Docker - Failed to connect to localhost port 4000: Connection refused

Question

Hi I'm very new to Docker, I'm trying to get familiar with Docker by following the tutorial on official site. Now I get stuck at part 2 of the tutorial (where you can check up the link here => https://docs.docker.com/get-started/part2/#run-the-app)

I have sample application code, Dockerfile, and requirements.txt exactly same as the offical tutorial

$ ls
app.py  Dockerfile  requriements.txt

My Dockerfile looks like this

FROM python:2.7-slim
WORKDIR /app
ADD . /app
RUN pip install -r requriements.txt
EXPOSE 80
ENV NAME World
CMD ["python", "app.py"]

All 3 files have file content/code exactly same as the tutorial also. I was able to build image registry with this command

$ docker build -t friendlyhello .

Everything looks great. Now I had sample project image registry.

$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED
friendlyhello       latest              82b8a0b52e91        39 minutes ago
python              2.7-slim            1c7128a655f6        5 days ago
hello-world         latest              48b5124b2768        4 months ago

I then ran the app according to the official tutorial with this command

$ docker run -d -p 4000:80 friendlyhello
c1893f7eea9f1b708f639653b8eba20733d8a45d3812b442bc295b43c6c7dd5c

Edit: This is my container after ran above command

$ docker ps -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS
c1893f7eea9f        friendlyhello       "python app.py"     15 minutes ago      Up 16 minutes

And the official tutorial guides readers to have a look at http://localhost:4000 as they have already mapped machine port 4000 to container port 80

Unfortunately, I couldn't get any response from that URL.

$ curl http://localhost:4000
curl: (7) Failed to connect to localhost port 4000: Connection refused

I'm totally newbie and I have no idea what to do....How can I get it to work ? Thanks in advance for any response.

Edit: I did as @johnharris85 suggested. Below is the output

$ curl http://$(echo docker-machine ip default):4000
curl: (6) Couldn't resolve host 'docker-machine'
curl: (6) Couldn't resolve host 'ip'
curl: (6) Couldn't resolve host 'default'

It seems like it doesn't work either.

Edit: @johnharris85 corrected his suggestion and @user8023051 clarify how this command come from and what is going on under the hood. It is working now :) Thanks

$ curl http://$(docker-machine ip default):4000
<h3>Hello World!</h3><b>Hostname:</b> c1893f7eea9f<br/><b>Visits:</b> <i>cannot connect to Redis, counter disabled</i>

Answer 1

I'm not very familiar with docker, but it sounds like your setup is such that your docker instance is running in a virtual machine, and you're trying to access an application bound to localhost (the vm) from your Windows machine. The reason you would get a refusal here from curl is because nothing is actually listening on port 4000 on the host (Windows).

Try to find the IP that your docker instance is using by:

$ docker-machine ip default

Now that you know the IP address, try curl again. You can even have it evaluated within the command like so:

$ curl http://$(docker-machine ip default):4000

Answer 2

if you are running your docker on Mac and trying to connect to your dependancies (postgres etc) using localhost, replace localhost with docker.for.mac.localhost