don't call us - we'll push - cross tier push architecture (javaone 2011)
DESCRIPTION
Pushing information is a decoupled and performance effective way to ensure interested parties have the most recent information ASAP.This session looks at reasons and technology for pushing information at various points in an enterprise architecture. Databases can push to the middle tier, the middle tier pushes to the browser and mobile app - triggered by email, chat, JMS message or CEP event and one client can push to another. The link with Event Driven Architecture is explored.HTTP Channels and Web Sockets are demonstrated as well as AJAX based background push, database query result change notification and HTTP calls from the database. We'll look at what to send in an event and how to present the push signal in the end user interface. Attendees will learn how to effectively leverage concepts (such as Bayeux) and technologies to implement push-across-the-tiers in a scalable fashion- thus creating a modern application that satisfies the modern end user.* Introduce push in the real world: don't call us and other examples* Explain how push is good for performance (no polling), for decoupling (consumer does not need to know where the push comes from) and most up-to-date information available (as opposed to polling)* Discuss architecture and all the gaps between and within tier where push may be required and how the trigger can originate* Demonstrate how push can be implemented from a database to the middle tier (for example to refresh cache or send signal that ends up in client)* Demonstrate how push can be implemented from middle tier to client - and what it can be used for* Discussion of presentation/visualization of asynchronous, push-based refresh of client* Leveraging the server-client push, demonstrate how client-client push can be implemented (through client-server AJAX and server-client push)* Demonstrate end-to-end push: database undergoing some DML finally resulting in a browser being refreshed* Linking Push with Event Driven Architecture and Complex Event Processing* Brief future outlookTRANSCRIPT
DON'T CALL US - WE'LL PUSH – ON CROSS TIER PUSH ARCHITECTURE
Lucas Jellema – AMIS (Nieuwegein, The Netherlands)
JavaOne 2011, Birds of a Feather
OVERVIEW
• Asynchronous to the max• Push in enterprise architecture• The harsh reality of push• Web-tier to client
– Browser– Mobile App
• Client to client• Database tier to Business tier• Cross Server Push• Push All the way• The future of push
– Real time
ASYNCHRONOUS COMMUNICATION IN THE REAL WORLD• “I’ll get back to you”• “Don’t call us,…”• Low fuel warning in car• “Please let me know”• “Return to sender – address unknown” • Newspaper delivery• Next instruction from car navigation system• Telephone ringing• Alarm clock buzzing• Parking sensors beeping• Fire alarm screaming
ASYNCHRONOUS INTERACTIONS AND PUSH IN THE IT LANDSCAPE
• More timely information– Notification as soon as possible
• Proactive offering– Do not ask and you shall be given
• Lower load on back end – don’t call us (all the time) …– Stop hitting the F5 button!
• Multi-channel information manipulation and dissemination– Changes and events come in from everywhere
• Decouple system components through generic infrastructure for handling events and push– Yet integrate
PUSHING IT … INTO THE USER INTERFACE• Automatically refreshing (part of) a page
– Update table– Redrawing chart
• Displaying popup to alert user to an event– Arrival of message (email or chat)– Signing in or out of contact (presence)– Lock or release of some resource– Notification
• Changing status of items on the page– Highlight change indicator– Show icon– Change text to italic
• Play a sound
Web Browser
RDBMS
JEE Application Server
Mobile Device
Email Server Chat ServerRDBMS
JEE Application
Server
Web Browser
3 rd party
Mobile Device
Complex Event Processor
NonJava
Server
UPSTREAM NOTIFICATION
• Database to Middle Tier• Middle Tier to Browser
or Mobile device• Browser to other
Browser or Mobile deviceWeb Browser
RDBMS
JEE Application Server
Mobile Device
TYPICAL SERVER-TO-CLIENT PUSH SCENARIO: CHAT
Web Browser
JEE Application Server
AND CLIENT TO SERVER (TO SERVER)
Web Browser
JEE Application Server
THE ‘ONLY TELL WHEN ASKED’ GAME
SERVER PUSH CHALLENGES
• How to push against the ‘one way direction’ and despite limitations– HTTP and JDBC are request/response – not
response only– Browser limit of only two channels to one server
• Server side ‘event handling’– Session has to have an active life beyond
requests• Or requests have a life beyond response
– Higher load on the server– How to handle the (potential) volume of
‘concurrent’ channels and the number of open threads• NIO, Servlet 3.0, Jetty Continuations, Tomcat
