How can I write an NGINX Ingress rewrite rule with a literal question mark in Kubernetes?

When you need to include a literal question mark in a regular expression, you have to escape it with a backslash (i.e. ?). However, there are two important points to note:

1. YAML Escaping:
   Since your regex appears inside a YAML file, you often need an extra level of escaping. For a literal ? in YAML, you’ll likely need to write it as \? to ensure that the backslash is preserved.

2. Path vs. Query String:
   The NGINX Ingress Controller matches only the path portion of the request URL—not the query string. In your example, whether a client requests
   • example.com/ws?list=a,b,c
   or
   • example.com/ws/?list=a,b,c
   the matching part is just /ws or /ws/ (the part before the ?). This means that any regex pattern you write in the path that attempts to include the ? (or subsequent query details) isn’t going to match because the query string isn’t considered.

What to Do

• If your goal is to match both /ws and /ws/ regardless of the query string:
  You should use a pattern that allows an optional trailing slash. For example:

  YAMLCopied
  - path: ^/ws/?(.*)$
    pathType: ImplementationSpecific
    component: "{{ .Values.broadcaster.component }}"
    port: "{{ .Values.broadcaster.service.port }}"

  This regex matches both /ws and /ws/ and any additional path segments after the slash.
  (Make sure that your Ingress controller is configured to allow regex paths, usually with an appropriate annotation such as nginx.ingress.kubernetes.io/use-regex: "true".)

• If you absolutely need to have a literal question mark in your regex (for another use case):
  Escape it with a backslash. In YAML this likely means:

  YAMLCopied
  - path: /ws(\\?.*)
    pathType: ImplementationSpecific
    component: "{{ .Values.broadcaster.component }}"
    port: "{{ .Values.broadcaster.service.port }}"

  But remember, this rule won’t match URLs based on the query string because the Ingress matching only considers the path segment.

Conclusion

For your use case, it is best to match the path portion (e.g. /ws or /ws/) with an optional trailing slash. If you ever need a literal question mark in a regex, use \\? in your YAML file. Keep in mind that query parameters won’t be part of the matching process when using NGINX Ingress rules.