAN]
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=== Removing a CMAN Node ===
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indexterm:[CMAN,Remove Cluster Node]
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indexterm:[Remove Cluster Node,CMAN]
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=== Adding a New Heartbeat Node ===
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indexterm:[Heartbeat,Add Cluster Node]
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indexterm:[Add Cluster Node,Heartbeat]
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Provided you specified +autojoin any+ in 'ha.cf', adding a new node is
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as simple as installing heartbeat and copying 'ha.cf' and 'authkeys'
170
from an existing node.
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If you don't want to use +autojoin+, then after setting up 'ha.cf' and
173
'authkeys', you must use `hb_addnode` before starting the new node.
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=== Removing a Heartbeat Node ===
177
indexterm:[Heartbeat,Remove Cluster Node]
178
indexterm:[Remove Cluster Node,Heartbeat]
180
Because the messaging and membership layers are the authoritative
181
source for cluster nodes, deleting them from the CIB is not a reliable
184
First one must arrange for Heartbeat to forget about the node (pcmk-1
185
in the example below).
187
On the host to be removed:
189
. Stop the cluster: `/etc/init.d/corosync stop`
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Next, from one of the remaining active cluster nodes:
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. Tell Heartbeat the node should be removed
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. Tell Pacemaker to forget about the removed host:
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This proceedure only works for versions after 1.1.8
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=== Replacing a Heartbeat Node ===
210
indexterm:[Heartbeat,Replace Cluster Node]
211
indexterm:[Replace Cluster Node,Heartbeat]
212
The seven-step guide to replacing an existing cluster node:
214
. Make sure the old node is completely stopped
215
. Give the new machine the same hostname as the old one
216
. Go to an active cluster node and look up the UUID for the old node in '/var/lib/heartbeat/hostcache'
217
. Install the cluster software
218
. Copy 'ha.cf' and 'authkeys' to the new node
219
. On the new node, populate it's UUID using `crm_uuid -w` and the UUID from step 2
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. Start the new cluster node
added
removed
doc/Pacemaker_Explained/en-US/Ch-Nodes.txt
