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ScalableArchitectures 101
MNPHPFeb 3, 2011
Mike Willbanks Blog: http://blog.digitalstruct.comTwitter: mwillbanks IRC: lubs on freenode
Scalability?
Your application is growing, your systems are slowing and growth is inevitable...
● Where do we go from here?● Load Balancing● Web Servers● Database Servers● Cache Servers
● Job Servers● DNS Servers● CDN Servers● FrontEnd Performance
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
The Next Step...
Single Separation Syndrome
● Separation of Web and Database
● Fix the main disk I/O bottleneck.● However, we can't handle our current I/O, CPU or
amount of requests on our web server.
Load Balancing
Load Balancing Our Environment
Several Options
● DNS Rotation (Little to No Cost)● Not very reliable, but works on a small scale.
● Software Based (Commodity Server Cost)● HAProxy, Pound, Varnish, Squid, Wackamole,
Perlbal, Web Server Proxy...
● Hardware Based (High Cost Appliance)● Several vendors ranging based on need.
– A10, F5, etc.
Routing Types of Load Balancers
● Round Robin● Static● Least Connections● Source● IP● Basic Authentication
● URI● URI Parameter● Header● Cookie● Regular Expression
Open Source Software Options
● 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
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
Sample HAProxy Configuration
global log 127.0.0.1 local0 log 127.0.0.1 local1 notice maxconn 4096 user haproxy group haproxy daemon
defaults log global mode http option httplog option dontlognull retries 3 option redispatch maxconn 2000 contimeout 5000 clitimeout 50000 srvtimeout 50000
listen localhost 0.0.0.0:80 option httpchk GET / balance roundrobin cookie SERVERID server serv1 0.0.0.0:8080 check inter 2000 rise 2 fall 5 server serv2 0.0.0.0:8080 check inter 2000 rise 2 fall 5 option httpclose stats enable stats uri /lb?stats stats realm haproxy stats auth test:test
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...
Sample Pound Configuration
User "www-data"Group "www-data"LogLevel 1 Alive 30Control "/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
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
Sample Varnish Configuration
backend default1 { .host = "127.0.0.1"; .port = "8080"; .probe = { .url = "/"; .interval = 5s; .timeout = 1s; .window = 5; .threshold = 3; } }
backend default2 { .host = "127.0.0.1"; .port = "8080"; .probe = { .url = "/"; .interval = 5s; .timeout = 1s; .window = 5; .threshold = 3; } }
director default round-robin { { .backend = default1; } { .backend = default2; } }
sub vcl_recv { if (req.http.host ~ "^127.0.0.1$") { set req.backend = default; } }
What We Need to Remember
● 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
Web Servers
Several Options
● Apache● IIS● Nginx● Lighttpd● etc.
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 will likely be in Xforwardedfor.● SSL will not be in $_SERVER['HTTPS'] and
HTTP_ header instead.
What We Need to Remember
● 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?
Other Thoughts
● Running PHP on your web server may be a resource hog, you may want to offload static content requests to 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.
DatabaseServers
Where We All Start
Single Database Server
● Lots of options and steps as we move forward.
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.
Multiple Slaves
Single Master, Multiple Slaves
● It is a great time to start to implement connection pooling.
Multiple Masters
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.
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
What We Need to Remember
● 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.
CacheServers
(not full page)
Caching
“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.
Caching
In The Beginning
● Single Caching Server
● Start to cache fetches, invalidate cache on write and write new cache, always reading from the cache.
Distributed Caching
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.
The Read / Write Process
In the most simple form...
What We Need to Remember
● 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?
JobServers
“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
Messages are Everywhere
What are Message Queues
● 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.
Where We All Start
Single Job Server
● Lots of options and steps as we move forward.
Producer Message QueueServer
ConsumerQueue Receive
Distributed Job Servers
Distributed Mania
● Load balance a message queue for scale
● Can continue to create more workers
Producer
Message QueueServer
Consumer Consumer Consumer ConsumerConsumer
Message QueueServer
Message QueueServer
Producer Producer
Why are Message Queues Useful?
● Asynchronous Processing● Communication between Applications / Systems● Image Resizing● Video Processing● Sending out Emails● AutoScaling Virtual Instances● Log Analysis● The list goes on...
What We Need to Remember
● 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 :)
DNS Servers
What to do
● Just about every domain registrar runs DNS● 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!● A “cheaper” provider is DNS Made Easy.
– Yes the interface is ugly.
What to look for...
● Wildcard support● Failover / Distributed● CNAME support● TXT support● Name Server support
CDN Servers
Why Use a CDN
● Free your bandwidth● Free your server from serving basic files● Distributed servers around the globe
What you need to know
● 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.
What's the best?
● 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.
FrontEndPerformance
Discussion Points
● Tactics● Minification (JavaScript / CSS)● CSS Sprites● GZIP● Cookies are evil● Parallel downloads (using subdomains for serving● HTTP Expires
Discussion Points
● Tools● Yslow● Firebug● Google Page Speed● Google Webmaster Tools
Questions?
Mike Willbanks Blog: http://blog.digitalstruct.comTwitter: mwillbanks IRC: lubs on freenode
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