Friday 6 November 2009

High Availability for IAG

After four hours on the train today, I spent a fair chunk of today configuring a pair of Celestix Load Balancers for an IAG deployment.

The only way to create IAG in a highly available configuration, is to put the IAG solution behind a front end load balancer. A common question I get asked is why do I recommend a pair of load balancers... well why would specify a solution with multiple application servers, only to place them behind a single load balancer and risk moving your single of failure from the application server, to the load balancing solution.

There are some simple instructions on how to configure the Celestix Load Balancers (CLB) and well documented in the manuals, but here are some headline points when configuring the solution for Direct Server Return (DSR), where the load balancer coming into the IAG solution, but outbound (as the name suggests) the IAG solution will go directly back to the client, rather than through the load balancer.
  1. Configure the IAG external IP address to the be the virtual server IP address
  2. Ensure DSR is selected in the advanced settings
  3. Under the Healthcheck option for the target, ensure PING is off, but check TCPOpen ais enabled for 443,2,10
  4. Ensure all IP addresses are unique, including gateways, servers, engines, etc.
  5. Create an ISA rule to allow access from the CLB range to the Local Host, for port 443.
  6. Create loopback adapters for the WSA appliance, ensuring that there is no gateway, and within advanced ssettings, the Interface Metric is set to 254
  7. Ensure VRRP is enable, where both appliances have the same VRID, ensure the Master has a priority of 1 and the backup of 254, on a different network
  8. Ensure the local host files that the server name points to the VIP

I had a pretty unique situation today, where four portals were configured on two IAG appliances, with virtual IPs and load balancers.

We ended up using 14 external IP addresses, VIP for each portal (4 external IPs), an external IP for each portal on each appliance (8 external IPs), and a unique IP for each load balancer (2 external IPs). It's very rare to have this many real IPs to play with, but the same principle would apply, if these IPs were internal ones behind a NAT'ing device, which would only have required 4 external IPs (one for each portal)

Ensure you understand the customer requirements and follow the manual.

Good luck with maaking your IAG solutions highly available! :)

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