Advanced I/O
SERVER PUSH CHALLENGES (2)
• Where do events to push actually come from?– Who perceives/receives (real-time) events (on
the server side)– How are they tied in to the appropriate
sessions?• Client (consumer) side: how to
asynchronously receive events and how to process them/turn them into action and UI updates
• How to correlate an asynchronously received message with a previously sent request or a subscription– For example: mobile phone showing SMS or
WhatsApp messages in a conversation thread style
SERVER TO WEB CLIENT
• AJAX – Asynchronous– Not as asynchronous as you might think
• Reverse AJAX – Comet , Push– Comet implementations
• Streaming – never ending response• Poll• Long Poll• Piggy Back (add push message to normal
response)• Embedded Applet doing raw TCP communications
– Flash with BlazeDS event streaming
• WebSockets
COMET – IMPLEMENTATIONS
• Client side: – many libraries – DOJO is most notable
• most AJAX/JavaScript based• Applets could also be used (via Applet/JS bridge)
• Server Side: – plain servlets, – Servlet 3.0 to alleviate the load on the server
from all the open long-lived requests …– Grizzly (GlassFish)– WebLogic HTTP Channel– GWT?– DWR – Direct Web Remoting– LightStreamer– Jetty– Zie: http://cometdaily.com/maturity.html
DIRECT WEB REMOTING
• Call client side JavaScript functions from Server– In multiple browser sessions– Synchronously as part of request handling– Asynchronously – as server (initiated) push
• Call server side Java methods from the Client– Leading to asynchronous (“background”) AJAX
calls
SERVER PUSH WITH DWR
• DWR configuration:– Servlet in web.xml– WEB-INF/dwr.xml with beans to expose to
JavaScript
Web Browser
JEE Application ServerClock
HTML + JavaScript
CLIENT TO SERVER PUSH TO CLIENT
Web Browser
JEE Application Server
SomeTableWithEventsCoordinator
HTML + JavaScript
Web BrowserHTML + JavaScript
SomeTableWithEventsCoordinator
EventsProcessor
Servlet
THE NUDGE
• Event should have small payload – just an indication of the type of event and a key-reference to the payload
• Based on the information, the consumer decides to retrieve the associated payload, using the keynudge handler
NudgeePayload
Retriever
Nudger
UI Component
WEBSOCKETS
• Protocol – TCP based, initiated with normal HTTP exchange– One more transport option for Comet– Finalized last week!
• Client and Server API– JavaScript (client)– Server side?
• Part of HTML 5– A very loose collection of proposals, concepts and
specifications• Supported in Chrome and Safari as well as
Firefox, …– Also from mobile platform
• Server Side Support very fragmented at this point– With the protocol finalized, server support will
rapidly emerge
Web Browser
JEE Application Server
Mobile Device
Web Browser
Mobile Device
CLIENT TO CLIENT
• Usually really a combination of– Client-to-Server– and Server-to-the-other-Client push
• Exception: Blue Tooth, Near-Field Communication
SERVER TO MOBILE PUSH:MULTIPLEXED, SEMI-POLL BASED
APPLE PUSH NOTIFICATION SERVICE• Persistent TCP/IP connection
– Continuously streaming• TCP/IP connection is initially set up by client
– Passing its identifier to APNS• Server side of applications can send
messages to APNS with the device identifier• APNS streams these messages to the device
– Message payload is JSON
APPLE PUSH NOTIFICATION SERVICE• Using APNS, only one channel is used for all
messages to be pushed to a device– Shared by many different applications
• APNS does store-and-forward (to retain messages when the client is off-line)
• Note: the push payload is very small (< 256 bytes)– just enough for the client to initiate a request for
the real information
ANDROID PUSH NOTIFICATION MULTIPLEXED FROM THE CLOUD
CROSS GAP PUSH MECHANISMS
• Many channels are available to push messages from one entity to another– across application, technology and location
boundaries• JMS (Java/JEE specific) • (one way) WebService (SOAP or REST)• “HTTP Channel”• WebSockets• Http Call to Servlet• XMPP
JMS (JAVA MESSAGE SERVICE) == THE “INTER APPLICATION MAIL MAN”
Application A Application B
JMSQueue
Application C Application X
• JMS is perfect for highly decoupled, scalable, cross JVM/cross server, reliable event push
• JMS is available on any JEE platform• JMS is Java only
– Mobile devices, browsers, databases and .NET do not speak JMS
JMS QUEUE/TOPIC LISTENER
• JMS Listener is notified asynchronously of messages
• Start background job on behalf of web app– Note: spawn thread from Servlet or EJB is not
recommended– Create report, send email, execute batch job
• Listen to events on behalf of web application
– And inform web application of relevant stuffJMS Queue or Topic MDB Web Application
?
