RHEL 7 – Pacemaker – Cluster Resource Agents Overview – Part 5

Resource agents plays an important role in cluster management.  Resource agents are multi-threaded processes that provides the logic to manage  the resources. Pacemaker has one agent per resource type. Resource type could be a File-system , IP address , databases, virtual-domain and more. Resource agent is responsible to monitor, start , stop,validate , migrate , promote and demote  the cluster resources whenever required. Most of the resource agents are compliant  to Open Cluster Framework (OCF) .  Let’s add one IP resource to the existing cluster and then we will get in to the detailed explanation of command options. 

 

1. Login to one of the Redhat Cluster (Pacemaker/corosync) cluster node as root user.

 

2. Check the cluster status .

[root@UA-HA ~]# pcs status
Cluster name: UABLR
Last updated: Mon Dec 28 13:06:01 2015          Last change: Sun Dec 27 23:59:59 2015 by root via cibadmin on UA-HA
Stack: corosync
Current DC: UA-HA (version 1.1.13-10.el7-44eb2dd) - partition with quorum
2 nodes and 0 resources configured

Online: [ UA-HA UA-HA2 ]

Full list of resources:


PCSD Status:
  UA-HA: Online
  UA-HA2: Online

Daemon Status:
  corosync: active/enabled
  pacemaker: active/enabled
  pcsd: active/enabled
[root@UA-HA ~]#

 

3. Add the IP which needs to be high-available (Clustered IP).

[root@UA-HA ~]# pcs resource create ClusterIP ocf:heartbeat:IPaddr2 ip=192.168.203.190 cidr_netmask=24 op monitor interval=30s
[root@UA-HA ~]#

ClusterIP – Resource Name(You can give any name)
ocf:heartbeat:IPaddr2 – Resource agent Name.

 

Resource Standard:

The first field (ocf in this case) is the standard to which the resource script conforms and where to find it.
To obtain a list of the available resource standards , use the following command.

[root@UA-HA ~]# pcs resource standards
ocf   - Open cluster Framework 
lsb   - Linux standard base (legacy init scripts)
service - Based on Linux "service" command. 
systemd  - systemd based service Management
stonith  - Fencing Resource standard. 
[root@UA-HA ~]#

 

Resource Provides:

The second field (heartbeat in this case) is standard-specific; for OCF resources, it tells the cluster which OCF namespace the resource script is in. To obtain a list of the available OCF resource providers, use the following command.

[root@UA-HA ~]# pcs resource providers
heartbeat
openstack
pacemaker
[root@UA-HA ~]#

 

What are the pre-built resource agents available in RHEL 7.2  ? 

The third field (IPaddr2 in this case) is the name of the resource script. To see all the resource agents available for a specific OCF provider (heartbeat) , use the following command.

[root@UA-HA ~]# pcs resource agents ocf:heartbeat
CTDB
Delay
Dummy
Filesystem
IPaddr
IPaddr2
IPsrcaddr
LVM
MailTo
Route
SendArp
Squid
VirtualDomain
Xinetd
apache
clvm
conntrackd
db2
dhcpd
docker
ethmonitor
exportfs
galera
iSCSILogicalUnit
iSCSITarget
iface-vlan
mysql
named
nfsnotify
nfsserver
nginx
oracle
oralsnr
pgsql
postfix
rabbitmq-cluster
redis
rsyncd
slapd
symlink
tomcat
[root@UA-HA ~]# pcs resource agents ocf:heartbeat |wc -l
41
[root@UA-HA ~]#

 

For Openstack , you have following resources agents.

[root@UA-HA ~]# pcs resource agents ocf:openstack
NovaCompute
NovaEvacuate
[root@UA-HA ~]#

 

Here is the list resource agents to manager the pacemaker components.

[root@UA-HA ~]# pcs resource agents ocf:pacemaker
ClusterMon
Dummy
HealthCPU
HealthSMART
Stateful
SysInfo
SystemHealth
controld
ping
pingd
remote
[root@UA-HA ~]#

 

4.Verify the resource status.

[root@UA-HA ~]# pcs status
Cluster name: UABLR
Last updated: Mon Dec 28 13:07:33 2015          Last change: Mon Dec 28 13:07:30 2015 by root via cibadmin on UA-HA
Stack: corosync
Current DC: UA-HA (version 1.1.13-10.el7-44eb2dd) - partition with quorum
2 nodes and 1 resource configured

Online: [ UA-HA UA-HA2 ]

Full list of resources:

 ClusterIP      (ocf::heartbeat:IPaddr2):       Started UA-HA

PCSD Status:
  UA-HA: Online
  UA-HA2: Online

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

 

As per the cluster status , IP resource is online on node “UA-HA” . Let’s verify from OS command line.

[root@UA-HA ~]# ip a |grep inet
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host
    inet 192.168.203.134/24 brd 192.168.203.255 scope global dynamic br0
    inet 192.168.203.190/24 brd 192.168.203.255 scope global secondary br0
    inet6 fe80::84ef:2eff:fee9:260a/64 scope link
    inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
[root@UA-HA ~]#
[root@UA-HA ~]# ping 192.168.203.190
PING 192.168.203.190 (192.168.203.190) 56(84) bytes of data.
64 bytes from 192.168.203.190: icmp_seq=1 ttl=64 time=0.084 ms
64 bytes from 192.168.203.190: icmp_seq=2 ttl=64 time=0.090 ms
64 bytes from 192.168.203.190: icmp_seq=3 ttl=64 time=0.121 ms
64 bytes from 192.168.203.190: icmp_seq=4 ttl=64 time=0.094 ms
^C
--- 192.168.203.190 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3006ms
rtt min/avg/max/mdev = 0.084/0.097/0.121/0.015 ms
[root@UA-HA ~]#

 

We can see that IP “192.168.203.190/24” is up & running. This IP will  automatically move from one node to another node if the system fails.