Connection refused on docker container

Question

I'm new to Docker and trying to make a demo Rails app. I made a dockerfile that looks like this:

FROM ruby:2.2
MAINTAINER [email protected]

# Install apt based dependencies required to run Rails as 
# well as RubyGems. As the Ruby image itself is based on a 
# Debian image, we use apt-get to install those.
RUN apt-get update && apt-get install -y \
build-essential \
nodejs

    # Configure the main working directory. This is the base 
    # directory used in any further RUN, COPY, and ENTRYPOINT 
    # commands.
RUN mkdir -p /app
WORKDIR /app

    # Copy the Gemfile as well as the Gemfile.lock and install 
    # the RubyGems. This is a separate step so the dependencies 
    # will be cached unless changes to one of those two files 
    # are made.
COPY Gemfile Gemfile.lock ./
RUN gem install bundler && bundle install --jobs 20 --retry 5

# Copy the main application.
COPY . ./

# Expose port 8080 to the Docker host, so we can access it 
# from the outside.
EXPOSE 8080

# The main command to run when the container starts. Also 
# tell the Rails dev server to bind to all interfaces by 
# default.
CMD ["bundle", "exec", "rails", "server", "-b", "0.0.0.0", "-p", "8080"]

I then built it like so:

docker build -t demo . 

And call a command to start the server which does start the server on port 8080:

Johns-MacBook-Pro:demo johnkealy$ docker run -it demo
=> Booting WEBrick
=> Rails 4.2.5 application starting in development on http://0.0.0.0:8080
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
[2016-04-23 16:50:34] INFO  WEBrick 1.3.1
[2016-04-23 16:50:34] INFO  ruby 2.2.4 (2015-12-16) [x86_64-linux]
[2016-04-23 16:50:34] INFO  WEBrick::HTTPServer#start: pid=1 port=8080

I then try to find the correct IP to navigate to:

Johns-MacBook-Pro:demo johnkealy$ docker-machine ip default
192.168.99.100

I navigate to http://192.168.99.100:8080 and get the error This site can’t be reached 192.168.99.100 refused to connect.

What could I be doing wrong ?

Answer 1

You need to publish the exposed ports by using the following options:

-P (upper case) or --publish-all that will tell Docker to use random ports from your host and map them to the exposed container's ports.

-p (lower case) or --publish=[] that will tell Docker to use ports you manually set and map them to the exposed container's ports.

The second option is preferred because you already know which ports are mapped. If you use the first option then you will need to call docker inspect demo and check which random ports are being used from your host at the Ports section.

Just run the following command:

docker run -it -p 8080:8080 demo

After that your url will work.

Answer 2

If you are using Docker toolkit on window 10 home you will need to access the webpage through docker-machine ip command. It is generally 192.168.99.100:

It is assumed that you are running with publish command like below.

docker run -it -p 8080:8080 demo

With Window 10 pro version you can access with localhost or corresponding loopback 127.0.0.1:8080 etc (Tomcat or whatever you wish). This is because you don't have a virtual box there and docker is running directly on Window Hyper V and loopback is directly accessible.

Verify the hosts file in window for any digression. It should have 127.0.0.1 mapped to localhost

Answer 3

I had the same problem. I was using Docker Toolbox on Windows Home. Instead of localhost I had to use http://192.168.99.100:8080/.

You can get the correct IP address using the command:

docker-machine ip

The above command returned 192.168.99.100 for me.

Answer 4

In Docker Quickstart Terminal run following command:

$ docker-machine ip 192.168.99.100 

Answer 5

Command EXPOSE in your Dockerfile lets you bind container's port to some port on the host machine but it doesn't do anything else. When running container, to bind ports specify -p option.

So let's say you expose port 5000. After building the image when you run the container, run docker run -p 5000:5000 name. This binds container's port 5000 to your laptop/computers port 5000 and that portforwarding lets container to receive outside requests.

This should do it.