RedirectRegex returning gibberish in AWS ECS(Fargate)

[BogdanNic]

Welcome!

• Yes, I've searched similar issues on GitHub and didn't find any.
• Yes, I've searched similar issues on the Traefik community forum and didn't find any.

What did you do?

I created and deployed a traefik service into AWS ECS(Fargate) to help me with some regex redirects based on the path. The basic idea I sent it a url and traefik should parse the url get the regex group and then redirect to a new path based on a specific regex group.

What did you see instead?

Instead of the showing the regex groups and replacing them it shows the first group as $%7B1%7D

What version of Traefik are you using?

2.8.8 but also 2.9

What is your environment & configuration?

version: '3'

services:
  traefik:
    image: traefik:v2.9
    command:
      - "--providers.docker"
      - "--entrypoints.web.address=:80"
    environment:
      - TRAEFIK_PING=true
      - TRAEFIK_PING_ENTRYPOINT=web
      - TRAEFIK_ENTRYPOINTS_WEB=true
      - TRAEFIK_ENTRYPOINTS_WEB_ADDRESS=":80"
      - TRAEFIK_LOG_LEVEL=DEBUG
    ports:
      - "80:80"
      - "8080:8080"
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    labels:
      - "traefik.http.routers.redirect-router.entrypoints=web"
      - "traefik.http.routers.redirect-router.rule=Host(`myserver`)"
      - "traefik.http.routers.redirect-router.middlewares=redirect-regex"
      - "traefik.http.middlewares.redirect-regex.redirectregex.regex=^http://myserver/test-(.*)-mytest"
      - "traefik.http.middlewares.redirect-regex.redirectregex.replacement=http://myserver/test2-$${1}-mytest2"

Add more configuration information here.

If applicable, please paste the log output in DEBUG level

Not error showed.

[rtribotte]

Hello @BogdanNic,

Thanks for your interest in Traefik!

Usually, for labels, the dollar signs need to be doubled for escaping.
But, there are probably specificities with ECS Fargate that makes the escaping unnecessary.
$%7B1%7D is the encoded value of ${1}

Can you try not escaping the dollar sign in the replacement, as follows:
- "traefik.http.middlewares.redirect-regex.redirectregex.replacement=http://myserver/test2-${1}-mytest2"

[BogdanNic]

You are correct. It works with single dollar.