= Creating an Active/Passive Cluster =

== Exploring the Existing Configuration ==

When Pacemaker starts up, it automatically records the number and details
of the nodes in the cluster as well as which stack is being used and the
version of Pacemaker being used. 

This is what the base configuration should look like.

[source,Bash]
----
# crm configure show
node pcmk-1
node pcmk-2
property $id="cib-bootstrap-options" \
    dc-version="1.1.5-bdd89e69ba545404d02445be1f3d72e6a203ba2f" \
    cluster-infrastructure="openais" \
    expected-quorum-votes="2"
----

For those that are not of afraid of XML, you can see the raw
configuration by appending "xml" to the previous command.

.The last XML you'll see in this document
[source,Bash]
----
# crm configure show xml
<?xml version="1.0" ?>
<cib admin_epoch="0" crm_feature_set="3.0.1" dc-uuid="pcmk-1" epoch="13" have-quorum="1" num_updates="7" validate-with="pacemaker-1.0">
 <configuration>
  <crm_config>
   <cluster_property_set id="cib-bootstrap-options">
    <nvpair id="cib-bootstrap-options-dc-version" name="dc-version" value="1.1.5-bdd89e69ba545404d02445be1f3d72e6a203ba2f"/>
    <nvpair id="cib-bootstrap-options-cluster-infrastructure" name="cluster-infrastructure" value="openais"/>
    <nvpair id="cib-bootstrap-options-expected-quorum-votes" name="expected-quorum-votes" value="2"/>
   </cluster_property_set>
  </crm_config>
  <rsc_defaults/>
  <op_defaults/>
  <nodes>
   <node id="pcmk-1" type="normal" uname="pcmk-1"/>
   <node id="pcmk-2" type="normal" uname="pcmk-2"/>
  </nodes>
  <resources/>
  <constraints/>
 </configuration>
</cib>
----

Before we make any changes, its a good idea to check the validity of
the configuration.

[source,Bash]
----
# crm_verify -L
crm_verify[2195]: 2009/08/27_16:57:12 ERROR: unpack_resources: Resource start-up disabled since no STONITH resources have been defined
crm_verify[2195]: 2009/08/27_16:57:12 ERROR: unpack_resources: Either configure some or disable STONITH with the stonith-enabled option
crm_verify[2195]: 2009/08/27_16:57:12 ERROR: unpack_resources: NOTE: Clusters with shared data need STONITH to ensure data integrity
Errors found during check: config not valid -V may provide more details
#
----

As you can see, the tool has found some errors.

In order to guarantee the safety of your data
footnote:[If the data is corrupt, there is little point in continuing to make it available]
, Pacemaker ships with STONITH
footnote:[A common node fencing mechanism. Used to ensure data integrity by powering off "bad" nodes]
enabled.  However it also knows when no STONITH configuration has been
supplied and reports this as a problem (since the cluster would not be
able to make progress if a situation requiring node fencing arose).

For now, we will disable this feature and configure it later in the
Configuring STONITH section. It is important to note that the use of
STONITH is highly encouraged, turning it off tells the cluster to
simply pretend that failed nodes are safely powered off. Some vendors
will even refuse to support clusters that have it disabled. 

To disable STONITH, we set the stonith-enabled cluster option to
false.

[source,Bash]
----
# crm configure property stonith-enabled=false
# crm_verify -L
----

With the new cluster option set, the configuration is now valid.

[WARNING]
=========

The use of stonith-enabled=false is completely inappropriate for a
production cluster. We use it here to defer the discussion of its
configuration which can differ widely from one installation to the
next.  See  <<_what_is_stonith>> for information on why STONITH is important
and details on how to configure it.

=========

== Adding a Resource ==

The first thing we should do is configure an IP address. Regardless of
where the cluster service(s) are running, we need a consistent address
to contact them on. Here I will choose and add 192.168.122.101 as the
floating address, give it the imaginative name ClusterIP and tell the
cluster to check that its running every 30 seconds.


[IMPORTANT]
===========
The chosen address must not be one already associated with
a physical node
===========

[source,Bash]
----
# crm configure primitive ClusterIP ocf:heartbeat:IPaddr2 \
     params ip=192.168.122.101 cidr_netmask=32 \
     op monitor interval=30s
----

The other important piece of information here is ocf:heartbeat:IPaddr2.

This tells Pacemaker three things about the resource you want to
add. The first field, ocf, is the standard to which the resource
script conforms to and where to find it. The second field is specific
to OCF resources and tells the cluster which namespace to find the
resource script in, in this case heartbeat. The last field indicates
the name of the resource script.

