Zing Me Real Time Web Chat Architect

1. Zing Me Web Chat Architect
By Chau Nguyen Nhat Thanh
ZingMe Technical Manager
Web Technical - VNG

2. Agenda
●
About Zing Me
●
Zing Me platform strategy
●
Zing Me web chat architect
●
Problem with real time message in HTTP
●
Connection server
●
Message server
●
Online server
●
Some statistic information
2

3. About Zing Me

4. SNS Platform

5. Updated stats
● 45M registered accounts
● 2.2M daily active users
● 7M monthly active users
● > 500 servers (2 K cores)
● 70 DB servers, >60 Memcached servers
● ~ 150 Web servers
● 40 servers for Hadoop farm
● Others (storage, ...)

6. Zing Me Technology
● Load balancing: HA proxy, LVS
● Web server: Nginx, Lighttpd
● Web caching: Squid, Varnish
● Caching: Redis, Memcached, Membase
● CDN: in progress
● Programming language: PHP, C++,Java, Python,
Bash script, Erlang
● Searching: Solr, Lucene
● DB: MySQL , Cassandra, HBase
● Log system: Scriber + Hadoop

7. Zing Me platform strategy
● Open platform
● Open Social API
● Open Auth
● Zing Connect
● http://open.me.zing.vn/
● Open service
● Cloud Memcache
● Cloud Key Value Storage
● Virtualization for Hosting Service

8. Zing Me platform strategy
● Focus on communication tools:
● Email: Zing mail
● Private message
● IM : ZingMe Web Chat
● Notification: Zing Notification System

9. Zing Me Web Chat
Architect

10. Frontend UI

11. Problem with realtime message
● Realtime message in HTTP
● Browser actively connect to web server
● How can web server push the new message to the
browser ?
● COMET is the answer
● COMET overview
● Comet is a web application model in which a long-held
HTTP request allows a web server to push data to a
browser, without the browser explicitly requesting it
(wikipedia)
● Implementation: hiden iframe, ajax long-polling, script
tag long polling

12. Frontend JS
● 2 developers in 4 months
● Building from the scratch based on
zmCore.js, a Zing Me homemade js
framework
● Using long-polling for pushing new messge
● Get online friend list
● Get last message
● Verify session

13. Backend
● Must scalable
● Handle large number of connetions
● Connection server handles the long-polling
connection
● Friend Online server keeps track online friends
● Message Server stores the messages
● Message Delivery Worker transfers messages from
the Message Server to Connection Server
● Channel Server maps the users with their
connections

14. Web Chat Architect Overview

15. Connection Server
● Must handle large number of concurrent
connections ( > 100K connections)
● Implement in C++
● Using native EPOLL system call
● NONBLOCKING mode for async IO
● Dev in 8 months

16. Connection Server
Implementation
● Long polling

17. Connection Server
Implementation
● Keep connections until message come or
timeout
● Server must keep a large number of
connections (C100K)
● Use the same solution like memcached,
haproxy

18. Connection Server
Implementation
● Why EPOLL?
● General way to implement tcp servers is “one
thread/process per connection”. But on high
loads this approach can be not so efficient and
we need to use another patterns of connection
handling.(kovyri.net)
● Need an asynchronous way
● EPOLL is the solution

19. Connection Server
Implementation
● Coding with EPOLL
● Create specific file descriptor for epoll calls:
epfd = epoll_create(EPOLL_QUEUE_LEN);
● After first step you can add your descriptors to epoll with following call:
static struct epoll_event ev;
int client_sock;
...
ev.events = EPOLLIN | EPOLLPRI | EPOLLERR | EPOLLHUP;
ev.data.fd = client_sock;
int res = epoll_ctl(epfd, EPOLL_CTL_ADD, client_sock, &ev);

20. Connection Server
Implementation
● When all your descriptors will be added to epoll, your process can idle and wait to
something to do with epoll’ed sockets:
while (1) {
// wait for something to do...
int nfds = epoll_wait(epfd, events,
MAX_EPOLL_EVENTS_PER_RUN,
EPOLL_RUN_TIMEOUT);
if (nfds < 0) die("Error in epoll_wait!");
// for each ready socket
for(int i = 0; i < nfds; i++) {
int fd = events[i].data.fd;
handle_io_on_socket(fd);
}
}

21. Friend Online Server
● Hard to scale
● Implement in C++
● Using some cheats to define user online
● Caching is hard
● Dev in 1 month

22. Message Server
● Store the messages
● Implement in Java
● Problem with memory usage
● C++ version in progress
● Notify new message by queue
● Worker will deliver message to user by
connection server

23. Web Chat statistic

24. Total message

25. Hourly stats

26. Q&A
Contact info:
Chau Nguyen Nhat Thanh
thanhcnn@vng.com.vn
me.zing.vn/thanhcnn2000