X-Forwarded-Host - support for including

Summary

Add support for X-Forwarded-Host header

Context

In some circumstances it is useful for upstream services to know the original host. For example imagine an api that returns the following json:

{
  "type": "articles",
  "id": "1",
  "attributes": {
    "title": "Rails is Omakase"
  },
  "relationships": {
    "author": {
      "links": {
        "self": "http://example.com/articles/1/relationships/author",
        "related": "http://example.com/articles/1/author"
      },
      "data": { "type": "people", "id": "9" }
    }
  },
  "links": {
    "self": "http://example.com/articles/1"
  }
}

Without access to a X-Forwarded-Host header the application would need to store the value http://example.com. This leads to extra unnecessary configuration

Further reading and context:

• X-Forwarded-Host on Mozilla developer network

Possible Implementation

Looking at the documenation it seems like we could add a new kind host to the existing Forwarded Header.

Adding the Forwarded header

Key	Default Value	Description
by	{kind: requestRandom}	The labeler to use with the router’s server address
for	{kind: requestRandom}	The labeler to use with the upstream client’s address
host	{kind: requestRandom}	The labeler to use with the host header, either host or connectionRandom

Additionaly a new labeler kind host could be added to write the host unobfuscated.

[ewilde]

I’ve also observed that if the X-Forwarded-Host is already set, linkerd forwards it on. Which in my particular case solves my scenario. I have kong api gateway infront of linkerd and have used the request transformer to add the X-Forwarded-Host header

[conanconstantine]

hey guys, do you know how to change the links in the payload (JSON API) based on the X-Forwarded-Host?