F5 FastL4 but need HTTP header insert

It is quite possible that the F5 BIG-IP box is trying to compress already-compressed data; I'm almost positive that it doesn't uncompress responses at all. The typical operation if compression is enabled is that the BIG-IP will not forward the Accept-Encoding header if the BIG-IP is taking responsibility for compressing content so that the server will not send compressed content; there is a compression profile option to override this (usually desirable) behavior.

 

 

If you care less about compression on the client side of the WAN, then you should disable it completely on the appropriate VIP(s) on the BIG-IP, and leave the compression to the remote load balancers; that would also send fewer bytes across the WAN link.

 

 

If you can't get packet traces, then you might want to look at iRules (particularly the HTTP_REQUEST_SEND and HTTP_RESPONSE events) to log the headers that the BIG-IP box is sending and receiving. If the BIG-IP is inappropriately compressing only some responses, then you might be able to tweak that behavior, either via compression profile options or additional iRules.

 

 

The real problem is that "just passing traffic" is fundamentally incompatible with "needing to insert HTTP headers". To insert a header, you need to know where to insert it, so you need to parse the HTTP data. Then, if you just pass the traffic, you also have to handle retransmissions, not to mention out-of-order packets. In short, "need to insert HTTP headers" really translates to "need to buffer and parse data and not just forward it".

 

 

If you only need to insert headers on the client requests, and not change server responses at all, then you might consider an nPath (aka Direct Server Return) configuration, though this may require changing your SNAT/NAT configuration.

 

 

I'm a little surprised that FastHTTP wasn't working for you, though, as it comes closest to "fastL4 + header insert", but you didn't mention how it didn't work. If it also showed the same bad latency, then that would almost certainly point to misconfiguration or other problems outside the BIG-IP. That said, FastHTTP is optimized for ideal conditions, which you may not find in your network.

 

 

Finally, F5 also sells products for optimizing HTTP across WAN links; you may want to look into those.