Preserve host through reverse proxy

[jezen]

There are cases when it is desirable to preserve the Host header when implementing a reverse proxy.

Here's how this looks with other popular reverse proxies.

# nginx
proxy_set_header Host $http_host;

# Apache2
ProxyPreserveHost On

In the general case [IIUC], it is desirable to strip the Host header, as keter does. But I think this should be configurable, so I would propose an extension to ReverseProxyConfig such that in keter.yml, you could tell keter not to strip that header by writing something like this:

  - type: reverse-proxy
    reversed-host: localhost
    reversed-port: 3000
    reversed-ssl: false
    reversing-host: sub.domain.com
    preserve-host: true
    ssl:
      key: /etc/letsencrypt/live/domain.com/privkey.pem
      certificate: /etc/letsencrypt/live/domain.com/fullchain.pem

[jappeace]

you could do this by adding a config field there:

keter/src/Keter/Rewrite.hs

Line 171 in 58e898f

<$> o .: "reversed-host"

and then just pass it to the filter header function (instead of always false whatever the config setting is).
by default (or omission) it needs to be set to false.

[jezen]

Yeah, that's pretty much exactly how I'd approach this, and I intend to work on this myself. Just documenting here for the sake of posterity 🙂