Supports full regexes when using Kubernetes as a backend

[kedare]

Do you want to request a feature or report a bug?

Feature

What did you do?

When trying to setup a pseudo wildcard or a regex on a Kubernetes ingress, the Kubernetes validation on the "host" field reject anything complicated (That is supported by Traefik, like regexes)

Example of ingress controller

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: templates-ssr-ingress
  annotations:
    kubernetes.io/ingress.class: traefik
    traefik.backend.circuitbreaker.expression: "NetworkErrorRatio() > 0.5"
spec:
  rules:
  - host: "npreview-{subdomain:[a-z]+}.xxxx.com"
    http:
      paths:
      - backend:
          serviceName: templates-ssr-service
          servicePort: 5050

What did you expect to see?

The correct information passed to Traefik, and the frontend set correctly

What did you see instead?

When trying to use regexes

The Ingress "templates-ssr-ingress" is invalid: spec.rules[0].host: Invalid value: "npreview-{subdomain:[a-z]+}.xxxx.com": a DNS-1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*')

When trying to use pseudo-wildcards

The Ingress "templates-ssr-ingress" is invalid: spec.rules[0].host: Invalid value: "npreview-*.xxx.com": a wildcard DNS-1123 subdomain must start with '*.', followed by a valid DNS subdomain, which must consist of lower case alphanumeric characters, '-' or '.' and end with an alphanumeric character (e.g. '*.example.com', regex used for validation is '\*\.[a-z0-9]([-a-z0-9]*[a-z0-9])?(\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*')

Output of traefik version: (What version of Traefik are you using?)

v1.4.2 (as Kubernetes Ingress Controller)

What is your environment & configuration (arguments, toml, provider, platform, ...)?

Using Kubernetes as backend.
Traefik a Ingress Controller

If applicable, please paste the log output in debug mode (--debug switch)

No log to show as the config doesn't reach Traefik

[kedare]

Related to kubernetes/kubernetes#41881

[nmengin]

WDYT @containous/kubernetes ?

[timoreimann]

AFAIU, the upstream issue referenced in #2408 (comment) seems to block us from making the host field support arbitrary regular expressions. Only subdomains seem to be possible right now.

If the feature request is about full regex support (which is how I understand it, but correct me if I'm wrong @kedare), I see two options: drive a possible extension of the supported patterns upstream, or introduce a custom annotation that hosts whatever pattern we want to support. Personally I'm not too fond of the idea of coming up with yet another custom annotation -- the Ingress feature space is already fairly fractured.

We should also check how Nginx deals with the situation.

[dtomcej]

@kedare,

Unfortunately Kubernetes never moved forward with allowing regexes to be used in ingresses.

This forced many providers to move to CRDs to provide this functionality.

With the release of Traefik v2, the IngressRoute CRD supports full regex matching to provide this functionality.

For this reason, I will be closing this issue.