Erlang at Nu Echo

Erlang at Nu EchoSome lessons learned Dominique Boucher Nu Echo

AgendaWho we are, what we doNuGram Hosted ServerWhy ErlangArchitectureSome lessons

Who we are / what we do• Speech applications experts• Lots of R&D• Many tools to support our own practice • Grammar tools • Benchmarking/tuning tools • Testing/monitoring tools

Some of our tools NuBotNuGram IDE

NuGram Hosted Server Hosted infrastructure for deploying and sharing speech grammars – Supports static AND dynamic grammars – Embeds the NuGram technologies • Dynamic grammar instantiation • Grammar conversion to ABNF/GrXML/GSL • Text-based semantic interpretation p• To complement telephony in the cloud (eg. Tropo)

NuGram Hosted ServerComponents – RESTf l API RESTful – www.grammarserver.com/api –C Community website it b it – www.grammarserver.com – NuGram product website – nugram.nuecho.com

NuGram Hosted Server Your application NuGramHosted Server (Java, Ruby, Python, (Java Ruby Python JavaScript, Erlang, etc.) Telephony Platform

NuGram Hosted ServerAn example in Ruby dyngrammar = "#ABNF 1.0 UTF-8; ... " server = GrammarServer.new() session = server.create session("username", "passwrd") server.create_session( username , passwrd ) session.upload("digits2.abnf", dyngrammar); grammar = session.instantiate("digits2.abnf", {}) interpretation = grammar.interpret(one t i t t( two th three f four).to_json ) t j session.disconnect

Why Erlang?• Initial requirements • High-performance HTTP server • Scalability Fault tolerance Scalability, Fault-tolerance • Hot code swapping • Di t ib t d d t b Distributed database• The Erlang appeal • Single language, single platform• Ideal project p j • for experimenting with a different technology

Components OTP • Behaviours for building robust(Open Telecom Platform) Pl tf ) applications Yaws • High performance HTTP Server High-performance • Distributed, fault-tolerant, soft Mnesia realtime DB • Java API to expose Java/Kawa Jinterface code as a regular Erlang node

High-level architecture JInterface JInterface JInterfacewww.grammarserver.com (http + https) Yaws nugram.nuecho.com (http + https) Y RESTful API Mnesia (http + https)

Session handling Java/Kawa Worker Java/Kawa Worker Ja a ead Java Thread Erlang Node SessionMnesia Dispatcher Yaws Request Response

Session handling Java/Kawa Worker Java/Kawa Worker Ja a ead Java Thread Erlang Node Erlang Node cated) cated) SessionMnes (replic Mnes (replic sia sia Dispatcher Dispatcher Yaws Yaws Request Response

Session handling• Sending messages to remote nodes is completely transparent Example ( i lifi d) E l (simplified) Process = db:get session(SessionID) db:get_session(SessionID), Process ! Request.

Session handling• Session timeouts handled by the session process Example E l receive … after Timeout -> db:expire_session(self()) end

Mnesia• Stores Stores… • User accounts • All grammars (templates and instantiated ones) • Node IDs of all Java workers • All session data

What we’ve developedAccount management Registration, email confirmation, etc.BBcode validation & conversion for commentsTwitter widget A process caches the tweets and updates it every 5 minutes Rendering o tweets e de g of ee sRSS reader / widget A process caches the feed content and updates it every hour

What we’ve developedCode-based representation pof the web site structure Tree-like Tree like structure Documents, modules, sectionsSupports the addition on new “modules”Lots of unit tests!

Web site structure-define(SITE_CONFIGURATION, {section, "product_app", "Home", { i d [{module, "welcome", "Welcome - NuGram Platform", {nugram_site, welcome_with_news, []}}, {document, "system_error", "Warning - Request not completed", "system_error.html"}, {section, "nugram_platform", "NuGram Platform", [{document, "overview", "Overview", "nugram_overview.html"}, { {document, "faq", "FAQ", "faq.html"}, , q , , q }, {document, "abnf_tutorial", "Grammar Language Tutorial", "abnf_tutorial.html"}, …

Lessons learned• Erlang strengths • Glueing things together g g g • Data transformations • bbcode XML bbcode, • Protocol handling / processing byte streams • Like encoding detection • G t dynamic d Great d i development environment l t i t • REPL + connecting to a running node

Lessons learned• El Erlang weaknesses k • Sequential computations harder to express • A matter of style • String manipulation g p • Somewhat better now (support for encodings)

Lessons learned• Learn and use OTP from day one • Servers, supervisors, applications • Worth the investment • E Example: t itt feed server l twitter f d • First version without OTP • crashed way too often, making the platform unreliable often • Second version using gen_server

Lessons learned• Dynamically-typed languages make Dynamically typed non-trivial refactorings difficult and error-prone • Not specific to Erlang, but b t a reality lit • Dializer can help• Hot code loading is great • But tricky to do right

Lessons learned• Know your tools • Toolbar, tv, appmon, pman pp ,p• D t reinvent th wheel Dont i t the h l • There are a lot more libraries now • we use Yaws, oauth, smtp_fsm • rebar - great build tool

We learned a lot!And we had a lot of fun()! ()

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Erlang at Nu Echo

by Nu Echo Inc. on May 19, 2011

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