How to implement multiple domain routing based on a custom field in request header properly?

Hi, could someone please suggest the proper way to implement multiple domain routing based on a custom field in request header?

My use case is, I have a service located in 2 different regions,resulting in two separate AWS ELBs: KR ELB and SG ELB. When FE sends requests to the service, the request header includes a field named region, which we’ll use to determine which ELB the request should connect to. We have identified two ways to implement regional routing:

  1. Origin Rules
  2. CF workers

for #1, it appears to perfectly meet our requirements by allowing us to define a rule and override the domain. no code work, GUI configuration, no additional cost. it’s great. unfortunately, seems it doesn’t support a custom field in request header yet. we have to use a existing field instead of a custom field. (as a workaround, we can put the field in query string which is supported by Origin Rules, but it’s not ideal from a design perspective)

for #2, CF worker is highly flexible, we’ve used it to implement various functionalities like caching, redirecting, etc. it’s easy to implement a worker for routing requests based on a field in request header. but we do have some concerns. such as:

  • the new worker needs to match all traffic (with a route like route =*) which could potentially increase latency, cost, affected scope
  • we need to implement the code ourselves and carefully consider the proper way to chain multiple workers, as this process could lead to potential bugs

Could anyone kindly share any ideas about this? I would greatly appreciate it


Though not available in the dropdown menu of the Expression Builder, you can use the http.request.headers fields in the Expression Editor.

( eq "")
any(http.request.headers["some-header"][*] == "some-value")

Host override with Origin Rules requires Enterprise Plan level.

As for the Workers route, you should join Cloudflare developers Discord channel where you’ll more likely to get feedback on whatever code you’re trying.


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