To obtain a list of the available resource classes, run

[source,Bash]
----
# crm ra classesheartbeat
lsb ocf / heartbeat pacemakerstonith
----

To then find all the OCF resource agents provided by Pacemaker and
Heartbeat, run

[source,Bash]
----
# crm ra list ocf pacemaker
ClusterMon   Dummy     Stateful    SysInfo    SystemHealth  controld
ping      pingd     
# crm ra list ocf heartbeat
AoEtarget       AudibleAlarm      ClusterMon       Delay
Dummy         EvmsSCC        Evmsd         Filesystem
ICP          IPaddr         IPaddr2        IPsrcaddr
LVM          LinuxSCSI       MailTo         ManageRAID
ManageVE        Pure-FTPd       Raid1         Route
SAPDatabase      SAPInstance      SendArp        ServeRAID
SphinxSearchDaemon   Squid         Stateful        SysInfo
VIPArip        VirtualDomain     WAS          WAS6
WinPopup        Xen          Xinetd         anything
apache         db2          drbd          eDir88
iSCSILogicalUnit    iSCSITarget      ids          iscsi
ldirectord       mysql         mysql-proxy      nfsserver
oracle         oralsnr        pgsql         pingd
portblock       rsyncd         scsi2reservation    sfex
tomcat         vmware         
#
----

Now verify that the IP resource has been added and display the cluster's
status to see that it is now active.

[source,Bash]
----
# crm configure shownode pcmk-1
node pcmk-2primitive ClusterIP ocf:heartbeat:IPaddr2 \
    params ip="192.168.122.101" cidr_netmask="32" \
    op monitor interval="30s"
property $id="cib-bootstrap-options" \
    dc-version="1.1.5-bdd89e69ba545404d02445be1f3d72e6a203ba2f" \
    cluster-infrastructure="openais" \
    expected-quorum-votes="2" \
    stonith-enabled="false" \
# crm_mon
============
Last updated: Fri Aug 28 15:23:48 2009
Stack: openais
Current DC: pcmk-1 - partition with quorum
Version: 1.1.5-bdd89e69ba545404d02445be1f3d72e6a203ba2f
2 Nodes configured, 2 expected votes
1 Resources configured.
============

Online: [ pcmk-1 pcmk-2 ]
ClusterIP (ocf::heartbeat:IPaddr): Started pcmk-1
----

== Perform a Failover ==

Being a high-availability cluster, we should test failover of our new
resource before moving on. 

First, find the node on which the IP address is running.

[source,Bash]
----
# crm resource status ClusterIP
resource ClusterIP is running on: pcmk-1
#
----

Shut down Pacemaker and Corosync on that machine.

[source,Bash]
----
# ssh pcmk-1 -- /etc/init.d/pacemaker stop
Signaling Pacemaker Cluster Manager to terminate: [ OK ]
Waiting for cluster services to unload:. [ OK ]
# ssh pcmk-1 -- /etc/init.d/corosync stop
Stopping Corosync Cluster Engine (corosync): [ OK ]
Waiting for services to unload: [ OK ]
#
----

Once Corosync is no longer running, go to the other node and check the
cluster status with crm_mon.

[source,Bash]
----
# crm_mon
============
Last updated: Fri Aug 28 15:27:35 2009
Stack: openais
Current DC: pcmk-2 - partition WITHOUT quorum
Version: 1.1.5-bdd89e69ba545404d02445be1f3d72e6a203ba2f
2 Nodes configured, 2 expected votes
1 Resources configured.
============

Online: [ pcmk-2 ]OFFLINE: [ pcmk-1 ]
----

There are three things to notice about the cluster's current
state. The first is that, as expected, pcmk-1 is now offline. However
we can also see that ClusterIP isn't running anywhere!


=== Quorum and Two-Node Clusters ===

This is because the cluster no longer has quorum, as can be seen by
the text "partition WITHOUT quorum" (emphasised green) in the output
above.  In order to reduce the possibility of data corruption,
Pacemaker's default behavior is to stop all resources if the cluster
does not have quorum.

A cluster is said to have quorum when more than half the known or
expected nodes are online, or for the mathematically inclined,
whenever the following equation is true:

....
total_nodes < 2 * active_nodes
....

Therefore a two-node cluster only has quorum when both nodes are
running, which is no longer the case for our cluster. This would
normally make the creation of a two-node cluster pointless
footnote:[Actually some would argue that two-node clusters are always pointless, but that is an argument for another time]
, however it is possible to control how Pacemaker behaves when quorum
is lost. In particular, we can tell the cluster to simply ignore
quorum altogether.

[source,Bash]
----
# crm configure property no-quorum-policy=ignore
# crm configure show
node pcmk-1
node pcmk-2
primitive ClusterIP ocf:heartbeat:IPaddr2 \
    params ip="192.168.122.101" cidr_netmask="32" \
    op monitor interval="30s"
property $id="cib-bootstrap-options" \
    dc-version="1.1.5-bdd89e69ba545404d02445be1f3d72e6a203ba2f" \
    cluster-infrastructure="openais" \
    expected-quorum-votes="2" \
    stonith-enabled="false" \
    no-quorum-policy="ignore"
----

After a few moments, the cluster will start the IP address on the
remaining node. Note that the cluster still does not have quorum.

