Set Host header for graphite-proxied requests to graphite host, not incoming host header

[GuillaumeConnan]

Due to an unresolved issue in the net/http/httputil package, Metrictrank can't reach a Graphite-Web fallback hosted behind an AWS application load balancer configured to route requests based on their host header.

The request's Host attribute, sent by Metrictank and read by the application load balancer, should match the request's URL.Host attribute to be correctly routed.

Currently, the Host attribute is set to the original request's host (the request made to Metrictank, which need to be proxified to Graphite).

This workaround replace the request's bad Host attribute with the expected value stored in URL.Host attribute.

[Dieterbe]

Currently, the Host attribute is set to the original request's host

the request's host? as in the hostname of the client? or did you mean the Hostname header set in the original request?

[GuillaumeConnan]

the Hostname header set in the original request

Given a client calling Metrictank's render API (on http://metrictank.internal/render for example).
The host header of this initial request is set to "metrictank.internal", everything is going as expected so far :-)

Then, if the request needs to be proxified by Metrictank to the Graphite fallback (on http://graphite-web.internal/render), the host header of the proxified request sent by Metrictank to Graphite is left untouched to "metrictank.internal" (the host header from the original request) when it should be set to "graphite-web.internal" to be correctly routed.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[Dieterbe]

LGTM. @shanson7 do you envision this may cause any breakage for you?

Note that we can't guarantee that all metrictank deployments will be okay with this change, so i have to asses the risk of this change for various deployments.

[shanson7]

I don't see this breaking our deploy