Start and Verify Cluster
------------------------

Start the Cluster
#################

Now that corosync is configured, it is time to start the cluster.
The command below will start corosync and pacemaker on both nodes
in the cluster.  If you are issuing the start command from a different
node than the one you ran the ``pcs host auth`` command on earlier, you
must authenticate on the current node you are logged into before you will
be allowed to start the cluster.

.. code-block:: none

    [root@pcmk-1 ~]# pcs cluster start --all
    pcmk-1: Starting Cluster...
    pcmk-2: Starting Cluster...

.. NOTE::

    An alternative to using the ``pcs cluster start --all`` command
    is to issue either of the below command sequences on each node in the
    cluster separately:

    .. code-block:: none

        # pcs cluster start
        Starting Cluster...

    or

    .. code-block:: none

        # systemctl start corosync.service
        # systemctl start pacemaker.service

.. IMPORTANT::

    In this example, we are not enabling the corosync and pacemaker services
    to start at boot. If a cluster node fails or is rebooted, you will need to run
    ``pcs cluster start <NODENAME>`` (or ``--all``) to start the cluster on it.
    While you could enable the services to start at boot, requiring a manual start
    of cluster services gives you the opportunity to do a post-mortem investigation
    of a node failure before returning it to the cluster.

Verify Corosync Installation
############################

First, use ``corosync-cfgtool`` to check whether cluster communication is happy:

.. code-block:: none

    [root@pcmk-1 ~]# corosync-cfgtool -s
    Printing link status.
    Local node ID 1
    LINK ID 0
	    addr	= 192.168.122.101
	    status:
		    nodeid  1:	localhost
		    nodeid  2:	connected

We can see here that everything appears normal with our fixed IP
address (not a 127.0.0.x loopback address) listed as the **addr**, and **localhost** and **connected** for the statuses of nodeid 1 and nodeid 2, respectively.

If you see something different, you might want to start by checking
the node's network, firewall and SELinux configurations.

Next, check the membership and quorum APIs:

.. code-block:: none

    [root@pcmk-1 ~]# corosync-cmapctl | grep members 
    runtime.members.1.config_version (u64) = 0
    runtime.members.1.ip (str) = r(0) ip(192.168.122.101) 
    runtime.members.1.join_count (u32) = 1
    runtime.members.1.status (str) = joined
    runtime.members.2.config_version (u64) = 0
    runtime.members.2.ip (str) = r(0) ip(192.168.122.102) 
    runtime.members.2.join_count (u32) = 1
    runtime.members.2.status (str) = joined
    [root@pcmk-1 ~]# pcs status corosync 

    Membership information
    ----------------------
        Nodeid      Votes Name
             1          1 pcmk-1 (local)
             2          1 pcmk-2

You should see both nodes have joined the cluster.

Verify Pacemaker Installation
#############################

Now that we have confirmed that Corosync is functional, we can check
the rest of the stack. Pacemaker has already been started, so verify
the necessary processes are running:

.. code-block:: none

    [root@pcmk-1 ~]# ps axf
      PID TTY      STAT   TIME COMMAND
        2 ?        S      0:00 [kthreadd]
    ...lots of processes...
    17121 ?        SLsl   0:01 /usr/sbin/corosync -f
    17133 ?        Ss     0:00 /usr/sbin/pacemakerd -f
    17134 ?        Ss     0:00  \_ /usr/libexec/pacemaker/pacemaker-based
    17135 ?        Ss     0:00  \_ /usr/libexec/pacemaker/pacemaker-fenced
    17136 ?        Ss     0:00  \_ /usr/libexec/pacemaker/pacemaker-execd
    17137 ?        Ss     0:00  \_ /usr/libexec/pacemaker/pacemaker-attrd
    17138 ?        Ss     0:00  \_ /usr/libexec/pacemaker/pacemaker-schedulerd
    17139 ?        Ss     0:00  \_ /usr/libexec/pacemaker/pacemaker-controld

If that looks OK, check the ``pcs status`` output:

.. code-block:: none

    [root@pcmk-1 ~]# pcs status
    Cluster name: mycluster
    
    WARNINGS:
    No stonith devices and stonith-enabled is not false
    
    Cluster Summary:
      * Stack: corosync
      * Current DC: pcmk-2 (version 2.0.5-4.el8-ba59be7122) - partition with quorum
      * Last updated: Wed Jan 20 07:54:02 2021
      * Last change:  Wed Jan 20 07:48:25 2021 by hacluster via crmd on pcmk-2
      * 2 nodes configured
      * 0 resource instances configured
    
    Node List:
      * Online: [ pcmk-1 pcmk-2 ]
    
    Full List of Resources:
      * No resources

    Daemon Status:
      corosync: active/disabled
      pacemaker: active/disabled
      pcsd: active/enabled

Finally, ensure there are no start-up errors from corosync or pacemaker (aside
from messages relating to not having STONITH configured, which are OK at this
point):

.. code-block:: none

    [root@pcmk-1 ~]# journalctl -b | grep -i error

.. NOTE::

    Other operating systems may report startup errors in other locations,
    for example ``/var/log/messages``.

Repeat these checks on the other node. The results should be the same.

Explore the Existing Configuration
##################################

For those who are not of afraid of XML, you can see the raw cluster
configuration and status by using the ``pcs cluster cib`` command.

.. topic:: The last XML you'll see in this document

    .. code-block:: none

        [root@pcmk-1 ~]# pcs cluster cib

    .. code-block:: xml

        <cib crm_feature_set="3.7.1" validate-with="pacemaker-3.6" epoch="5" num_updates="4" admin_epoch="0" cib-last-written="Tue Feb 16 16:20:57 2021" update-origin="pcmk-1" update-client="crmd" update-user="hacluster" have-quorum="1" dc-uuid="1">
          <configuration>
            <crm_config>
              <cluster_property_set id="cib-bootstrap-options">
                <nvpair id="cib-bootstrap-options-have-watchdog" name="have-watchdog" value="false"/>
                <nvpair id="cib-bootstrap-options-dc-version" name="dc-version" value="2.0.5-7.el8-ba59be7122"/>
                <nvpair id="cib-bootstrap-options-cluster-infrastructure" name="cluster-infrastructure" value="corosync"/>
                <nvpair id="cib-bootstrap-options-cluster-name" name="cluster-name" value="mycluster"/>
              </cluster_property_set>
            </crm_config>
            <nodes>
              <node id="1" uname="pcmk-1"/>
              <node id="2" uname="pcmk-2"/>
            </nodes>
            <resources/>
            <constraints/>
          </configuration>
          <status>
            <node_state id="2" uname="pcmk-2" in_ccm="true" crmd="online" crm-debug-origin="do_state_transition" join="member" expected="member">
              <lrm id="2">
                <lrm_resources/>
              </lrm>
            </node_state>
            <node_state id="1" uname="pcmk-1" in_ccm="true" crmd="online" crm-debug-origin="do_state_transition" join="member" expected="member">
              <lrm id="1">
                <lrm_resources/>
              </lrm>
            </node_state>
          </status>
        </cib>

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

.. code-block:: none

    [root@pcmk-1 ~]# crm_verify -L -V
       error: unpack_resources: Resource start-up disabled since no STONITH resources have been defined
       error: unpack_resources: Either configure some or disable STONITH with the stonith-enabled option
       error: unpack_resources: NOTE: Clusters with shared data need STONITH to ensure data integrity
    Errors found during check: config not valid

As you can see, the tool has found some errors. The cluster will not start any
resources until we configure STONITH.
