:compat-mode: legacy

= The Cluster Layer =

== Pacemaker and the Cluster Layer ==

Pacemaker utilizes an underlying cluster layer for two purposes:

* obtaining quorum

* messaging between nodes

Currently, only Corosync 2 and later is supported for this layer.

== Managing Nodes in a Corosync-Based Cluster ==

=== Adding a New Corosync Node ===

indexterm:[Corosync,Add Cluster Node]

indexterm:[Add Cluster Node,Corosync]

To add a new node:

. Install Corosync and Pacemaker on the new host.

. Copy +/etc/corosync/corosync.conf+ and +/etc/corosync/authkey+ (if it exists)

  from an existing node. You may need to modify the *mcastaddr* option to match

  the new node's IP address.

. Start the cluster software on the new host. If a log message containing

  "Invalid digest" appears from Corosync, the keys are not consistent between

  the machines.

=== Removing a Corosync Node ===

indexterm:[Corosync,Remove Cluster Node]

indexterm:[Remove Cluster Node,Corosync]

Because the messaging and membership layers are the authoritative

source for cluster nodes, deleting them from the CIB is not a complete

solution.  First, one must arrange for corosync to forget about the

node (*pcmk-1* in the example below).

. Stop the cluster on the host to be removed. How to do this will vary with

  your operating system and installed versions of cluster software, for example,

  `pcs cluster stop` if you are using pcs for cluster management.

. From one of the remaining active cluster nodes, tell Pacemaker to forget

  about the removed host, which will also delete the node from the CIB:

+

----

# crm_node -R pcmk-1

----

=== Replacing a Corosync Node ===

indexterm:[Corosync,Replace Cluster Node]

indexterm:[Replace Cluster Node,Corosync]

To replace an existing cluster node:

. Make sure the old node is completely stopped.

. Give the new machine the same hostname and IP address as the old one.

. Follow the procedure above for adding a node.