setting bereq.http headers in vcl_fetch doesn't work?

I'm trying to set some headers on the backend request, and it's not working.

https://developer.fastly.com/reference/vcl/variables/miscellaneous/bereq-http/

says "bereq.http.

STRING, can be read, set and unset.

but when I try to set a bereq,http header in vcl_fetch, it doesn't seem to do anything. I have a fiddle set up at https://fiddle.fastlydemo.net/fiddle/1d8cc830 which sets req.http.x-req-header in vcl_recv, and bereq.http.x-bereq-header in vcl_fetch. But you can see that the bereq.http.x-bereq-header never seems to get set. What's up?

Dara Roberts

August 27, 2020 18:29

Hi JD!

Great to hear from you again! Let me check this out for you.

I'll be back shortly.

Cheers,

Dara

September 01, 2020 19:09

Setting a bereq-header in fetch wouldn't change the header because the backend has already been called by the time fetch is run.

I used the fiddle to appended and set the bereq-header in miss and pass and both of those worked.

I do see in the documentation you linked that it doesn't clarify that it wont throw an error but that unset is what works in fetch and set would have no effect. I will get that clarified!

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