EJB
JMS Queue or Topic MDBWeb Application
LIVE VOLLEYBALL REPORTING
JMS Q
ueueBAM
Web Browser
Data Object
Listener (http
channel, JMS, ..)
UI handler
CROSS TIER PUSH – ARCHITECTURE PATTERN
event handler
Scheduled Poll Job
listener listener listener
register
Push Receptor
Payload Retriever
‘Events collector’
THE HOLLYWOOD PRINCIPLE: QUERY RESULTSET CHANGE NOTIFICATION
MIDDLE TIER ALERTED BY DATABASE
SQL query
Register
DatabaseChange
Notification
Oracle RDBMS invokes
Java Listener with event
details
REGISTER DATABASE CHANGE LISTENER
QUERY RESULT CHANGE LISTENER
UPDATE IN DATABASE TRIGGERS NOTIFICATION TO JAVA LISTENER
MULTIPLEXED POLL-BASED DATABASE-TO-MIDDLE TIER PUSH• When no Database Query Result Change
Notification is available – a trick is needed• Some databases can do HTTP calls:
DATABASE TO MIDDLE TIER TO CLIENT NOTIFICATION
Application Scope event handler
HTTP
Proce-dure
servlet
Session cache
EMP
servlet1
2
3 45
6
7
8
9A
D
B
C
Job
DEMO CROSS TIER PUSH – DATABASE MIDDLE TIER BROWSER
MULTIPLEXED POLL-BASED DATABASE-TO-MIDDLE TIER PUSH• A poll based approach can emulate the push
behavior– One thread in the middle tier does polling on behalf
of all sessions: a single channel– A single table in
the database isused to collectall ‘pushable events’
– Middle tier pollretrieves new entries from thetable and publishedevents to centralevent handler
– Listeners registeredwith a centralevent handler
Application Scope event handler
Proce-dure
Scheduled Job
Notifications
session
CD_TBL
sessionsession
FUTURE DEVELOPMENTS
• The real time enterprise• The event driven enterprise• Further evolution of push notification at
every tier– Mobile perhaps leading the way
• Infrastructure and frameworks providing push mechanisms
• Servlet 3.0, Java NIO, WebSockets,SPDY, XMPP and other lighter weight solutions for bi-directional communication over TCP– And broad support in browsers
and application servers– For example: upcoming
WebSockets supportin Glassfish and WebLogic
SUMMARY
• Asynchronous interaction is good for decoupling, decreasing load on system and increasing timeliness
• Push is valuable at various levels and between different components in the enterprise architecture
• Challenges: – push is often against the [http, JDBC,..] grain– correlate push notifications into right consumer– handle asynchronously received push messages– prevent swamping of infrastructure
• Server to client push will gain in scalability and ease– Thanks to WebSockets and implementations thereof
and libraries (e.g. Dojo) leveraging it– Also used for server-to-server and client-to-client
• Push is an essential ingredient of modern applications – from browser and mobile to middle tier and database