Tuesday, January 3, 2012

Architecting an Highly Available and Scalable WordPress Site in AWS

Why this presentation ?
  • WordPress is used by over 14.7% of Alexa Internet's "top 1 million" websites
  • As of August 2011 WordPress powers 22% of all new websites
  • As of December 2011, version 3.0 had been downloaded over 65 million times
  • Provide some architectural insights to build Highly Scalable and Available WordPress sites in AWS
  • Help startups and companies who are new to AWS- WordPress with some blueprints


FAQ for this architecture can be found here

WordPress Architecture Requirements in AWS
  • Ability to Serve millions of Pages per day
  • Ability to scale out/down dynamically depending upon traffic
  • Ability to perform well even with scaling demands 
  • Should be Highly available without Single Points of Failure
  • Automated Operations – Backup and Monitoring
  • Cost effective 
Why AWS is better for WordPress Scaling?
  • AWS provides flexibility to Scale up and Scale out
  • AWS provides Building block services which is inherently robust and fault tolerant
  • AWS provides full range of options from CDN , OS flavors , Storage Pool , Database , Load Balancers , Monitoring etc
  • Pay as you go – Save cost by leveraging Auto Scaled WordPress EC2 instances
  • We can start small and grow big in AWS

AWS building blocks used
  • Amazon Route53 for managing and answering DNS queries
  • Amazon Elastic Load Balancer for load balancing HTTP/S requests to WordPress Instances
  • RDS MySQL Database Server for storing the WordPress content
  • Simple Storage Service (S3) for storing the WordPress application assets , snapshots and log files
  • Amazon CloudFront CDN for delivering the application static assets from nearest edge locations
  • Amazon CloudWatch for monitoring and sending SNS alerts
Highly Scalable Architecture for WordPress application



Load Balancing Tier
  • Amazon Elastic Load Balancing will Load balance the http requests to WordPress EC2 instances
  • ELB will direct the requests to WordPress EC2 across Multiple Availability Zones ( for HA)
  • Health check , LB algorithms and SSL termination will be done by the Load Balancer
  • Amazon Elastic Load Balancing can keep expanding its capacity automatically depending upon the traffic 
  • Amazon ELB works with Route 53 and Auto Scaling seamlessly
  • Amazon ELB is priced @“ Pay for use” model
  • Amazon ELB is a managed service , so No Maintenance headaches , SW/HW upgrades ,Capacity planning  and manual intervention for expansion
How scalable is this architecture ?
  • Scalability and Elasticity is built in most of the layers in this architecture
  • WordPress EC2 instances can be scaled out and down depending upon the traffic 
  • We can expand the number of WordPress EC2 instances from 1 to 100+ automatically during load peaks
  • We can reduce the number of WordPress EC2 instances from 100+ to 1 automatically during valleys
  • Can serve millions of pages with ease 
  • Pay only for the EC2 instance hours used
  • Read Scalability is built in the Database layer with RDS Read Replicas
  • New RDS Read Replicas can be added / removed with ease
  • Tips:  During Campaigns alone we can run more RDS Read Replicas , Not more than max 5 RDS Read replicas are recommended , Keep Read Replica’s and RDS Master same EC2 size for better performance.
  • Clustered + Distributed File System of the Storage pool layer can be manually scaled in case needed
  • Minimum 2 EC2 Large instances should be used for Storage Pool Layer ( for HA and better IO)
  • Design the Storage Pool Layer with HA (very critical)
  • AWS building blocks like S3 , CloudFront , CloudWatch , SNS used in this architecture  are inherently designed for scalability

