DDevelopment & Design

Vert.x on Raspberry Pi

Lightweight JVM web server

Some people say that using Java on Raspberry Pi is a stupid idea. Sure, JVM uses a lot of system resources but when you can watch HD movies on RPi why don’t run a tiny Java app? But I do mean really tiny – no Tomcat nor any other application server involved, no war and deployment stuff. That’s why I came out with idea of using vert.x – a relatively new framework for writing modern web application. In this post I’ll try to show lessons learned after developing a sample app using vert.x and then running it on the Raspberry Pi.

Working with vert.x on RPi

Vert.x is node.js on steroids for JVM. In addition to all the libs for the JVM it offers you a lot more:

  • polyglot – write your application in any language that runs on the JVM (or mix a few)
  • really simple programming model
  • inter-app communication via event bus and shared data
  • ease of scalability and concurrency handling

If you want a gentle start in the world of vert.x I definitely suggest you reading the manual on project website.

Installation

First of all – install Java 8 early access build for ARM from Oracle website. Vert.x indeed requires Java 7, but the 8 build has a real hard float support.

The easiest way to manage vert.x installation is to use GVM:

curl -s get.gvmtool.net | bash
gvm install vertx

Now you should be able to run vertx from the command line.

Development process

In my approach I’m developing the app on my laptop and want to have straight path of running the code on RPI. Since I love the Intellij Idea 12 I put my sources into common maven/gradle structure and use Verticle interface to get full benefits of my IDE: code completion, refactoring and testing support. I use Groovy as a language for my verticles but I want the sources to be compiled on my laptop instead of RPI which a bit improves startup time of the app.

The examples for vert.x distribution are not reaaly development-friendly but I’ve found great example of Groovy starter project on GitHub which introduces two huge ideas: separating configuration of the app in single JSON file and a runVertx gradle task to build and run the app in a single step. I also use the web-server vert.x module to serve static web files of the app frontend. So I have SockJS and REST verticles in the backend and JavaScript frontend in a single project root.

Here is the final layout explained:

src/main/groovy - verticles code
    App.groovy - app lancher
src/main/test - verticles tests
web - frontend stuff
build.gradle - gradle script with runVertx task
run.sh - script for running app on RPI (no compilation)

And a typical development process looks like this:

  • write verticles code (*)
  • write unit tests for verticles (*)
  • run the app on laptop and modify the frontend
  • copy binaries to RPi and run the app from command line

(*) change the order of these two for TDD ;)

The only thing I’m only struggling from is lack of runtime reloading of verticles. Maybe using JRebel could help there but I ain’t got the licence (yet).

You can see my example project here.

Benchmark

I also did some benchmarking of vert.x app on RPI throughput. Sure, you cannot expect that single RPI could handle a lot of transactions per sec, so the test was just for fun. In the test I served a static CSS (bootstrap) and invoked a really simple REST resource (example details/Joe/123 mapping from RouteMatcher). I used siege with 2 and 200 consumers and compared the results between the very.x (1 instance), node.js express and nginx (just for static CSS). I installed node.js 0.8.18 from binaries found here.

  • It is nice that serving static files is quite as fast as in the nginx. There is a benchmark showing that Monkey web server is a bit faster, but in my environment I wasn’t able to achieve more than 45 req/sec on nginx, so ~40 req/sec on vert.x is really good result.
  • Vert.x seems to be about 2-2.5 times faster than node.js with express. This is similar to Tim Fox’ benchmark with both node.js and vert.x in single instance. (BTW: I have no idea how to get 30k req/sec on a workstation as in Tim’s test).
  • The benchmark shows that RPi is indeed a toy PC – on my workstation it’s really easy to achieve thousands of requests per second. So forget about handling hundreds of requests per seconds on a single RPi instance.

