Simone Bordet gave a presentation on CometD, a web messaging framework that implements a publish/subscribe pattern for web applications. CometD allows for server push capabilities and is cloud-ready, either being stateless or easily clusterable. Simone discussed several use cases for CometD including social networking, chat, online gaming, auctions/trading, and systems monitoring. Key features of CometD were also summarized, including its JavaScript and server-side libraries, performance, clustering capabilities, and support for cloud environments.

1. Simone Bordet
sbordet@intalio.com
Cloud-Ready
Web Messagging
with CometD
CloudConf – Torino
April 3rd, 2014

2. Simone Bordet
sbordet@intalio.com
Who Am I
 Simone Bordet
 sbordet@intalio.com
 @simonebordet
 Open Source Contributor
 Jetty, CometD, MX4J, Foxtrot, LiveTribe, JBoss, Larex
 Lead Architect at Intalio/Webtide
 Jetty's SPDY, FastCGI and HTTP client maintainer
 CometD project leader
 Web messaging framework

3. Simone Bordet
sbordet@intalio.com
Agenda
 What is CometD ?
 CometD Use Cases
 CometD Features
 Questions & Answers

4. Simone Bordet
sbordet@intalio.com
What is CometD ?

5. Simone Bordet
sbordet@intalio.com
What is CometD
 CometD is a web messaging framework
 Implements a publish/subscribe pattern on the web
 Web applications use a request/response paradigm
 Because historically web applications run over HTTP
 CometD uses a messaging paradigm
 For example: 1 “request” message, 3 “response” messages
 Server push – no “request”, 1-N “response” messages
 Cloud-ready
 Either stateless or easily clusterable

6. Simone Bordet
sbordet@intalio.com
CometD Use Cases

7. Simone Bordet
sbordet@intalio.com
CometD Use Cases
 Social Networking
 Chat and Notifications

8. Simone Bordet
sbordet@intalio.com
CometD Use Cases
 Online Gaming
 Not First Person Shooters – yet :)

9. Simone Bordet
sbordet@intalio.com
CometD Use Cases
 Auctions & Trading
 Updating bids, prices and availability

10. Simone Bordet
sbordet@intalio.com
CometD Use Cases
 Systems Monitoring
 Alerts and System Status

11. Simone Bordet
sbordet@intalio.com
CometD Use Cases
 Online Collaboration/Productivity Tools

12. Simone Bordet
sbordet@intalio.com
Comet Web Applications
 A new kind of web applications
 Server-side event driven
 Highly dynamic using AJAX / WebSocket on the client
 Asynchronous and concurrent by definition
 Big impacts on servers
 Servers must support async I/O
 Thread-per-request model does not scale
 Servers must support WebSocket
 With an easy fall-back to HTTP

13. Simone Bordet
sbordet@intalio.com
CometD Overview

14. Simone Bordet
sbordet@intalio.com
CometD Features
 CometD provides libraries
 Build your own solutions with the CometD libraries
 No out of the box products
 CometD JavaScript Libraries
 CometD Java Libraries

15. Simone Bordet
sbordet@intalio.com
CometD Performance
 CometD Load Test (using a real chat application)
 HTTP
 20k clients
 50k messages/s
 200 ms median latency
 WebSocket
 100k clients
 50k messages/s
 4 ms median latency

16. Simone Bordet
sbordet@intalio.com
CometD Performance
 CometD 3
 Roughly 25% to 100% better than CometD 2
 Depending on the load
 CometD 3 based on Servlet 3.1
 Ships new HTTP transport based on Servlet 3.1 Async I/O
 Jetty 9.1 implements Servlet 3.1
 Implementation already very stable

17. Simone Bordet
sbordet@intalio.com
CometD Features

18. Simone Bordet
sbordet@intalio.com
CometD Features – JavaScript
require(['dojox/cometd', 'dojo/domReady!'],
function(cometd) {
cometd.init('http://myserver/cometd');
cometd.subscribe('/my/channel', function(message) {
var data = message.data;
// Do something with the data
});
cometd.publish('/my/channel', {
chatText: 'hello!'
});
cometd.disconnect();
});

