# Traefik routed requests to second container are rejected

**URL:** <https://community.traefik.io/t/traefik-routed-requests-to-second-container-are-rejected/16071>\
**Category:** Traefik v2\
**Tags:** docker\
**Created:** [October 9, 2022, 2:04pm UTC](https://community.traefik.io/t/traefik-routed-requests-to-second-container-are-rejected/16071 "2022-10-09T14:04:40Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Fred](https://avatars.discourse-cdn.com/v4/letter/f/db5fbb/32.png) [@Fred](https://community.traefik.io/u/Fred)\
**Post date:** [October 9, 2022, 2:04pm UTC](https://community.traefik.io/t/traefik-routed-requests-to-second-container-are-rejected/16071/1 "2022-10-09T14:04:40Z")

</div>

A flask app consists of two docker containers, app-frontend & app-backend (these are the actual container names), behind a traefik v2 rev proxy. URL [https://app.com](https://app.com) is routed to app-frontend, and [https://app.com/api](https://app.com/api) is routed to app-backend. app-frontend makes requests to app-backend via [https://app.com/api](https://app.com/api). The rev-proxy & both app containers are all within the same docker network.

Replacing the rev proxy with apache, the following vhosts config works as expected:

```auto
ProxyPass "/api" "http://app-backend:5000/"
ProxyPassReverse "/api" "http://app-backend:5000/"
ProxyPass "/" "http://app-frontend:80/"
ProxyPassReverse "/" "http://app-frontend:80/"

```

Running with this traefik config in docker-compose.yml labels:

```auto
    # app-backend labels:
    labels:
      - "traefik.enable=true"
      - "traefik.http.routers.app-backend-https.rule=Host(`app.com`) && PathPrefix(`/api`)"
      - "traefik.http.routers.app-backend-https.entryPoints=web-secure"
      - "traefik.http.routers.app-backend-https.tls=true"
      - "traefik.http.routers.app-backend-https.service=app-backend"
      - "traefik.http.services.app-backend.loadbalancer.server.scheme=http"
      - "traefik.http.services.app-backend.loadbalancer.server.port=5000"

```

```auto
    # app-frontend labels:
    labels:
      - "traefik.enable=true"
      - "traefik.http.routers.app-frontend-https.rule=Host(`app.com`) && !PathPrefix(`/api`)"
      - "traefik.http.routers.app-frontend-https.entryPoints=web-secure"
      - "traefik.http.routers.app-frontend-https.tls=true"
      - "traefik.http.routers.app-frontend-https.service=app-frontend"
      - "traefik.http.services.app-frontend.loadbalancer.server.port=80"

```

With this configuration, requests to app-frontend work as expected.  
Requests to app-backend appear to be routed to the correct container:

`app-backend | 172.18.0.2 - - [09/Oct/2022 13:01:18] "GET /api/config HTTP/1.1" 404 -`

but it always respands with status 404 and the message:

`The requested URL was not found on the server. If you entered the URL manually please check your spelling and try again.`

I've not been able to intercept the processing in the backend as this seems to be handled by flask, the destination function is never reached.

I have a suspition that apache may be passing the host as name `app-backend:5000` in the request while traefik's docker provider is passing it using the equivlent IP, and that flask is rejecting requests with the IP - but this is a stab in the dark. I'm not aware of any way of overriding the docker IP with the container name in traefik - but as already mentioned - this may not be the issue....

Does anyone have suggestions / ideas why the traefik config would fail when the apache proxy config succeeds?

---

<div class="post-metadata">

**Author:** ![kevinpollet](https://sea2.discourse-cdn.com/flex020/user_avatar/community.traefik.io/kevinpollet/32/1755_2.png) [@kevinpollet](https://community.traefik.io/u/kevinpollet)\
**Post date:** [October 10, 2022, 3:24pm UTC](https://community.traefik.io/t/traefik-routed-requests-to-second-container-are-rejected/16071/2 "2022-10-10T15:24:11Z")

</div>

Hello @Fred and thanks for your interest in Traefik,

> I have a suspition that apache may be passing the host as name app-backend:5000 in the request while traefik's docker provider is passing it using the equivlent IP, and that flask is rejecting requests with the IP - but this is a stab in the dark. I'm not aware of any way of overriding the docker IP with the container name in traefik - but as already mentioned - this may not be the issue....

By default, Traefik is forwarding the request Hosts (in your case `app.com`) to the backend. In case one wants to change that behavior the `passHostHeader` option can be disabled as explained in the following documentation: [Traefik Services Documentation - Traefik](https://doc.traefik.io/traefik/routing/services/#pass-host-header). Therefore, the forwarded Host will be `app-backend:5000`.

Hope this helps!

---

<div class="post-metadata">

**Author:** ![Fred](https://avatars.discourse-cdn.com/v4/letter/f/db5fbb/32.png) [@Fred](https://community.traefik.io/u/Fred)\
**Post date:** [October 11, 2022, 8:53am UTC](https://community.traefik.io/t/traefik-routed-requests-to-second-container-are-rejected/16071/3 "2022-10-11T08:53:20Z")

</div>

Problem solved: What I had missed was that the apache line:

```
`ProxyPass "/api" "http://app-backend:5000/"`

```

actually **removes** the `/api` prefix, whereas traefik was correctly matching it but forwarding the request with the prefix still present. So, added the following lines to strip the prefix, and everything started working:

```auto
   - "traefik.http.middlewares.test-stripprefix.stripprefix.prefixes=/api"
   - "traefik.http.routers.app-backend-https.middlewares=test-stripprefix"

```