(a bit) Speeding up startup time

The thing that really puts node.js in front is the startup time. Java is slow at both JVM startup and while classloading. My first application deployed on RPi took about 30 sec to start, while on my laptop it was about 2-3 seconds. It is possible to cut it down to 18 seconds, here are a few hints:

  • don’t compile sources directly on RPi – build a jar on your workstation. In my setup I run the server from gradle on my laptop but also have a bash script to run it on raspberry which passes vert.x a -cp parameter pointing to builded jar.
  • don’t run a SockJS server when not needed. It tooks about 5 sec to start. You can disable it by setting bridge to false in mod-web configuration.
  • you can write your own mod-web in just a few lines of code. You will save some milliseconds but also this setup allows you to pass custom RESTful routes to RouteMatcher. Look at this example:
def rm = new RouteMatcher()
rm.get('/details/:user/:id', { HttpServerRequest req ->
    req.response.end "User: ${req.params()['user']} ID: ${req.params()['id']}"
} as Handler<HttpServerRequest>)

// Catch / - serve the index page
rm.get('/', { HttpServerRequest req ->
    req.response.sendFile("web/index.html")
} as Handler<HttpServerRequest>)

// Catch all - just send the file from web directory
rm.getWithRegEx('.*', { HttpServerRequest req ->
    req.response.sendFile "web/${req.path}"
} as Handler<HttpServerRequest>)

To debug the most time consuming steps on app startup, you should configure log4j logging. Vert.x outputs some info about deploying verticles, you can also put your own logging messages. Just copy log4j.jar to vert.x lib directory and add

-Dorg.vertx.logger-delegate-factory-class-name=org.vertx.java.core.logging.impl.Log4jLogDelegateFactory

parameter in vert.x startup script.

Sample project

You can check these concepts by cloning a top monitor GitHub project. It is a Dashing-inspired web app showing results from calling a top command by lucid JQuery knobs.
Every 2 seconds stats from the top call are pushed through eventBus (and internally by SockJS) to frontend.

The project itself it not smashing, you can just check the structure and the tests when I’m mocking ARM-specific top command results. Enjoy!

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DDevelopment & Design

Clojure web development – state of the art

It’s now more than a year that I’m getting familiar with Clojure and the more I dive into it, the more it becomes the language. Once you defeat the “parentheses fear”, everything else just makes the difference: tooling, community, good engineering practices. So it’s now time for me to convince others. In this post I’ll try to walktrough a simple web application from scratch to show key tools and libraries used to develop with Clojure in late 2015.

Note for Clojurians: This material is rather elementary and may be useful for you if you already know Clojure a bit but never did anything bigger than hello world application.

Note for Java developers: This material shows how to replace Spring, Angular, grunt, live-reload with a bunch of Clojure tools and libraries and a bit of code.

The repo with final code and individual steps is here.

Bootstrap

I think all agreed that component is the industry standard for managing lifecycle of Clojure applications. If you are a Java developer you may think of it as a Spring (DI) replacement - you declare dependencies between “components” which are resolved on “system” startup. So you just say “my component needs a repository/database pool” and component library “injects” it for you.

To keep things simple I like to start with duct web app template. It’s a nice starter component application following the 12-factor philosophy. So let’s start with it:

lein new duct clojure-web-app +example

The +example parameter tells duct to create an example endpoint with HTTP routes - this would be helpful. To finish bootstraping run lein setup inside clojure-web-app directory.

Ok, let’s dive into the code. Component and injection related code should be in system.clj file:

(defn new-system [config]
  (let [config (meta-merge base-config config)]
    (-> (component/system-map
         :app  (handler-component (:app config))
         :http (jetty-server (:http config))
         :example (endpoint-component example-endpoint))
        (component/system-using
         {:http [:app]
          :app  [:example]
          :example []}))))

In the first section you instantiate components without dependencies, which are resolved in the second section. So in this example, “http” component (server) requires “app” (application abstraction), which in turn is injected with “example” (actual routes). If your component needs others, you just can get then by names (precisely: by Clojure keywords).

To start the system you must fire a REPL - interactive environment running within context of your application:

lein repl

After seeing prompt type (go). Application should start, you can visit http://localhost:3000 to see some example page.

A huge benefit of using component approach is that you get fully reloadable application. When you change literally anything - configuration, endpoints, implementation, you can just type (reset) in REPL and your application is up-to-date with the code. It’s a feature of the language, no JRebel, Spring-reloaded needed.

Adding REST endpoint

Ok, in the next step let’s add some basic REST endpoint returning JSON. We need to add 2 dependencies in project.clj file:

:dependencies
 ...
  [ring/ring-json "0.3.1"]
  [cheshire "5.1.1"]

Ring-json adds support for JSON for your routes (in ring it’s called middleware) and cheshire is Clojure JSON parser (like Jackson in Java). Modifying project dependencies if one of the few tasks that require restarting the REPL, so hit CTRL-C and type lein repl again.

