Does Traefik Utilize the HTTPS_PROXY Environment Variable for Backend Communication?

Traefik Traefik v3 (latest)
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Hello,

I'm trying to understand how Traefik handles proxy settings for communicating with backend servers. After reviewing the source code, I noticed that Traefik implements two types of reverse proxies: one using github.com/valyala/fasthttp (referred to as fast), and another using net/http/httputil (referred to as httputil).

From what I can gather:

  • The fast reverse proxy utilizes http.ProxyFromEnvironment to determine the proxy settings.
  • The httputil reverse proxy does not seem to use http.ProxyFromEnvironment.

Additionally, I observed that the smart_build component chooses to build the fast proxy if the following condition evaluates to false:

targetURL.Scheme == "h2c" || (targetURL.Scheme == "https" && !serversTransport.DisableHTTP2)

Based on this, it appears that Traefik might use the forward proxy settings defined in the HTTP_PROXY and HTTPS_PROXY environment variables when the above condition evaluates to false. Is my understanding correct? Could someone please confirm or correct my interpretation?

Thank you!