User talk:Gertp

Generic active/passive clusters

Configuring a cluster using corosync and heartbeat involves you having to write a start/stop and monitoring script for the service you are building the cluster for.

This script is very much like an "init.d" script, but you can't directly use an init.d script as heartbeat scripts use tri-state logic in stead of two-state logic. I.e., heartbeat controlled services are "running", "stopped" or "failed", whereas services controlled by init that fail are stopped and must be restarted. Heartbeat uses the third state "failed" as the trigger to migrate the service to another node in your services pool.

For a simple service consisting of one process, monitoring is easy and adaptation of an existing init.d script straighforward. Hint: use the sample

    /usr/lib/ocf/resource.d/heartbeat/Dummy

as a starting-point.

For services comprised of two or more processes, you'll have to loop over all processes, their pid and lock files to see whether processes are running and correspond to the lock and pid files. Assuming that all processes are well behaved and store pid and lock files in the standard locations.

BDII setup on active/passive failover cluster

The bdii services are not entirely well behaved. The pid files for the slapd daemon and bdii-update daemon are not in the same place (/var/run and /var/run/bdii/db, respectively), and the init.d script for the slapd daemon contains lots of cruft that shouldn't be part of an init script to begin with (such as initialization of the database).

Therefore the heartbeat script for the bdii service is a bit of kludge, remaining as close as possible to the init.d script it is derived from (so as to make adaptations doable as the init.d script evolves).

Click for the BDII heartbeat script.

Install the cluster engine & resource manager

You need to perform the installation on each cluster node.

Add the EPEL repo to /etc/yum.repos.d:

    # rpm -Uhv http://download.fedora.redhat.com/pub/epel/5/x86_64/epel-release-5-4.noarch.rpm 

Add the Clusterlabs repo to /etc/yum.repos.d:

    # wget -O /etc/yum.repos.d/pacemaker.repo http://clusterlabs.org/rpm/epel-5/clusterlabs.repo

Now have yum install the cluster engine and resource managers. This will install loads of dependencies:

    # yum -y install pacemaker

Configure the cluster engine

You need to do this on each cluster node.

First, copy the sample configuration for corosync to the default configuration:

    # cp /etc/corosync/corosync.conf{.example,}

Then, change te "bindnetaddr": the network that your cluster nodes are in:

    # perl -p -i -e 's|(bindnetaddr:).*|\1  194.171.X.0|' /etc/corosync/corosync.conf 

Also, append the following:

    # cat >>/etc/corosync/corosync.conf <<UFO
    aisexec {
            user: root
            group: root
    }
    service {
            name: pacemaker
            ver: 0
    }
    UFO

This tells corosync to run as root and to use the pacemaker resource manager.

Now start the cluster on one of the nodes:

   # /etc/init.d/corosync start

(For RHC[TE]'s that is:

   # service corosync start

). And check if there are any errors by inspecting the /var/log/corosync.log.

If there are no errors, start corosync on all other cluster nodes. Check that all nodes are running ok, you can now enable corosync to start at boottime on all nodes:

   # chkconfig corosync on

STONITH

STONITH is the acronym for Shoot The Other Node In The Head. It is used during a failover/recovery to take the failing node offline (or turning it off). At this moment we don't need it, so turn it off:

    # crm configure property stonith-enabled=false
    # crm_verify -L

Remember to do this on all nodes, again.

The HA service IP address

The service we want to offer using the cluster must be separate from the nodes own addresses, so it can migrate freely from one node to the other without users being aware of it. The service IP address must be in the same subnet as the cluster nodes are in.

Make sure that the DNS record fot the service IP address is a true A record. Once you have the IP address, assign the ClusterIP resource:

     # crm configure primitive ClusterIP ocf:heartbeat:IPaddr2 \
       params \
           ip=194.171.79.37 \
           cidr_netmask=32 \
       op monitor interval=10s