VIP Selecting a Pool Member Based on Dependancy

Folks,

 

I have attached a diagram to explain what I'm trying to achieve. In summary, I'd like to configure a VIP listening on HTTP with a pool containing two pool members. Each pool member is located in a different data centre. The availability of the pool member is based on its health along with it's upstream server. The health check will be different for each tier.

 

To summarise the architecture:

 

• The pool contains two pool members: dc1srv1 and dc2srv1
• The VIP should only send traffic to a pool member if its upstream server is also alive

 

I've been through a number of iterations on paper. From a conventional method (through the GUI) I can't just add four health checks to a pool because the truth table wouldn't work. I can't nest health checks because it isn't possible.

 

I'm thinking this is going to require something like:

 

• Each node will be assigned a http-based health check appropriate for it's tier
• The pool will contain two pool members; dc1srv1 and dc2srv1
• The VIP will listen on port 80
• The smarts will be an iRule that when a client connects the script will assign traffic to a pool member only if it and it's upstream tier are both passing their health checks

Is what I'm asking for based on reality? Is the iRule necessary? Have I missed anything?

 

Thank you for your help.

 

Timothy