This document discusses scalable architectures and provides an overview of load balancing, web servers, and database servers. It begins with an introduction to load balancing options like software-based solutions (HAProxy, Pound, Varnish) and hardware appliances. It then covers setting up multiple web servers and load balancing between them, as well as database replication and partitioning strategies to scale databases. The goal is to help applications grow from a single server to distributed, scalable architectures.

1. Scalable
Architectures 101
ConFoo
Mar 10, 2011
Mike Willbanks
Blog: http://blog.digitalstruct.com
Twitter: mwillbanks
IRC: lubs on freenode

2. Who am I?
● Software Development Manager
● Organizer of MNPHP / MNMySQL
● Zend Certified Engineer (PHP/ZF)

3. Scalability?
Your application is growing, your systems are slowing
and growth is inevitable...
● Where do we go from here?
● Load Balancing ● Job Servers
● Web Servers ● DNS Servers
● CDN Servers
● Database Servers
● Cache Servers ● Front­End Performance

4. The Beginning
Single Server Syndrome
● One Server Many Functions
● Web Server, Database Server, Cache Server, Job
Server, DNS Server, Mail Server....
● How we know it's time
● iostat, cpu load, overall degradation
● OR.....

6. The Next Step
Single Separation Syndrome
● Separation of Web and Database
● Fix the main disk I/O bottleneck.
● Still generally running several things on a single
server.

7. Uh, oh :(

8. Load Balancing

9. A Load Balanced Environment

10. Load Balancing Options
● DNS Rotation (Little to No Cost)
● Not reliable, but it can work on a small scale.
● Software Based (Commodity Server Cost)
● HAProxy, Pound, Varnish, Squid, Wackamole,
Perlbal, Web Server Proxy (Nginx, Apache, etc)...
● Hardware Based (High Cost Appliance)
● Several vendors ranging based on need.
– A10, F5, etc.

11. Load Balancing Routing Types
● Round Robin ● URI
● Static ● URI Parameter
● Least Connections ● Header
● Source ● Cookie
● IP ● Regular Expression
● Basic Authentication

12. Targeting Open Source Software Packages
● Out of the many options we will focus in on 3
● HAProxy – By and large one of the most popular.
● Pound – Said to be great for medium traffic sites.
● Varnish – A caching solution that also does load
balancing

13. HAProxy
● Pros
● Extremely full featured
● Very well known
● Handles just about every type of routing
● Several examples online
● Has a web­based GUI
● Cons
● No native SSL support (use Stunnel)
● Setup can be complex and take a lot of time

14. HAProxy: Sample Configuration
global listen localhost 0.0.0.0:80
log 127.0.0.1 local0 option httpchk GET /
log 127.0.0.1 local1 notice balance roundrobin
maxconn 4096 cookie SERVERID
user haproxy server serv1 0.0.0.0:8080 check
group haproxy inter 2000 rise 2 fall 5
daemon server serv2 0.0.0.0:8080 check
inter 2000 rise 2 fall 5
defaults option httpclose
log global stats enable
mode http stats uri /lb?stats
option httplog stats realm haproxy
option dontlognull stats auth test:test
retries 3
option redispatch
maxconn 2000
contimeout 5000
clitimeout 50000
srvtimeout 50000

15. Pound
● Pros
● chroot support
● Native SSL support
● Insanely simple setup
● Supports virtually all types of routing
● Many online tutorials
● Cons
● No web­based statistics (use poundctl)
● HAProxy can scale more...

16. Pound: Sample Configuration
User "www-data"
Group "www-data"
LogLevel 1
Alive 30
Control "/var/run/pound/poundctl.socket"
ListenHTTP
Address 127.0.0.1
Port 80
xHTTP 0
Service
BackEnd
Address 127.0.0.1
Port 8080
End
BackEnd
Address 127.0.0.1
Port 8080
End
End
End

17. Varnish
● Pros
● Supports front­end caching
● Farily simple setup
● Extremely well known
● Many online tutorials
● Large suite of tools (varnishstat, varnishtop,
varnishlog, varnishreplay, varnishncsa)
● Cons
● No native SSL support (use Pound or Stunnel)
● If you want a WebGUI you must PAY

