Summary

The traefik docker container uses 100% CPU when it serves as its own backend, which is an automatically generated route resulting from the Docker integration in the default configuration.

Details

While attempting to set up Traefik to handle traffic for Docker containers, I observed in the webUI a rule with the following information:

Host(traefik-service) | webwebsecure | traefik-service@docker | traefik-service

I assumed that this is something internal; however, I wondered why it would have a host rule on the web entrypoint configured.

So I have send a request with that hostname with curl -v --resolve "traefik-service:80:xxx.xxx.xxx.xxx" http://traefik-service. That made my whole server unresponsive.

I assume the name comes from a docker container with that name, traefik itself:

localhost ~ # docker ps
CONTAINER ID   IMAGE                                                   COMMAND                  CREATED             STATUS         PORTS                                                                                                NAMES
d1414e74aec7   traefik:v2.10                                           "/entrypoint.sh trae…"   4 minutes ago       Up 4 minutes   0.0.0.0:80->80/tcp, :::80->80/tcp, 0.0.0.0:443->443/tcp, :::443->443/tcp, 127.0.0.1:8080->8080/tcp   traefik.service

PoC

1. Start traefik with docker run --rm -v /var/run/docker.sock:/var/run/docker.sock -p 80:80 --name foo -p 8080:8080 traefik:v2.10 --api.insecure=true --providers.docker

2. curl -v --resolve "foo:80:127.0.0.1" http://foo

looks like this creates an endless loop of request.

Knowing the name of the docker container seems to be enough to trigger this, if the docker backend is used.

Impact

Server is unreachable and uses 100% CPU