Failover web filtering?

Question

Two core sites (A & B), each site with 2x SG330 (hot standby) each with a 50mb fibre to the internet. Using multipath to balance between the two. 
 Using web proxy in transparent mode but would like to change to standard. 
 Currently all internet traffic goes to core site A (SG330 web proxy) and goes out 50/50 to internet and SITE B via dedicated uplink (leased line) 
 Now if we knock the SG330 off at SITE A, we can reroute internet traffic to site B SG330 and we can get it to go out via the UTM web proxy there (transparent) 
 Is it possible to change both UTM's to standard filtering instead of transparent? If all clients browsers (using standard) are pointing towards the UTM at site A, how can you get it to point to site B? Or am I stuck with transparent for this setup?

DouglasFoster · Answer

Standard mode does not fully displace Transparent Mode, because Standard Mode is essentially a suggestion to the client browser. There will always be traffic that does not notice or does not obey the suggestion. So use both modes. 
 You pose an interesting questions. There are several possible failure modes: 
 
 An ISP connection path fails, so UTM detects a failure to respond. 
 An ISP router fails, so UTM detects a down link 
 A UTM fails. 
 
 I think Standard Mode and Transparent Mode will behave identically in the first two cases. For those failures, you need to reconfigure external routing, either manually or automatically using OSPF or more likely BGP as appropriate. 
 In the case of the third failure, Transparent Mode requires that you reconfigure your internal routing, which may be challenging. Standard Mode requires only that the PROXY command be configured with options. this is an example: 
 return "PROXY utm1:8080; utm2:8080; DIRECT";