18. Varnish: Sample Configuration
backend default1 { director default round-robin {
.host = "127.0.0.1"; {
.port = "8080"; .backend = default1;
.probe = { }
.url = "/"; {
.interval = 5s; .backend = default2;
.timeout = 1s; }
.window = 5; }
.threshold = 3;
} sub vcl_recv {
} if (req.http.host ~ "^127.0.0.1$") {
set req.backend = default;
backend default2 { }
.host = "127.0.0.1"; }
.port = "8080";
.probe = {
.url = "/";
.interval = 5s;
.timeout = 1s;
.window = 5;
.threshold = 3;
}
}

19. Load Balancing: Keep in Mind
● Web Servers
● One always needs to be available
● Don't use SSL on the web server level!
● Headers
● Pass headers if SSL is on or not
● Client IP is likely on X­forwarded­for
● If using Virtual Hosts pass the Host
● Sessions
● Need a solution if not using sticky routing

20. Web Servers

21. Many Web Servers
● Apache
● IIS
● Nginx
● Lighttpd
● etc.

22. Web Server Configuration
● Sever name should be the same on all servers
● Make a server alias so you can reach individual
servers w/o load balancing
● Each configuration SHOULD or MUST be the
same.
● Client IP generally is in X­forwarded­for.
● SSL will not be in $_SERVER['HTTPS'] and
HTTP_ header instead.

23. Web Servers: Keep in Mind
● Files
● All web servers need our files.
● Static content could be tagged in version control.
● Static content may need a file server / CDN / etc.
● User Generated content on NFS mount or served
from the cloud or a CDN.
● Sessions
● All web servers need access to our sessions.
● Remember disk is slow and the database will be a
bottleneck. How about distributed caching?

24. Web Servers: Other Information
● Running PHP on your web server may be a
resource hog, you may want to offload static
content requests to varnish, nginx, lighttpd or
some other lightweight web server.
● Running a proxy to your main web servers works
great for hardworking processes. While serving
static content from the lightweight server.

25. Database
Servers

26. Single Database Server
Single Database Server
● Lots of options and steps as we move forward.

27. Database Replication
Single Master, Single Slave
● Write code that can write to the master and read from
the slave.
● Exception: Be smart, don't write to the master and
read from the slave on the table you just wrote to.

28. Database Replication Multiple Slaves
Single Master, Multiple Slaves
● It is a great time to start to implement connection
pooling.

29. Database Replication Multiple Everything
Multiple Master, Multiple Slaves
● Do NOT write to both masters at once with MySQL!
● Be warned, auto­incrementing now should change so
you do not conflict.

30. Database Table Partitioning
Segmenting your Data
● Vertical Partitioning
● Move less accessed columns, large data columns
and columns not likely in the where to other tables.
● Horizontal Partitioning
● Done by moving rows into different tables.
– Based on Range, Date, User or Interlaced
– May require duplicate lookup tables for different
indexes.

31. Database Servers: Keep in Mind
● Replication
● There may be a lag!
● All reports / read queries should go here
● Don't read here directly after a write
– Transactions / Lag / etc.
● Sessions
● Never store sessions in the DB
– Large binlogs, garbage collection causes slow queries,
queue may fill up and cause a crash or max connections.

32. Cache
Servers
(not full page)

33. Cache Servers: What Type?
“Caching is imperative in scaling and performance”
● Single Server
– Shared Memory: APC / Xcache / etc
– File Based: Files / Sqlite / etc
– Not highly scalable, great for configuration files.
● Distributed
– Memcached, Redis, etc.
– Setup consistent hashing.
● Do not cache what cannot be re­created.

34. Caching: Single Server
In The Beginning
● Single Caching Server
● Start to cache fetches, invalidate cache on write and
write new cache, always reading from the cache.

35. Caching: Going Distributed
Distributed Mania
● Write based on consistent hashing (hash of a key that
you are writing)
● Server depends on the hash.
● Hint – use the memcached pecl extension.

