This container will run one or many webservers, each of them listening on a single port.
Ports are specified using the `WEB_PORTS` environment variable:
docker run -d -e WEB_PORTS=80 web # will create a container running one webserver listening on port 80
docker run -d -e WEB_PORTS="80 81" web # will create a container running two webservers, one listening on port 80 and a second one listening on port 81
This is an optional requirement which is usefull if you cannot (or don't want to) install pytest and its requirements on your computer. In this case, you can use the `nginx-proxy-tester` docker image to run the test suite from a Docker container.