How High Availability and Fault tolerance is built in this Architecture ?
  • HA @ WordPress Layer
  • Multiple WordPress EC2 instances avoid single point of failure
  • WordPress EC2 instances are launched across multiple –AZ’s inside a region for High Availability
  • HA @ DB Layer
  • RDS MySQL Master and Standby are launched in 2 different availability zones for High Availability
  • RDS Read Replicas are created in Multiple –AZ’s
  • HA @ Storage Pool Layer
  • GlusterFS is used for the Storage Pool Layer
  • Two EC2 instances used for Storage Pool Layer
  • Storage Pool is setup in replicated mode for High Availability 
  • AWS building blocks like S3 , Cloud Front , CloudWatch , ELB , SNS ,EBS used in this architecture are inherently designed for Fault tolerance and HA
How the Database Tier is Architected ?
  • RDS Master and Standby provide High availability
  • RDS Read Replicas provide Read performance
  • HyperDB plugin is configured to use multiple endpoints like RDS master and RDS read replicas in this architecture
  • DB security groups will allow DB access only to WordPress EC2 instances
  • Periodic Dumps , Snapshots and Point in time recovery is possible in this architecture
What performance aspects are taken care in this Architecture ?
  • APC (or) Xcache plugin can be used for PHP opscode caching
  • W3TotalCache+CloudFront (or) BatCache+Memcached can be used for Page caching
  • Multiple RDS Read Replicas for Read performance
  • RDS Master and Read Replicas are separated to get independent write and read performance
  • Amazon ELB + Auto Scaling improves the overall Site performance when the load increases
Content Delivery Network
  • Amazon CloudFront will be the Content Delivery Network (CDN) 
  • W3TotalCache plugin will be configured to use Amazon CloudFront for enhanced performance and reduced latency
  • Static assets , templates , themes , images etc will delivered from the nearest edge locations of the CDN
Deployment
  • Distributed File Storage Pool is configured between WordPress Management and Content instances
  • WordPress Management and Content instances share the common storage pool for files and plugins
  • Deployment of files and plugins will happen through the WordPress management node
  • Files and plugins will be immediately available for use in the auto scaled WordPress EC2 instances
Monitoring and Alerts
  • Amazon CloudWatch will monitor the CPU and Network utilization of the entire setup
  • Amazon CloudWatch alarms configured with Amazon SNS provides Email/SMS alerts to System Administrators
Backups
  • Custom ops scripts will backup the necessary files from Storage pool to S3 periodically
  • S3 can be configured to remove old backups automatically
  • RDS MySQL is configured to take periodic data dumps and DB snapshots
  • RDS layer can be recovered point in time from the backups

Security
  • Suitably hardened OS for WordPress Mgmt and WordPress instances
  • Firewall (or) AWS security groups configured between all the layers in the architecture
  • SFTP/FTP access only to the WordPress management node
  • AWS IAM policies to manage user account access
  • Install WordPress Security plugins 

Advantages
  • Highly Available and Scalable architecture
  • Can elastically scale out to serve millions of hits in a day
  • Can grow with load demands in future
  • Usage of inherently fault tolerant AWS building blocks adds Stability
  • High performance using CDN and suitable cache plugins
  • Monitoring , Backup and Recovery is built in
  • Pay for use 

Disadvantages
  • Complex to setup and maintain
  • Will not be ideal for smaller sites that do not need scale
  • Will not be cost efficient for sites that have less traffic
Key Points to Remember 
  • Log files generated in WordPress EC2 instances have to rotated 
  • Use Amazon EBS for Storage Pool and WordPress EC2 instances 
  • Start with EC2 m1.Large Instances for the storage pool and WordPress instances
  • More Memory – Better Performance for DB
  • Start with RDS Large for Master 
  • Keep RDS Master and RDS Read Replica’s in same size to improve read performance
  • RDS MySQL supports only Innodb engine
  • Separate the WordPress Management and WordPress Content instances for scalability
  • Do not Scale out/down rapidly in a hour, it will cost more in AWS
  • Combine AWS On-Demand and Reserved Instance pricing to get more savings per month
  • Amazon Availability Zones(AZ’s) are distinct physical locations with Independent power , cooling ,network and security having Low latency network connectivity between them inside the same region
  • Leverage them in WordPress , Storage Pool and DB layers for HA as mentioned in the architecture 

2 comments:

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