[source,Bash]
----
# crm_mon
============
Last updated: Fri Aug 28 15:30:18 2009
Stack: openais
Current DC: pcmk-2 - partition WITHOUT quorum
Version: 1.1.5-bdd89e69ba545404d02445be1f3d72e6a203ba2f
2 Nodes configured, 2 expected votes
1 Resources configured.
============
Online: [ pcmk-2 ]
OFFLINE: [ pcmk-1 ]
ClusterIP (ocf::heartbeat:IPaddr): Started pcmk-2
----

Now simulate node recovery by restarting the cluster stack on pcmk-1 and
check the cluster's status.

[source,Bash]
----
# /etc/init.d/corosync start
Starting Corosync Cluster Engine (corosync): [ OK ]      
# /etc/init.d/pacemaker start
Starting Pacemaker Cluster Manager: [ OK ]# crm_mon
============
Last updated: Fri Aug 28 15:32:13 2009
Stack: openais
Current DC: pcmk-2 - partition with quorum
Version: 1.1.5-bdd89e69ba545404d02445be1f3d72e6a203ba2f
2 Nodes configured, 2 expected votes
1 Resources configured.
============
Online: [ pcmk-1 pcmk-2 ]

ClusterIP    (ocf::heartbeat:IPaddr):    Started pcmk-1
----

Here we see something that some may consider surprising, the IP is back
running at its original location!


=== Prevent Resources from Moving after Recovery ===

In some circumstances, it is highly desirable to prevent healthy
resources from being moved around the cluster. Moving resources almost
always requires a period of downtime. For complex services like Oracle
databases, this period can be quite long.

To address this, Pacemaker has the concept of resource stickiness
which controls how much a service prefers to stay running where it
is. You may like to think of it as the "cost" of any downtime. By
default, Pacemaker assumes there is zero cost associated with moving
resources and will do so to achieve "optimal"
footnote:[It should be noted that Pacemaker's definition of
optimal may not always agree with that of a human's. The order in which
Pacemaker processes lists of resources and nodes creates implicit
preferences in situations where the administrator has not explicitly
specified them]
resource placement. We can specify a different stickiness for every
resource, but it is often sufficient to change the default.

[source,Bash]
----
# crm configure rsc_defaults resource-stickiness=100
# crm configure show
node pcmk-1
node pcmk-2
primitive ClusterIP ocf:heartbeat:IPaddr2 \
    params ip="192.168.122.101" cidr_netmask="32" \
    op monitor interval="30s"
property $id="cib-bootstrap-options" \
    dc-version="1.1.5-bdd89e69ba545404d02445be1f3d72e6a203ba2f" \
    cluster-infrastructure="openais" \
    expected-quorum-votes="2" \
    stonith-enabled="false" \
    no-quorum-policy="ignore"rsc_defaults $id="rsc-options" \
    resource-stickiness="100"
----

If we now retry the failover test, we see that as expected ClusterIP
still moves to pcmk-2 when pcmk-1 is taken offline.

[source,Bash]
----
# ssh pcmk-1 -- /etc/init.d/pacemaker stop
Signaling Pacemaker Cluster Manager to terminate:          [  OK  ]
Waiting for cluster services to unload:.                   [  OK  ]
# ssh pcmk-1 -- /etc/init.d/corosync stop
Stopping Corosync Cluster Engine (corosync):        [ OK ]
Waiting for services to unload:              [ OK ]
# ssh pcmk-2 -- crm_mon -1
============
Last updated: Fri Aug 28 15:39:38 2009
Stack: openais
Current DC: pcmk-2 - partition WITHOUT quorum
Version: 1.1.5-bdd89e69ba545404d02445be1f3d72e6a203ba2f
2 Nodes configured, 2 expected votes
1 Resources configured.
============

Online: [ pcmk-2 ]
OFFLINE: [ pcmk-1 ]
ClusterIP    (ocf::heartbeat:IPaddr):    Started pcmk-2
----

However when we bring pcmk-1 back online, ClusterIP now remains running
on pcmk-2.

[source,Bash]
----
# /etc/init.d/corosync start
Starting Corosync Cluster Engine (corosync): [ OK ]
# /etc/init.d/pacemaker start
Starting Pacemaker Cluster Manager: [ OK ]
# crm_mon
============
Last updated: Fri Aug 28 15:41:23 2009
Stack: openais
Current DC: pcmk-2 - partition with quorum
Version: 1.1.5-bdd89e69ba545404d02445be1f3d72e6a203ba2f
2 Nodes configured, 2 expected votes
1 Resources configured.
============

Online: [ pcmk-1 pcmk-2 ]
 
ClusterIP    (ocf::heartbeat:IPaddr):    Started pcmk-2
----