URL Variables as Docker Labels?

[polds]

Wondering if it's possible to do URL Variables as part of a Docker label like so:

docker run ... \
  --label traefik.frontend.rule=Host \
  --label traefik.frontend.value={subdomain:[a-z]+}.example.com \
  ...

[polds]

Looked into it a little more when trying to pass that as a Docker label the toml package throws the following error:

Error creating docker configuration Near line 8, key 'frontends': Near line 8: Table names cannot contain '[' or ']'.

Looks like because the entire frontend name is being used as per docker.tmpl it's attempting also inject the regex into the table name.

Please see the referenced commit for my fixes. If you think these are inline I can make a PR. I'm not exactly sure what to return with if the parsing failed. Right now it returns the original string (Don't like this)

[emilevauge]

Hi @polds, thank you for reporting. This is an issue. We have to find a smart way to do that. I'm not sure to understand what does:

"makeParsedUrl": func(s1 string) string {
            if u, err := url.Parse(s1); err == nil {
                return u.String()
            }
            return s1
        },

Could you explain a little bit ?

[polds]

@emilevauge it converts the string to their html entities counterparts. Going in the string is {subdomain: [a-z]+}.example.com and coming back it is converted to an ugly, but safe: %7Bsubdomain:%20%5Ba-z%5D+%7D.example.com but still parsed correctly by Traefik.

My biggest concern is if the url.Parse() fails I have it returning the same string which would inevitably cause issues if url.Parse() can't handle it. I'm wondering if just returning the string "error" would be better.

Edit: The TOML parser was only specifically complaining about the [ ] so perhaps instead of introducing a new template function we use the already available replace function and do something like so:

{{$frontend | replace "[" "" | replace "]" ""}}

[emilevauge]

@polds, OK I get it. I definitely prefer the second solution to reuse the replace template function. Would you make a PR on that point?

[emilevauge]

Or even better, should be added directly here: https://github.com/emilevauge/traefik/blob/master/provider/docker.go#L209