Docker - Bind for 0.0.0.0:4000 failed: port is already allocated

You need to make sure that the previous container you launched is killed, before launching a new one that uses the same port.

docker container ls
docker rm -f <container-name>

Paying tribute to IgorBeaz, you need to stop running the current container. For that you are going to know current CONTAINER ID:

$ docker container ls

You get something like:

CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS                  NAMES
12a32e8928ef        friendlyhello       "python app.py"     51 seconds ago      Up 50 seconds       0.0.0.0:4000->80/tcp   romantic_tesla   

Then you stop the container by:

$ docker stop 12a32e8928ef

Finally you try to do what you wanted to do, for example:

$ docker run -p 4000:80 friendlyhello

I solved it this way:

First, I stopped all running containers:

docker-compose down

Then I executed a lsof command to find the process using the port (for me it was port 9000)

sudo lsof -i -P -n | grep 9000

Finally, I "killed" the process (in my case, it was a VSCode extension):

kill -9 <process id>