Scalable Web Architecture

Scalable web architectureLAMP (& AWS infrastructure)

Aleksandr Tsertkov

LAMP

LAMP: Platform

L - Linux / Unix

A - Apache / lighthttpd / nginx

M- MySQL / PostgreSQL / SQLite

P - PHP / Python / Perl / Ruby

LAMP: Why LAMP

– We know it!– Proved by very big guys (Facebook,

YouTube, LiveJournal, etc)– Plenty of shared experience on the web– Its flexible and extendable– Easy to find engineers– Easy to maintain– Its cheap

LAMP: Who use it

Let’s take top 10 Internet sites according to Alexa.

• Google

• Yahoo!

• YouTube

• Facebook

• Windows Live

• MSN

• Wikipedia

• Blogger

• Baidu

• Yahoo! Yapan

Who use LAMP? 5 of 10

System design (SD)

SD: Key points

• Scalability

• HA (High Availibility)– Backup & restore strategy!!!

• Fault-tolerant

• SA (Share Nothing)

SD: Load scalability

“ Load scalability: The ability for a distributed system to easily expand and contract its resource pool to accommodate heavier or lighter loads. ”

-Wikipedia

SD: Horizontal scalability

Adding new nodes to a system for handling growing load and removing nodes when load decreases.

SD: High Availibility

Complex: High availability is a system design protocol and associated implementation that ensures a certain absolute degree of operational continuity during a given measurement period.

Simple: maximum uptime, minimum downtime.

SD: Fault Tolerant

System should be able to continue function normally even if some of its components fail.

No single point of failure.

SD: Share Nothing

“ A shared nothing architecture (SN) is a distributed computing architecture in which each node is independent and self-sufficient, and there is no single point of contention across the system. “

- Wikipedia

SD: Share Nothing

Can be achieved on different application layers separately:

• Database: data partitioning / sharding

• Cache: memcache client side partitioning

• Computing: job queues

SD: Typical web architecture

• Load balancer

• Several web servers

• Database server(s)

• Shared file server (NAS) (if really needed)

SD: Typical web architecture

Database server

Web server-1

Web server-2

Web server-n

Load balancer (LB)

File server

SD: Typical web architecture

• Each of these components / layers can be scaled separately.

• Database is usually the toughest part to scale.

SD: Scaling database

Master-Slave Replication variants:

1. Read/Write queries to Master, Read only from Slaves

2. Writes to Master, Reads only from Slaves

SD: Scaling database

Master should be very powerful machine, but sooner or later you will hit the IO limit.

Data partitioning / sharding is used to distribute data across number of Masters spreading load between them (horizontal scaling).

SD: Scaling database

Common data(master)

Slave-1

Slave-n

Partition-1(master)

Slave-1

Slave-n

Partition-n(master)

Slave-1

Slave-n

User-AUser-BUser-C

User-DUser-EUser-F

SD: Caching strategy

Hierarchy of caches should be used for optimal performance and efficiency.

Local memory -> memcached -> local disk

SD: Caching hierarchy

• App server local in memory cache for highly common items (speedup scripts bootstrapping)

• Distributed cache system (memcached) for caching database queries and general purpose cache

• App server file cache for big size items

SD: High-CPU app servers

For High-CPU computing operations like audio/video processing dedicated application servers should be used.

Good control over them can be achieved using job queue.

Video: check YouTube Platform ;-)

SD: Web servers optimization

• General web servers (apache)

• COMET web servers

• Static content web servers

• Content Delivery Network (CDN) should be used for static public content.

SD: Static files strategy

• Network attached storage (NAS)– Distributed network file system (Lustre,

GlusterFS, MogileFS)– Not distributed (NFS)

• Fault-tolerance and data redundancy are required!

SD: Static files strategy

• Distributed filesystem is complex but in a perfect world it should give us what we need: performance, redundancy, fault-tolerance.

• Static content web servers can run on DF nodes!

SD: Load balancers

• Software or hardware load balancers

• Traffic distributed between several load balancers using round robin DNS

• HA solution for load balancers

SD: Complete picture

Amazon Web Services

AWS: What is AWS?

• Amazon is not only about books • Amazon Web Services provide

infrastructure web services platform in the cloud.

AWS: Why AWS?

• Because it has everything what we need:– EC2: Elastic Compute Cloud

• EBS: Elastic Block Store• CloudWatch: monitoring service with auto scaling• Elastic Load Balancing

– S3: Simple Storage Service– Cloud front (CDN)– SQS: Simple Queue Service

AWS: EC2

• Easy to deploy (os images)• Easy to scale up and down on demand

(deals with peaks) with Auto Scaling• Out of the box monitoring with

CloudWatch• Out of the box load balancing with Elastic

Load Balancinghttp://aws.amazon.com/loadbalancing

AWS: S3 & CloudFront

• Out of the box CDN with CloudFront

• DFS (sort of) with S3

• Very reliable

AWS: Services on top of AWS

Some like AWS so much that they have created own cloud services on top of it

• RightScale www.rightscale.com

• GoGrid www.gogrid.com

AWS: Panacea?

• AWS is indeed good to start with since its fast and cheap.

• In a long time term if everything goes as expected and profit increases it might be better to build own cloud infrastructure and migrate to it at some point.

Thank you!