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How To Rewrite URLs To Lowercase In Nginx Controller On Kubernetes

I have a requirement to rewrite all URLs to lowercase.

E.g. test.com/CHILD to test.com/child

Frontend application is developed on docker on azure kubernetes services. Ingress is controlled on nginx ingress controller.

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Answer

You can rewrite URLs using Lua as described in the Enforce Lower Case URLs (NGINX) article.

All we need to do is add the following configuration block to nginx:

location ~ [A-Z] {
    rewrite_by_lua_block {
        ngx.redirect(string.lower(ngx.var.uri), 301);
    }
}

I will show you how it works.


First, I created an Ingress resource with the previously mentioned configuration:

$ cat test-ingress.yaml
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: test-ingress
  annotations:
    kubernetes.io/ingress.class: nginx
    nginx.ingress.kubernetes.io/rewrite-target: /
    nginx.ingress.kubernetes.io/server-snippet: |
     location ~ [A-Z] {
        rewrite_by_lua_block {
            ngx.redirect(string.lower(ngx.var.uri), 301);
        }
      }
spec:
  rules:
  - http:
      paths:
      - path: /app-1
        pathType: Prefix
        backend:
          service:
            name: app-1
            port:
              number: 80
              
              
$ kubectl apply -f test-ingress.yaml
ingress.networking.k8s.io/test-ingress created

$ kubectl get ing
NAME           CLASS    HOSTS   ADDRESS          PORTS   AGE
test-ingress   <none>   *       <PUBLIC_IP>      80      58s

Then I created a sample app-1 Pod and exposed it on port 80:

$ kubectl run app-1 --image=nginx
pod/app-1 created

$ kubectl expose pod app-1 --port=80
service/app-1 exposed

Finally, we can test if rewrite works as expected:

$ curl -I <PUBLIC_IP>/APP-1
HTTP/1.1 301 Moved Permanently
Date: Wed, 06 Oct 2021 13:53:56 GMT
Content-Type: text/html
Content-Length: 162
Connection: keep-alive
Location: /app-1

$ curl -L <PUBLIC_IP>/APP-1
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
...

Additionally, in the ingress-nginx-controller logs, we can see the following log entries:

10.128.15.213 - - [06/Oct/2021:13:54:34 +0000] "GET /APP-1 HTTP/1.1" 301 162 "-" "curl/7.64.0" 83 0.000 [-] [] - - - - c4720e38c06137424f7b951e06c3762b
10.128.15.213 - - [06/Oct/2021:13:54:34 +0000] "GET /app-1 HTTP/1.1" 200 615 "-" "curl/7.64.0" 83 0.001 [default-app-1-80] [] 10.4.1.13:80 615 0.001 200 f96b5664765035de8832abebefcabccf
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source: stackoverflow.com
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