36. Caching: Read / Write with a Database
In the most simple form...

37. Caching: Keep in Mind
● Replicated or not...
● Elasticity
● Consistent hashing – cannot add or remove w/o losing data
● Sessions
● Store me here... please please please!
● Memory Caches
● Durability ­ If it fails, it's gone!
● Ensure dedicated memory!
● If you run out of memory, does it remove an old and add the
new or not allow anything to come in?

38. Job
Servers
(message queues)

39. “Message queues and mailboxes are software­engineering
components used for interprocess communication, or for inter­
thread communication within the same process. They use a queue
for messaging – the passing of control or of content.”
http://en.wikipedia.org/wiki/Message_queue

40. Messages: They're Everywhere

41. Message Queues: What are They?
● A FIFO buffer
● Asynchronous push / pull
● An application framework for sending and
receiving messages.
● A way to communicate between applications /
systems.
● A way to decouple components.
● A way to offload work.

42. Message Queues: The Basic Concept
Single Job Server
Producer Message Queue Consumer
Queue Receive
Server
● Lots of options and steps as we move forward.

43. Message Queue: Going Distributed
Distributed Mania
Producer Producer Producer
Queue Queue Queue
Server Server Server
Consumer Consumer Consumer Consumer Consumer
● Load balance a message queue for scale
● Can continue to create more workers

44. Message Queues: Useful for?
● Asynchronous Processing
● Communication between Applications / Systems
● Image Resizing
● Video Processing
● Sending out Emails
● Auto­Scaling Virtual Instances
● Log Analysis
● The list goes on...

45. Message Queues: Keep in Mind
● Replication or not?
● You need to keep your workers running
● Supervisord or monit or some other monitoring...
● Don't offload things just to offload
● If it needs to be real­time and not near real­time this
is not a good place for things – however, your boss
does not need to know :)

46. DNS Servers

47. DNS Servers: Are you running your own?
● Just about every domain registrar runs DNS
● If you don't need to, do not run your own.
● Anycast DNS
● Anycast is a network addressing and routing
scheme whereby data is routed to the "nearest" or
"best" destination as viewed by the routing topology.
● It's sexy, it's sweet and it is FAST!

48. DNS Servers: Identifying a Good Service
● Wildcard support
● Failover / Distributed
● CNAME support
● TXT support
● Name Server support

49. CDN Servers

50. CDN: What is a CDN?
● A content delivery network or content distribution network
(CDN) is a system of computers containing copies of data,
placed at various points in a network so as to maximize
bandwidth for access to the data from clients throughout
the network. A client accesses a copy of the data near to
the client, as opposed to all clients accessing the same
central server, so as to avoid bottlenecks near that server.
● Content types include web objects, downloadable objects
(media files, software, documents), applications, real time
media streams, and other components of internet delivery
(DNS, routes, and database queries).
http://en.wikipedia.org/wiki/Content_delivery_network

51. CDN: Why Use One?
● Extremely fast at serving files
● Increased serving capacity
● Distributed nodes
● Frees up your server for the difficult stuff

52. CDN: The Types
● Origin Pull
● Utilizes your own web server and pulls the content
and stores it in their nodes.
● PoP Pull
● You upload the content to something like S3 and it
has a CDN on the top of it like CloudFront.

53. CDN: What Should I Use?
● Depends on your need...
● Origin Pull is great if you want to maintain all of
the content in your web server.
● PoP Push is great for storing things like user
generated content.

54. Mail Servers

55. Mail Servers: A Quick Note
● Google Apps – just offload it!
● If you do not need to run a mail server don't.
● SpamAssassin and ClamAV are resource hogs
● If you need it, put it on it's own server.

56. Front­End
Performance

57. Front­End Performance: Points
● Tactics
● Minification (JavaScript / CSS)
– PHP 5.3 library: Assetic
● CSS Sprites
– Several online and offline tools
● GZIP
– Configured in the web server
● Cookies slow down the client
● Parallel downloads (use subdomains)
● HTTP Expires
– Configured in the web server

58. Front­End Performance: Tools
● Tools for Identifying Areas
● Yslow
● Firebug
● Google Page Speed
● Google Webmaster Tools
● Pingdom

59. Questions?
Mike Willbanks
Blog : http://blog.digitalstruct.com
Twitter : mwillbanks
IRC : lubs on freenode
Joind.in : http://joind.in/2838