[nginx] Redirect with added trailing slash

[himikof]

Nginx by default automatically adds HTTP redirect /foo -> /foo/ when using prefix match with trailing slash location /foo/ which is redirected to a backend (documented in the last paragraph here). This behavior is useful when serving a web application at http://example.com/foo/ and a user accesses http://example.com/foo. Unfortunately, this behavior is broken when using ingress.kubernetes.io/rewrite-target annotation, which turns location match into a non-prefix regex one.
I would argue that the behavior of adding a trailing slash by HTTP redirect on the base path of an web application exposed through an non-root Ingress (with or without a rewrite target) is very useful and should either work by default, or be enabled via some separate annotation.
I was unable to find a workaround in the latest version of Nginx ingress controller. Using /foo ingress path does not work as it breaks relative links inside the web application.
Also, if #619 would be fixed by unconditionally enabling regular expressions, even the currently working cases (without rewrite) will break.

[rutsky]

Related: kubernetes-retired/contrib#1884

As a workaround ingress.kubernetes.io/configuration-snippet can be used (based on this comment by @hartmut-co-uk):

---
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: app
  annotations:
    ingress.kubernetes.io/rewrite-target: /
    # adds 301 redirect with trailing slash
    ingress.kubernetes.io/configuration-snippet: |
      rewrite ^(/app)$ $1/ permanent;
spec:
  rules:
  - host: example.com
    http:
      paths:
      - path: /app
        backend:
          serviceName: app
          servicePort: 80

This works with ingress.kubernetes.io/rewrite-target: / probably by accident, the configuration snippet is being added just before other rewrite rules:

# Parts of generated /etc/nginx/nginx.conf

        location ~* ^/app {
            set $proxy_upstream_name "default-routes-app-80";
            port_in_redirect off;

            # enforce ssl on server side
            if ($pass_access_scheme = http) {
                return 301 https://$host$request_uri;
            }

# ...

            rewrite ^(/app)$ $1/ permanent;
        rewrite /app/(.*) /$1 break;
        rewrite /app / break;
        proxy_pass http://default-routes-app-80;

        }

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[ProProgrammer]

Further to what @rutsky mentioned in his comment if you are using nginx ingress controller specifically and your annotations start with nginx as follows:

  name: ingress-tutorial
  annotations:
    kubernetes.io/ingress.class: "nginx"
    nginx.ingress.kubernetes.io/rewrite-target: "/"
    nginx.ingress.kubernetes.io/configuration-snippet: |
      rewrite ^(/app)$ $1/ permanent;

Your annotation should start with nginx. and hence should read as nginx.ingress.kubernetes.io/configuration-snippet as opposed to ingress.kubernetes.io/configuration-snippet

[Glathrop]

Please keep in mind that while @ProProgrammer 's solution works 301 redirects are PERMANENT.

The unintended byproducts of forcing a trailing slash via 301 can be enough to get you fired.

It's likely safer to start with a 302 temporal redirect if you're just futzing around trying to get something operational.

Per the NGINX docs you can use the redirect param instead of the permanent param to provide a 302 instead of a 301 redirect.

  name: ingress-tutorial
  annotations:
    kubernetes.io/ingress.class: "nginx"
    nginx.ingress.kubernetes.io/rewrite-target: "/"
    nginx.ingress.kubernetes.io/configuration-snippet: |
      rewrite ^(/app)$ $1/ redirect;

[nabeelio]

I can't quite get that rewrite rule/block to work. It redirects me to the (internal) load balancer IP.

Is there another config to explicitly set the host? nginx doesn't work if I specify the host (there's an internal load balancer), I think the DNS name is getting dropped from the public load balancer.

[ahmadalli]

for anyone who's checking this issue, the annotation is now changed to nginx.ingress.kubernetes.io/configuration-snippet

[Vyom-Yadav]

If you are wondering how rewrite ^(/app)$ $1/ permanent; works, give https://www.nginx.com/blog/creating-nginx-rewrite-rules/ a read.