Traefik redirect / (root) to sub path with Docker labels

traefik-redirect-path.md

Traefik: redirect base or root path to a subpath

This is tested with Traefik 1.7

This is how to redirect the root or base path to a sub path in Traefik using Docker labels:
Goals

• https://example.com -> https://example.com/abc/xyz/
• https://example.com/ -> https://example.com/abc/xyz/
• https://example.com/something -> no redirect

We will match <begin of line>https://<any chars but not slash AS group1><slash or nothing><end of line>
and replace it with https://<group1>/abc/xyz/.
In regex we have to escape a / character by \/. In docker-compose labels we need to escape again, so that it becomes \\\\/.
We also need to escape $ to $$ because of docker-compose.

labels:
  - "traefik.frontend.rule=Host:example.com"
  - "traefik.frontend.redirect.regex=^https:\\\\/\\\\/([^\\\\/]+)\\\\/?$$"
  - "traefik.frontend.redirect.replacement=https://$$1/abc/xyz/"
  - "traefik.port=80"
  - "traefik.enable=true"

I solved my problem. I used a Middleware k8s resource as follows:

apiVersion: traefik.containo.us/v1alpha1
kind: Middleware
metadata:
  name: replace-api-with-ngsi-ld
  namespace: default  
spec:
  replacePathRegex:
    regex: "^/api(.*)"
    replacement: "/ngsi-ld$1"

then I had to add in my Ingress the annotation: traefik.ingress.kubernetes.io/router.middlewares: default-replace-api-with-ngsi-ld@kubernetescrd and set:

- backend:
    service:
      name: scorpio
      port: 
        number: 9090
  path: /api
  pathType: Prefix

Thank you, I solved a root redirect for mailpit

http:
  middlewares:
    mailpit-mail-prefix:
      redirectRegex:
        regex: "^https://([^/]+)/?$"
        replacement: "https://${1}/mail/"