Introducing the load-balancing feature with Pacemaker.

Pacemaker allows you to perform load-balancing mecanism thanks to the IPaddr2 resource agent. The point here is to set a virtual IP and make it available in an active/active mode with the help of pacemaker clone.

$ sudo crm configure primitive p_vip ocf:heartbeat:IPaddr2 \

params ip="172.17.1.100" cidr_netmask="24" nic="eth0" clusterip_hash="sourceip-sourceport" \

op start interval="0s" timeout="60s" \

op monitor interval="5s" timeout="20s" \

op stop interval="0s" timeout="60s" \

What about this clusterip_hash parameter? Specify the hashing algorithm used for the Cluster IP functionality. This parameter is optional by default and the default value is sourceip-sourceport. The CLUSTERIP target is used to create simple clusters of nodes answering to the same IP and MAC address in a round robin fashion.

Possible values:

• sourceip
• sourceip-sourceport
• sourceip-sourceport-destport

This will create the following IPTABLES rule:

Chain INPUT (policy ACCEPT 27879 packets, 6604K bytes)

pkts bytes target prot opt in out source destination

0 0 CLUSTERIP all -- eth0 any anywhere 172.17.1.100 CLUSTERIP hashmode=sourceip clustermac=61:0E:45:64:50:A7 total_nodes=2 local_node=2 hash_init=0

The clustermac is automatically generated by the RA. If you want to learn more about the CLUSTERIP target read that link.

Set up your clone:

$ sudo crm configure clone clo_vip p_vip \

meta master-max="2" master-node-max="2" clone-max="2" clone-node-max="1" notify="true" interleave="true"

If you want to learn more about the interleave parameter look at the Hastexo article.

Test it, for this purpose you will need to ping the VIP from several client sources and each pacemaker node where the clone runs, execute the following command:

$ sudo tcpdump -i eth0 ‘icmp[icmptype] = icmp-echoreply‘

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode

listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes

02:25:23.612684 IP 172.17.1.100 > 172.17.1.7: ICMP echo reply, id 1569, seq 1, length 64

02:25:24.611475 IP 172.17.1.100 > 172.17.1.7: ICMP echo reply, id 1569, seq 2, length 64

02:25:25.610417 IP 172.17.1.100 > 172.17.1.7: ICMP echo reply, id 1569, seq 3, length 64

Sometime this solution could be useful but at the end it doesn’t replace a ‘real’ load-balancer like LVS.

Interleaving in Pacemaker clones

Ever wonder what meta interleave really means in a Pacemaker clone definition? We‘ll explain.

The interleave meta attribute is only valid on Pacemaker clone definitions – and their extended version of sorts, master/slave sets. It‘s not available on primitives and groups. Clones are often used in configurations involving cluster filesystems, such as GFS2 (here‘s an example).

Consider the following example (primitive definitions omitted to keep this short):

clone cl_foo p_foo meta interleave=false

clone cl_bar p_bar meta interleave=false

order o_foo_before_bar inf: cl_foo cl_bar

What this means is for the order constraint to be fulfilled, all instances of cl_foo must start before any instance of cl_bar can. Often, that‘s not what you want.

In contrast, consider this:

clone cl_foo p_foo meta interleave=true

clone cl_bar p_bar meta interleave=true

order o_foo_before_bar inf: cl_foo cl_bar

Here, for each node, as soon as the local instance of cl_foo has started, the corresponding local instance of cl_bar can, too. This is what‘s usually desired – when in doubt, allow interleaving.

One thing that often throws people is that interleaving only works when Pacemaker is configured to run the same number of instances of two clones on the same node. Thus,

clone cl_foo p_foo\

meta interleave=true \

globally-unique=true clone-node-max=2

clone cl_bar p_bar meta interleave=false

order o_foo_before_bar inf: cl_foo cl_bar

... won‘t work, as Pacemaker is allowed to run 2 instances of cl_foo on the same node, but only one of cl_bar (the default for clone-node-max is 1).

Also, globally-unique=true is a requirement for any clone-node-max>1 – which means that interleaving between a globally-unique and a not globally-unique clone is also not supported.