right, you have most of the options listed already. For completeness I am adding the external load balancer option:
- Built-in HA
- DNS Round Robin
- URLhash via proxy.pac (some more info on this one would be nice)
- external load balancing using load balancer
Hash routing provides:
- Scalability:No communication between proxy caches
- Deterministic fast routing at client and/or proxy
- even or heterogeneous load balance control
- No duplicated caching/efficient use of storage
- Robustness for failure/re-configuration
The basic idea is that once hash routing script is downloaded in Web browsers and if there are N proxies, then
- Hash routing script converts URL string into check sum (random hash number which is calculated uniquely from URL string)
- calculates hashing function i = Modulo(checksum(URL),N) for each requested URL.
- route client request to i-th proxy
(taken from http://www.pacfiles.com/images/SSP.htm)
For the built in one, you don't need a X-cable between the two instances it can communicate over a ususal network. As the HA is using broadcasts it is noteable that the two device must be in the same broadcast domain in order to let broadcasts appear on the single instances.
The VIP needs to be a free IP in the same subnet of the Webwashers, which can be set in each WW's UI, You obviously need to make sure you configure both with the same.