Fastly: Route n% of traffic based on a path param

Question

Have an interesting task when I don't want to have a full rollout of a new feature. I'd like to route only the percentage of traffic (based on a path parameter) to the new endpoint.

I'd like to calculate the percentage based on a 'specialPathParam': ourservice.com/one/'specialPathParam'/something .

So, if we want to route 50% to the new endpoint:

if there're 2 requests ourservice.com/one/'specialPathParamOne'/something ourservice.com/one/'specialPathParamTwo'/something ,

one request with 'specialPathParamOne' should go to the new endpoint and another one with 'specialPathParamTwo' should go to the old one.

Trying to find a way to implement it in VCL somehow...

Any tips and tricks here? Thanks a lot!

Answer 1

Actually, I received an answer on Fastly support forum: https://support.fastly.com/hc/en-us/community/posts/360045757132-Route-n-of-traffic-based-on-a-path-param

Writing my solution here:

I just need to calculate the percentage of '${specialPathParam}', this '${specialPathParam}' can be anything... So I have to randomize the requests around my '${specialPathParams}' which actually looks like randombool with seeded param:

Another function, randombool_seeded(), takes an additional seed argument. Results for a given seed will always be the same. https://docs.fastly.com/vcl/randomness/

So looks like I need something like:

if (randombool_seeded(X, 100, std.atoi('${specialPathParam}')) ) {
set req.backend = F_origin_0; } else { set req.backend = F_origin_1; }

and no need for headers.

So X percent of traffic will go to the backend 1 and requests with the same '${specialPathParam}' value would go to the same backend.