How to use stack image container?

Question

Stack can build a docker container to run your app on a server with the stack image container command (See references below).

How do I connect to the web server in the docker container created this way?

I've build a simple app to demonstrate the issue. See the complete code here: https://github.com/seanhess/haskell-docker-example

This app was built from stack new with minimal changes. Here's Main.hs

{-# LANGUAGE OverloadedStrings #-}
module Main where

import Network.Wai
import Network.HTTP.Types (status200)
import qualified Network.Wai.Handler.Warp as Warp

main :: IO ()
main = Warp.run 8010 app

app :: Application
app req respond = do
    (putStrLn $ "Request: " ++ (show req))
    (respond $ responseLBS status200 [] "Hello World")

And stack.yaml

resolver: nightly-2016-06-12

image:
  container:
    name: haskell-docker-example
    base: fpco/stack-run

This app responds with "Hello world" if you run it locally.

stack build
stack exec haskell-docker-example

But if you build the docker image and start it:

stack image container
docker run -it -p 8010:8010 haskell-docker-example

Requests reach the docker container, but we get an empty response error because there's nothing behind it.

$ curl -i http://localhost:8010
curl: (52) Empty reply from server

References:

• http://www.yesodweb.com/blog/2015/12/yesod-hosting-docker-kubernetes
• https://github.com/commercialhaskell/stack/issues/2337
• http://docs.haskellstack.org/en/stable/GUIDE/#docker

Update: I'm poking around more. When I attach to the running container, my app is definitely not running. If I attempt to execute it by hand I get the following error:

/usr/local/bin/haskell-docker-example-exe
bash: /usr/local/bin/haskell-docker-example-exe: cannot execute binary file: Exec format error

Some googling suggests this can come when trying to execute 64 bit code on a 32 bit system. Is that possible? If it matters I'm on mac osx.

Answer 1

The executable I was building locally (OSX) was not runnable on the docker container. The solution was to build with docker. I changed stack.yaml to the following:

# we have to switch to an LTS resolver, because the stack-build
# docker image doesn't support nightly. 
resolver: lts-6.6

docker:
  enable: true

image:
  container:
    name: haskell-docker-example
    base: fpco/stack-run

Then I rebuilt, now using the docker image

stack build
stack image container

And it runs great! Looks like you need to manually specify that you want to run the executable though:

docker run -it -p 8010:8010 haskell-docker-example /usr/local/bin/haskell-docker-example-exe

Alternatively, run stack with --docker, which will override the docker setting in stack.yml (also you don't need to run stack build separately):

stack --docker image container