[ASM] : "Request length exceeds defined buffer size " - How to increase the limit ?

I am not aware of an option that does this for a specific URL.
My suggestion is to change the long_request_buffer_size as described in K01235989 and activate an iRule/LTM policy that blocks larger requests on all other URL and virtual servers (if needed).

Alternatively you can bypass the ASM for the path completely (K22021244)

Hi Blue_whale​,

to my knowledge you cannot extend the limit per URL, but you can unblock a request which triggers this violation for a specific URL with an iRule:

when ASM_REQUEST_DONE {
    if {[ASM::violation names] contains "VIOLATION_REQUEST_TOO_LONG" and [string tolower [HTTP::uri]] starts_with "/stock.option"} {
        ASM::unblock        
    } 
}

Cheers

Daniel

Hello Blue_whale​  

Via system variables you could do it. 
In my case environment I had to increase it.

-ASCapi

For some violations using Microservices is great to stop the violation just for specific fqdn hostname and URL. Only method for microservices can't be selected as this may need Request For Enhancement .

https://techdocs.f5.com/en-us/bigip-14-1-0/big-ip-asm-implementations-14-1-0/working-with-bigip-security-policy-microservices.html

In my opinion, the best thing to do is to disable blocking for this.