19. Simone Bordet
sbordet@intalio.com
CometD Features – JavaScript
 Easy to make Comet “Hello Worlds”
 Very difficult to make it fail nicely in real scenarios –
CometD does it
 Network disconnection detection
 Applications notified via function callback
 Message batching
 Sending multiple messages to server efficiently
 Page reload extension
 Reload a page in the browser without losing connectivity

20. Simone Bordet
sbordet@intalio.com
CometD Features – Server
 Spring Framework integration
 Confidentiality
 HTTPS and WSS supported out of the box
 Authentication
 Controlled via SecurityPolicy
 OAuth integration
 Authorization
 Coarse grained via SecurityPolicy
 Fine grained via channel Authorizers

21. Simone Bordet
sbordet@intalio.com
CometD Features – Server
 Transport independence (both client and server)
 Applications do not hardcode to a specific transport
 Lazy messages
 Deliver non important messages on first occasion
 Save I/O and CPU when it matters
 Acknowledge Extension
 Provides server-to-client ordering and acknowledgement of
messages
 Activity Extension
 Disconnect idle clients after a period of inactivity

22. Simone Bordet
sbordet@intalio.com
CometD Cloud Features

23. Simone Bordet
sbordet@intalio.com
CometD Cloud Features
 The Cloud:
 Dynamic horizontal scaling under load
 Various degrees of support for fail-over
 Almost always requires application support
 Applications have to be aware of multiple nodes
 Data sharing / replication

24. Simone Bordet
sbordet@intalio.com
CometD Features – Clustering
 Oort
 CometD's scalability clustering solution
 Shards clients among nodes
 Not a high availability solution
 On node failure clients reconnect automatically
 But may have lost information
 Oort cluster members autodiscovery
 Multicast based
 Static based on “well known” nodes
 Existing nodes forward topology to new nodes

25. Simone Bordet
sbordet@intalio.com
CometD Features – Clustering

26. Simone Bordet
sbordet@intalio.com
CometD Features – Oort
 Oort cluster messages auto re-broadcasting
 For example, chat applications work out of the box
 No code needed !
B
A C
Client A Client B Client C

27. Simone Bordet
sbordet@intalio.com
CometD Features – Seti
 Seti
 Clustered peer-to-peer communication
 Oort performs broadcasting communication
 Seti maps a user ID token to a session ID
 Presence information is broadcasted on the cluster
 Each Seti knows the location of all user IDs
 Efficient peer-to-peer communication
 Multiple session IDs for the same user ID
 For example, connecting from desktop and mobile

28. Simone Bordet
sbordet@intalio.com
CometD Features – Seti
B
A C
Client A Client B Client C

29. Simone Bordet
sbordet@intalio.com
CometD Features – OortObjects
 Distributed OortObjects
 Distribution of object state across nodes
 OortObject<T>
 A composite, uniquely named, object made of “parts”
 Only one “part” is owned by the node, others are read-only
 Trades more memory for smaller data access latency
 Typical Examples
 The number of users on each node
 The list of chat rooms a friend has joined
 The friends of a friend in a social application

30. Simone Bordet
sbordet@intalio.com
CometD Features – OortObjects
A1, A2
B1
NodeA
C1A C2A
users
A1, A2
B1
NodeB
C1B
users

31. Simone Bordet
sbordet@intalio.com
CometD Features – OortServices
 Distributed OortServices
 Forwarding of service actions across nodes
 OortService<R, C>
 One uniquely named service in each node
 Forwards actions to owner node (possibly itself)
 Trades less memory for higher data access latencies
 Typical Examples
 Precise counters (even unique-across-cluster)
 Update actions (e.g. chess moves)

32. Simone Bordet
sbordet@intalio.com
CometD Features – OortServices
NodeA
P1
game_service
forward(...)
NodeB
P2
game_service
onForward(...)
onForwardSucceeded(...)

33. Simone Bordet
sbordet@intalio.com
CometD Features – OortObjects
 OortObject and OortService allow sharding
 Geographical-based, load-based, business-based
 Typical examples
 US users vs EU users
 Play games locally for better performance

34. Simone Bordet
sbordet@intalio.com
Questions
&
Answers

35. Simone Bordet
sbordet@intalio.com
References
 CometD
 http://cometd.org
 http://docs.cometd.org
 Jetty
 http://eclipse.org/jetty
 Intalio/Webtide
 https://webtide.com