Running LFE in Docker

Update: This post has been updated to account for the recenrt changes in the newly published lfex/lfe Docker images. The examples given below in this post will no longer work as written … original post follows:

With the growing prominence of Docker in PaaS offerings, from Linode and OpenShift to Google and AWS, it is increasingly more crucial that open source projects support their users by offering images which make deploying their apps even easier. We've only just started doing this in the LFE community, but are already quite excited by the possibilities and the early successes we've seen.

We're currently working on an official LFE image for Docker, but in the mean time, we will demonstrate functionality with an image we've made available on the LFE Exchange in Docker Hub.

UPDATE: There is an updated blog post for the latest image. Please read that for the quickest possible use of the LFE YAWS Dockerized web app.

Background Info

For a wonderful intro to Docker, see last year's OpenShift blog post Day 21: Docker–The Missing Tutorial by Shekhar Gulati. Another fantastic resource is the Docker cheatsheet by Will Sargent of TypeSafe.

It goes without saying, but we want to say it anyway: all of the steps below are just as applicable for all languages running on the Erlang VM: LFE, Elixir, Joxa, Luerl, Erlog, Haskerl, and others. (And, of course, non-Erlang languages … but those guys get enough attention as it is …)

Last but not least, when I was setting up the official LFEX org on Docker Hub, I was pleasantly surprised to see that someone had already pushed up an LFE image, one based on Ubuntu. Nice work, Alexei Sholik!

Setup

This tutorial assumes the following:

  • You are using boot2docker
  • You have Docker installed on a host machine
  • Both are up and running
  • You have exported the Docker environment variables in all the terminal windows you'll be using (2 to 3 is probably all you need)

In order to connect to your containers on your LAN when running boot2docker, you will need to do something like the following:

$ boot2docker ssh -L <HOSTMACHINE>:5099:127.0.0.1:5099

The server on my LAN that's running boot2docker and VirtualBox is 172.16.4.64. So here's the SSH port forwarding setup I ran on 172.16.4.64 in order to have access to my containers from a laptop on the LAN:

$ boot2docker ssh -L 172.16.4.64:5099:127.0.0.1:5099
                        ##        .
                  ## ## ##       ==
               ## ## ## ##      ===
           /""""""""""""""""\___/ ===
      ~~~ {~~ ~~~~ ~~~ ~~~~ ~~ ~ /  ===- ~~~
           \______ o          __/
             \    \        __/
              \____\______/
 _                 _   ____     _            _
| |__   ___   ___ | |_|___ \ __| | ___   ___| | _____ _ __
| '_ \ / _ \ / _ \| __| __) / _` |/ _ \ / __| |/ / _ \ '__|
| |_) | (_) | (_) | |_ / __/ (_| | (_) | (__|   <  __/ |
|_.__/ \___/ \___/ \__|_____\__,_|\___/ \___|_|\_\___|_|
Boot2Docker version 1.3.2, build master : 495c19a - Mon Nov 24 20:40:58 UTC 2014
Docker version 1.3.2, build 39fa2fa
docker@boot2docker:~$

You'll want to leave that window open :-)

And why wouldn't you? Just look at that whale!

Getting the LFE Exchange Docker Image

Assuming you have everything installed and your forwarding is ready to go, let's continue by getting the LFE Docker image:

$ docker pull lfex/lfe

Once it's finished downloading, you can make sure everything's working by running the default command:

$ docker run lfex/lfe
42

This image is dead-simple: it's based on debian:jessie with the standard Erlang package from Debian installed on it (as well as the others needed to support git and rebar). We're working on support for CentOS, Ubuntu, and OpenSUSE as well.

The LFE REPL

Those commands are just executing the default CMD directive provided with the image. We can use this image to run all sorts of commands in the container, such as bash:

$ docker run -t -i lfex/lfe /bin/bash
root@95bc1d88e581:/#

Hey, I've got an idea …

root@95bc1d88e581:/# lfe
Erlang/OTP 17 [erts-6.2] [source] [64-bit] [smp:8:8] [async-threads:10] [kernel-poll:false]

LFE Shell V6.2 (abort with ^G)
> (* 2 (lists:foldl (lambda (n acc) (+ n acc)) 0 (lists:seq 1 6)))
42

While we're in here, let's check out some basic version info:

> (erlang:system_info 'otp_release)
"17"
> (erlang:system_info 'version)
"6.2"
> (erlang:system_info 'driver_version)
"3.1"

Let's quit out:

> ^g
User switch command
 --> q
root@c384176355bd:/# exit
exit

We're no longer running that container, but it still exists:

$ docker ps -a
CONTAINER ID   IMAGE         COMMAND       CREATED    STATUS
0a9b061634b5   f80fa561b172  "/bin/bash"   47 s ago   Exited (0) 12 seconds ago

But you know what? We can do even better than bash … by jumping directly into our favourite REPL :-)

$ docker run -t -i lfex/lfe /usr/bin/lfe
Erlang/OTP 17 [erts-6.2] [source] [64-bit] [smp:8:8] [async-threads:10] [kernel-poll:false]

LFE Shell V6.2 (abort with ^G)
> (* 2 (lists:foldl (lambda (n acc) (+ n acc)) 0 (lists:seq 1 42)))
1806
> ^g
User switch command
 --> q
$

Quitting brought us all the way out, bask to the host machine.

