Sunday, July 17, 2011

Changing IP and VLAN on host - no VM downtime

It is possible to change the service console (COS) IP and VLAN id for hosts in a cluster without having VM downtime (see this post for changing hostname). The trick is to change the COS IP first on all hosts and then wait with the changing of the vMotion IP until all COS IP's have been changed. This way, you will be able to put the hosts into maintenance mode one by one and vMotion will still work with the old IP even though COS IP's will differ in range and VLAN id.

NB. It may be neccesary to disable HA for the cluster before you begin as the HA agent will not be able to configure on the hosts when IP's don't match for all hosts.

  1. Enter maintenance mode
  2. Update the DNS entry on the DNS server
  3. Log on to the vCenter server and flush the DNS: ipconfig /flushdns
  4. Go to ILO, DRAC or something similar for the host (you will loose remote network connection when changing the IP) and change the IP (use this KB article for inspiration): [root@server root]# esxcfg-vswif -i a.b.c.d -n w.x.y.z vswif0 , where a.b.c.d is the IP address and w.x.y.z is the subnet mask.
  5. Change the VLAN id (in this case VLAN 12): esxcfg-vswitch -v 12 -p 'Service Console' vSwitch0
  6. Change gateway: nano /etc/sysconfig/network
  7. Change DNS servers: nano /etc/resolv.conf
  8. Restart network: service network restart
  9. Ensure that gateway can be pinged
  10. Update the NTP server from the vSphere client if needed.
  11. Continue the process with next host in the cluster
When all COS IP's have been changed, go to the vSphere client and change all vMotion IP addresses and VLAN id's. This will not require any downtime. And then test that vMotion works.

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