503 returned for requests to exact paths matched with "begins_with" about orm HOT 3 OPEN

Workaround

Use regex replace to set the request path without turning it into an empty string:

    actions:
      req_path:
        - replace:
            from_regex: /mypath/?(.*)
            to_regsub: /\1

from orm.

Available workaround

Below does not work in this case as the problem is that the path rewrite leaves an empty string. See below comment for a working req_path action.

Use a separate exact match to handle the problematic case explicitly:

from orm.

The root cause for the behaviour in this specific case is a rule on the form:

  - description: A VCL_Error generating rule
    domains:
      - example.com
    matches:
      all:
        - paths:
            begins_with:
              - "/path"
    actions:
      backend:
        origin: https://some.domain.example.com
      req_path:
        - prefix:
            remove: '/path'

A request to https://example.com/path makes the variable path in Varnish to "" and later there will be a set req.url = variable.get("path"); which is not allowed because it triggers

--  VCL_Error      Setting req.url to empty string

So to fix this there needs to be some check for the empty string in the path variable. Something like

if (variable.get("path") != "") {
  set req.url = variable.get("path");
} else {
  set req.url = "/";
}

from orm.