How to change base url used in responses from FHIR service when behind an Application Gateway

Danny Jones 5

We have a FHIR server running in an Azure Health Data Services workspace. The FHIR server is not accessible directly, all requests are routed through a public endpoint at an Application Gateway. This means the url of the FHIR server is not exposed or usable externally. When we make requests to the FHIR server via the application gateway, the responses contain hateoas links to things like the next page of search results, but those links are using the internal url and therefore do not work. Is it possible to configure the FHIR server or the Application Gateway so that those urls use the correct external base url?

MuthuKumaranMurugaachari-MSFT 22,151 Reputation points

2023-09-18T20:31:19.9+00:00

Danny Jones Sorry for the delay in response. These need to be configured in the application gateway. Have you already checked out Preserve the original HTTP host name between a reverse proxy and its back-end web application guidance? this is applicable to scenarios like HATEOAS.

If you are still looking for assistance, let us know.
Danny Jones 5 Reputation points

2023-09-18T21:39:42.7966667+00:00

Thanks for the response. We've tried various options in the backend settings for "Host name - Override with new host name". If we select No then every request returns 502 Bad Gateway.

If we select Yes and choose a specific Host Name other than the host name of the backend FHIR service i.e. xxx.fhir.azurehealthcareapis.com we get 502 Bad Gateway

If we select Yes and set the Host Name to the host name of the backend FHIR service then we get a correct response, but all the links in the response are internal links.

Have you ever used Application Gateway in front of an Azure Data Services FHIR service and been able to change the hostname to the external url? If so, what configuration specifically did you use to get this to work?
MuthuKumaranMurugaachari-MSFT 22,151 Reputation points

2023-09-19T14:49:34.7433333+00:00

Danny Jones Thanks for sharing the additional info. I see you have posted the same question in https://github.com/microsoft/fhir-server/issues/3526. I am reaching out to our product team regarding the same and we will keep you posted in Base url used in responses from FHIR service use internal urls when behind an Application Gateway thread.