How to configure nginx.ingress.kubernetes.io/rewrite-target and spec.rules.http.paths.path to satisfy the following URI patterns

The nginx.ingress.kubernetes.io/rewrite-target annotation is used to indicate the target URI where the traffic must be redirected. As per how I understand your question, you only want to match the URI patterns that you specified without redirecting the traffic. In order to achieve this, you can set the nginx.ingress.kubernetes.io/use-regex annotation to true, thus enabling regular expressions in the spec.rules.http.paths.path field.

Let's now take a look at the regex that you will need to match your URI patterns.First of all, the regex engine used by ingress-nginx doesn't support backreferences, therefore a regex like this one will not work. This is not a problem as you can match the /aa-bb/aa part without forcing the two aas to be equal since you will —presumably— still have to check the correctness of the URI later on in your service (e.g /us/en-us may be accepted whereas /ab/cd-ab may not).

You can use this regex to match the specified URI patterns:

/[a-z]{2}/[a-z]{2}-[a-z]{2}/coolapp(/.*)?

If you want to only match URL slugs in the cc part of the pattern you specified, you can use this regex instead:

/[a-z]{2}/[a-z]{2}-[a-z]{2}/coolapp(/[a-z0-9]+([a-z0-9]+)*)?

Lastly, as the nginx.ingress.kubernetes.io/use-regex enforces case insensitive regex, using [A-Z] instead of [a-z] would lead to the same result.

Follows an ingress example definition using the use-regex annotation:

apiVersion: extensions/v1beta1kind: Ingressmetadata:  name: test-regex  annotations:    nginx.ingress.kubernetes.io/use-regex: "true"spec:  rules:  - host: test.com    http:      paths:      - path: /[a-z]{2}/[a-z]{2}-[a-z]{2}/coolapp(/.*)?        backend:          serviceName: test          servicePort: 80

You can find more information about Ingress Path Matching in the official user guide.

Came up with the following configuration - it is working for all of my test routes / requirements so far.

The regex is almost the same as the one posted by @Gilgames.

I based mine on the official docs rewrite example: https://kubernetes.github.io/ingress-nginx/examples/rewrite/#rewrite-target

Apart from that I took a quick course at https://www.regular-expressions.info/ 😁

apiVersion: extensions/v1beta1kind: Ingressmetadata:  name: test-ing  namespace: some-ns  annotations:    kubernetes.io/ingress.class: nginx    nginx.ingress.kubernetes.io/rewrite-target: /$1/$2-$3/$5    certmanager.k8s.io/cluster-issuer: letsencrypt-prod    nginx.ingress.kubernetes.io/affinity: "cookie"    nginx.ingress.kubernetes.io/session-cookie-name: "INGRESSCOOKIE"    nginx.ingress.kubernetes.io/session-cookie-path: /    nginx.ingress.kubernetes.io/from-to-www-redirect: "true"    nginx.ingress.kubernetes.io/configuration-snippet: |        if ($host = 'example.com')        {            rewrite ^ https://www.example.com$request_uri permanent;        }spec:  tls:  - hosts:    - www.example.com    - example.com    secretName: tls-secret-test  rules:  - host: www.example.com    http:      paths:      - path: /([a-z]{2})/([a-z]{2})-([a-z]{2})/coolapp(/|$)(.*)        backend:          serviceName: coolapp-svc          servicePort: 80  - host: example.com    http:      paths:      - path: /([a-z]{2})/([a-z]{2})-([a-z]{2})/coolapp(/|$)(.*)        backend:          serviceName: coolapp-svc          servicePort: 80