A coworker brought an interesting problem to me the other day. He wanted to move a serverfarm from one server VLAN to another without taking an outage. Since I didn’t want to have to come into the office late at night to do work, I decided to see what we could do.
It turned out to be pretty easy. We tend to think of CSM VLANs as pairs — you have the client VLAN for the web servers where the vserver sits and the server VLAN where the serverfarm sits. The CSM doesn’t know about these relationships; all it cares about is whether the servers are in a server VLAN, and we can use that to our advantage here.
Here’s a snippet of what the original config looked like (not really since I’m not telling you how my company’s network is set up). The original serverfarm included a serverfarm called SFARM-ORIG that included 192.168.0.10. That farm is used by the vserver VSERV-ORIG that listens to 188.8.131.52 on HTTP. The probe is in there, too.
123456789101112131415 probe HTTP tcpport 80!serverfarm SFARM-ORIGreal 192.168.0.101inservicereal 192.168.0.102inserviceprobe HTTP!vserver VSERV-ORIGvirtual 184.108.40.206 tcp httpvlan 100serverfarm SFARM-ORIGinservice
To make the move, we start by creating a new vserver and serverfarm that contains all the IPs invovled — both the original IPs that are already in service as well as the new IPs to which the servers will migrate. The new vserver listens for 220.127.116.11. In this case, we’re moving the servers to 10.10.1.10.
12345678910111213141516 serverfarm SFARM-NEWreal 192.168.0.101inservicereal 192.168.0.102inservicereal 10.10.1.101inservicereal 10.10.1.102inserviceprobe HTTP!vserver VSERV-NEWvirtual 18.104.22.168 tcp httpvlan 200serverfarm SFARM-NEWinservice
When you first drop in the config, the original RIPs should come up as operational, and the new ones should fail since they don’t exist yet (duh!). When everyone’s ready, you then move the service over to the new VIP and run off of that for a while to make sure everything’s working as expected. When all the parties involved are happy, you can then start moving over the servers one at a time. The probe should fail out a server pretty quickly, then, when the server is reconfigured and put on the right VLAN, the CSM should eventually see the new RIP come up and put it back in the available server pool for the farm.
Configured like that, you can move the servers whenever you would like, and the CSM will automatically detect the changes and act accordingly. You just have to remember to remove the old IPs out of the serverfarm when a server moves.
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