A Simple Customisation of the LFE Dockerfile

So far:

  • We have obtained the LFE image from Docker Hub on our local machine
  • We've run it with the default CMD
  • We've run it with some custom commands

Now we should be comfortable enough using this image to create our own variation, based on it. We'll start simple, thought, with a single change to CMD.

$ mkdir /tmp/lfe
$ cd /tmp/lfe
$ vi Dockerfile

Copy the following into this new file (which is just a change of the original, upstream lfex/lfe Dockerfile from 6 to 42):

FROM lfex/lfe
CMD /usr/bin/lfe -eval "(io:format \"~p~n\"  \
    (list (* 2 (lists:foldl (lambda (n acc) (+ n acc)) 0 (lists:seq 1 42)))))"

Save and quit:

x:

And build your new Docker image:

$ docker build .
...
Removing intermediate container 73cea1afcab1
Successfully built 46957afffb2c

Looking in the output of that last command, we can see that our new image has an ID of 46957afffb2c. Let's tag it (using your own image, of course):

$ docker tag 46957afffb2c crazy42

And run it:

$ docker run crazy42
1806

Excellent – that's the right answer :-)

Let's take a look at our images so far:

$ docker images
REPOSITORY      TAG          IMAGE ID          CREATED             VIRTUAL SIZE
crazy42         latest       46957afffb2c      45 minutes ago      521.9 MB
lfe             latest       e7554d932622      About an hour ago   521.9 MB
lfex/lfe        latest       e7554d932622      About an hour ago   521.9 MB
debian          jessie       aaabd2b41e22      4 weeks ago         154.7 MB

Ready to create another one?

A Simple LFE/YAWS Web App Image

Let's go nuts!

$ mkdir /tmp/sample-app
$ cd /tmp/sample-app
$ vi Dockerfile
FROM lfex/lfe

ENV APP_DIR /opt/sample-app
ENV APP_REPO https://github.com/oubiwann/docker-lfe-yaws-sample-app.git
ENV DEPS_DIR $APP_DIR/deps
ENV YAWS_DIR $DEPS_DIR/yaws
ENV YAWS_APP_ID sampleapp
ENV LFE_DEPS $DEPS_DIR/lutil:$DEPS_DIR/exemplar:$DEPS_DIR/lfest
ENV DEPS $YAWS_DIR:$LFE_DEPS:$DEPS_DIR/ibrowse
ENV ERL_LIBS $ERL_LIBS:/opt/erlang/lfe:$DEPS

RUN apt-get update && apt-get install -y \
        libpam0g-dev

RUN git clone $APP_REPO $APP_DIR && \
        cd $APP_DIR && \
        rebar compile

EXPOSE 5099

CMD sh -c "/opt/sample-app/bin/daemon;while true; do sleep 10; done"
:x
$ docker build .
...
Successfully built 1904cb1d856b

Now we can tag it:

$ docker tag 1904cb1d856b sample-app

And then run it!

$ docker run -d -p 5099:5099 sample-app
1b21f79c42ec84cec841b25ff17e921b4d4ce8ee247c5293d5c0d73766a4c713

Let's make sure that it's running and that our port is exposed:

$ docker ps
CONTAINER ID   IMAGE               COMMAND                STATUS         PORTS
1b21f79c42ec   sample-app:latest   "\"/bin/sh -c 'sh -c   Up 6 seconds   0.0.0.0:5099->5099/tcp

And then open up http://172.16.4.64:5099 (or whatever host you setup for SSH port forwarding) in a web browser. You should be greeted with something that looks like this:

And that's all there is to it!

An LFE Web App Aside

If you'd like to look at the source code for this sample app, it has been made available here:

It takes advantage of two interesting LFE libraries:

  • lfest - a Clojure/Compojure-like macro for defining app routes
  • exemplar - an LFE library for HTML as LFE-native s-expressions

Here are some highlights from the sample app:

Routes

(defroutes
  ('GET "/"
    (sample-app-content:get-sidebar-content arg-data))
  ('GET "/content/:id"
    (sample-app-content:get-content id arg-data))
  ('GET "/relation/:userid/:accountid"
    (sample-app-content:get-content userid accountid arg-data))
  ;; When nothing matches, do this
  ('NOTFOUND
   (let* ((joined-path (++ "/" (string:join path "/")))
          (msg (++ "Unmatched route!~n~n"
                   "Path-info: ~p~n"
                   "joined path: ~p~n"
                   "arg-data: ~p~n~n"))
          (msg-args `(,path ,joined-path ,arg-data)))
    (io:format msg msg-args)
    (sample-app-content:four-oh-four
      (++ (strong "Unmatched Route: ") joined-path)))))

Exemplar Content

(defun get-side-menu ()
  "An example reusable menu."
  (list
    (li (a '(href "/") "Main Page"))
    (li (a '(href "/content/1") "/content/1"))
    (li (a '(href "/content/2") "/content/2"))
    (li (a '(href "/content/3") "/content/3"))
    (li (a '(href "/relation/1/2") "/relation/1/2"))
    (li (a '(href "/bob") "404"))))

Closing

There are soooo many more examples and use cases to explore. Hopefully we'll be putting some of those up on this blog for the benefit and interest of our kind readers.

If you have any questions about the material here, be sure to stop by the LFE mail list and let us know.

Also, you have any any success stories, cool new LFE Docker images, or other amazing tales to share, we want to hear there :-)

See you there!

Author

Duncan McGreggor

Published

07 December 2014

Category

tutorials

Tags