To configure JSON middleware we have to add wrap-json-body and wrap-json-response just before wrap-defaults in system.clj:

(:require 
 ...
 [ring.middleware.json :refer [wrap-json-body wrap-json-response]])

(def base-config
   {:app {:middleware [[wrap-not-found :not-found]
                      [wrap-json-body {:keywords? true}]
                      [wrap-json-response]
                      [wrap-defaults :defaults]]

And finally, in endpoint/example.clj we must add some route with JSON response:

(:require 
 ...
 [ring.util.response :refer [response]]))

(defn example-endpoint [config]
  (routes
    (GET "/hello" [] (response {:hello "world"}))
    ...

Reload app with (reset) in REPL and test new route with curl:

curl -v http://localhost:3000/hello

< HTTP/1.1 200 OK
< Date: Tue, 15 Sep 2015 21:17:37 GMT
< Content-Type: application/json; charset=utf-8
< Set-Cookie: ring-session=37c337fb-6bbc-4e65-a060-1997718d03e0;Path=/;HttpOnly
< X-XSS-Protection: 1; mode=block
< X-Frame-Options: SAMEORIGIN
< X-Content-Type-Options: nosniff
< Content-Length: 151
* Server Jetty(9.2.10.v20150310) is not blacklisted
< Server: Jetty(9.2.10.v20150310)
<
* Connection #0 to host localhost left intact
{"hello": "world"}

It works! In case of any problems you can find working version in this commit.

Adding frontend with figwheel

Coding backend in Clojure is great, but what about the frontend? As you may already know, Clojure could be compiled not only to JVM bytecode, but also to Javascript. This may sound familiar if you used e.g. Coffescript. But ClojureScript philosophy is not only to provide some syntax sugar, but improve your development cycle with great tooling and fully interactive development. Let’s see how to achieve it.

The best way to introduce ClojureScript to a project is figweel. First let’s add fighweel plugin and configuration to project.clj:

:plugins
   ...
   [lein-figwheel "0.3.9"]

And cljsbuild configuration:

:cljsbuild
    {:builds [{:id "dev"
               :source-paths ["src-cljs"]
               :figwheel true
               :compiler {:main       "clojure-web-app.core"
                          :asset-path "js/out"
                          :output-to  "resources/public/js/clojure-web-app.js"
                          :output-dir "resources/public/js/out"}}]}

In short this tells ClojureScript compiler to take sources from src-cljs with figweel support and but resulting JavaScript into resources/public/js/clojure-web-app.js file. So we need to include this file in a simple HTML page:

<!DOCTYPE html>
<head>
</head>
<body>
  <div id="main">
  </div>
  <script src="js/clojure-web-app.js" type="text/javascript"></script>
</body>
</html>

To serve this static file we need to change some defaults and add corresponding route. In system.clj change api-defaults to site-defaults both in require section and base-config function. In example.clj add following route:

(GET "/" [] (io/resource "public/index.html")

Again (reset) in REPL window should reload everything.

But where is our ClojureScript source file? Let’s create file core.cljs in src-cljs/clojure-web-app directory:

(ns ^:figwheel-always clojure-web-app.core)

(enable-console-print!)

(println "hello from clojurescript")

Open another terminal and run lein fighweel. It should compile ClojureScript and print ‘Prompt will show when figwheel connects to your application’. Open http://localhost:3000. Fighweel window should prompt:

To quit, type: :cljs/quit
cljs.user=>

Type (js/alert "hello"). Boom! If everything worked you should see and alert in your browser. Open developers console in your browser. You should see hello from clojurescript printed on the console. Change it in core.cljs to (println "fighweel rocks") and save the file. Without reloading the page your should see updated message. Figweel rocks! Again, in case of any problems, refer to this commit.

In the next post I’ll show how to fetch data from MongoDB, serve it with REST to the broser and write ReactJs/Om components to render it. Stay tuned!

DDevelopment & Design

Apache HISE + Apache Camel

Check out this SlideShare Presentation: Apache HISE + Apache CamelView more presentations from Rafal Rusin.Check out this SlideShare Presentation: Apache HISE + Apache CamelView more presentations from Rafal Rusin.