Webservice does not work after being packaged into a Docker image - ruby

Question

I write a simple webservice in ruby with sinatra. If I run ruby app.rb it runs on localhost:4567. I write a Dockerfile to make an image and expose port 4567.
However, when I run the docker image the webservice runs but if I try to connect (with curl and browser) to port 4567, it says Connection reset by peer.
Anyone has any suggestion? Because I do not know what to check in this case. I have tried some vague things but still..
The webservice runs normally outside docker.
EDIT 1:
I have pushed the image to eivor/ruby. If you run it and go to browser to check it would say connection reset. Yes I tried docker run -p 4567:4567 eivor/ruby as said before posting the question.
EDIT 2: Here is the app.rb
require 'sinatra'
require 'referal' # this is the gem that calculate reward points to users
require 'json'
require 'byebug'
get '/' do
'hello, world!'
end
# inside docker image, even get / returns connection reset by peer
# not to mention post data to it
post '/' do
data = JSON.parse(request.body.read)
input = []
data.each do | key, value |
input << value
end
invs, users = input.reduce([[],[]]) do | results, instruction |
results = classify(instruction, results[0], results[1])
results
end
res = export(users)
# byebug
puts res
end
post '/text' do
#data = request.body.readlines
#byebug
#processed = #data.map{ |s| process(s) }
#invs, #users = #processed.reduce([[],[]]) do | results, instruction |
results = classify(instruction, results[0], results[1])
results
end
#jsn = export(#users)
puts #jsn
end
Here is the Dockerfile, i build a lightweight ruby from alpine
FROM alpine:3.5
ENV BUILD_PACKAGES bash curl-dev ruby-dev build-base git libstdc++ tzdata ca-certificates
ENV RUBY_PACKAGES ruby>2.3 ruby-irb ruby-rake ruby-io-console ruby-bigdecimal ruby-json
RUN apk update && apk upgrade
RUN apk add $BUILD_PACKAGES && apk add $RUBY_PACKAGES
RUN apk add ruby-bundler>1.17
RUN echo 'gem: --no-document' > /etc/gemrc && rm -rf /var/cach/apk/*
RUN gem install bundler
RUN mkdir /usr/app
WORKDIR /usr/app
RUN git init
COPY . /usr/app
RUN bundle install
RUN bundle exec rake install
EXPOSE 4567
CMD ["ruby", "./app.rb"]
If I run outside docker with command ruby app.rb or bundle exec rerun app.rb it works normally. But using docker image, it does not. I run the command:
docker run -p 4567:4567 eivor/ruby
The server runs,
[2019-03-14 16:59:59] INFO WEBrick 1.3.1
[2019-03-14 16:59:59] INFO ruby 2.3.8 (2018-10-18) [x86_64-linux-musl]
== Sinatra (v2.0.5) has taken the stage on 4567 for development with backup from WEBrick
[2019-03-14 16:59:59] INFO WEBrick::HTTPServer#start: pid=1 port=4567
but when I try to access with browser or curl, it says connection reset by peer. If I try to post with curl, the data is actually sent but it does not respond, it hangs up on me instead.
curl -v localhost:4567 --data-binary #test/input
* Rebuilt URL to: localhost:4567/
* Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to localhost (127.0.0.1) port 4567 (#0)
> POST / HTTP/1.1
> Host: localhost:4567
> User-Agent: curl/7.58.0
> Accept: */*
> Content-Length: 369
> Content-Type: application/x-www-form-urlencoded
>
* upload completely sent off: 369 out of 369 bytes
* Recv failure: Connection reset by peer
* stopped the pause stream!
* Closing connection 0
curl: (56) Recv failure: Connection reset by peer

Answer 1

This issue is happening because Sinatra by default (development environment) listen on 127.0.0.1 which not works in case of external connection to container
:bind - server hostname or IP address
String specifying the hostname or IP address of the interface to listen on when the :run setting is enabled. The default value in the development environment is 'localhost' which means the server is only available from the local machine. In other environments the default is '0.0.0.0', which causes the server to listen on all available interfaces.
So if you will continue on running in development mode, you need to change it to 0.0.0.0, for example:
docker run -p 4567:4567 --name stack eivor/ruby bash -c 'ruby ./app.rb -o 0.0.0.0'
Which can be used in Dockerfile as:
CMD ["ruby", "./app.rb", "-o", "0.0.0.0"]
Or you can use the following within your script:
set :bind, '0.0.0.0'
Then from outside the container you can get the result:
curl -v localhost:4567
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 4567 (#0)
> GET / HTTP/1.1
> Host: localhost:4567
> User-Agent: curl/7.64.0
> Accept: */*
>
< HTTP/1.1 200 OK
< Content-Type: text/html;charset=utf-8
< Content-Length: 13
< X-Xss-Protection: 1; mode=block
< X-Content-Type-Options: nosniff
< X-Frame-Options: SAMEORIGIN
< Server: WEBrick/1.3.1 (Ruby/2.3.8/2018-10-18)
< Date: Thu, 14 Mar 2019 17:17:20 GMT
< Connection: Keep-Alive
<
* Connection #0 to host localhost left intact
hello, world!
For more configuration check the following: CONFIGURING SETTINGS

Answer 2

Have a look at this article: https://docs.docker.com/config/containers/container-networking/
In few words - try to publish your exposed ports via -p argument.
For example:
$ docker run -it -p 4567 my-local-image

Answer 3

From the documentation:
Flag value Description
-p 8080:80 Map TCP port 80 in the container to port 8080 on the Docker host.
You need to map the TCP port 4567 in the container to a port on the Docker host. For example, to map it to port 8080:
$ docker run -it -p 8080:4567 image-goes-here