Traefik

Basics

backend (URL to origin) is uncontrollable
doesn't care about the verb
doesn't support TRACE
doesn't support Max-Forwards
doesn't support HTTP/0.9
set HTTP/1.1 for the backend by default
doesn't allow >1 Host header (400 Bad Request: too many Host headers)
doesn't allow 0x0d in header value
adds headers to the request to origin: X-Forwarded-For, X-Forwarded-Host, X-Forwarded-Port, X-Forwarded-Proto, X-Forwarded-Server, X-Real-Ip
- if we send our headers with the same names (X-Forwarded-Host, X-Forwarded-Port, X-Forwarded-Proto, X-Real-Ip), we overrides values of proxy's request
- in case of X-Forwarded-For, it will be added to proxy's request (examplezzz.com, example2.com)
- in case of X-Replaced-Path (see below), there will be two header with X-Replaced-Path name
forwards headers with underscore _ in name
forwards headers with trailing space, but deletes the space (AnyHeader :->AnyHeader:)
support line folding for headers ( Header:zzz-> it is concatenated with the previous header)
doesn't allow %2f as the first slash. It must be / or * only
doesn't allow space ( ) in the path
doesn't normalize the path
url decodes before applying matchers, forwards url encoded version to backend
/!"$&'()*+,-./:;<=>@[\]^_`{|}~#? -> $&+,s-./:;=@_~?, %21%22%27%28%29%2A%3C%3E%5B%5C%5D%5E%60%7B%7C%7D%23
0x00-0x19 -> %00-%19, >0x80 -> >%80
%00-%FF -> %00-%FF

400 Bad Request

Host: / -> 400 Bad Request: malformed Host header

Use Path if your backend listens on the exact path only (allows query string)
Use a *Prefix* (PathPrefix) matcher if your backend listens on a particular base path but also serves requests on sub-paths
Use a *Strip (PathPrefixStrip) matcher if your backend listens on the root path (/) but should be routeable on a specific prefix
AddPrefix: /products: Add path prefix to the existing request path prior to forwarding the request to the backend.
ReplacePath: /serverless-path: Replaces the path and adds the old path to the X-Replaced-Path header. Useful for mapping to AWS Lambda or Google Cloud Functions.
ReplacePathRegex: ^/api/v2/(.*) /api/$1: Replaces the path with a regular expression and adds the old path to the X-Replaced-Path header. Separate the regular expression and the replacement by a space.