Add support to remove path prefix when proxying to backend

[zdila]

I would like http://example.com/foo/bar to be proxied as http://127.0.0.1:8080/bar - ie. I wan to strip /foo from the path going to the backend. Is it possible?

Without stripping:

[[clusters.sig.frontends]]
address = "0.0.0.0:80"
hostname = "example.com"
path = "/foo"

[[clusters.sig.backends]]
address = "127.0.0.1:8080"

[Wonshtrum]

Unfortunately this is not currently possible, but very soon it will be!
We are introducing authentication, redirection, and rewriting in the next release.
You can check issue #1161 on that subject and corresponding PR #1162.
If you want you can use the branch of this PR, it should be fully working, we are doing last performance and compatibility checks before merging it. Note that the authentication part may change, but the rewrite part is complete as far as we know.

For your specific use case, on this branch you can configure your cluster with the following frontend:

[[clusters.sig.frontends]]
address = "0.0.0.0:80"
hostname = "example.com"
path = "/foo"
rewrite_path = "$PATH[1]"

Beware with this example, the default PREFIX path rule matches any path that start with this pattern, so /foo and /foobar will match and redirect to 127.0.0.1:8080 and 127.0.0.1:8080bar respectively.
You may want to use the /foo/ prefix (but it doesn't match /foo), or to use 2 frontends, or a more complex REGEX path rule:

[[clusters.sig.frontends]]
address = "0.0.0.0:80"
hostname = "example.com"
path_type = "REGEX"
path = "/foo(/.*)?"
rewrite_path = "$PATH[1]"