Making multiple Amazon EC2 instances write to a single database

Question

I have a website that get a lot of traffic on weekends. What visitors do on this site is - They answer quiz questions and submit as soon as possible.

My server gets a lot of traffic when the javascript tries to fetch question from the server and when they are trying to submit into the database.

The application is created using mysql and PHP. When my visitors submit, I want them to be able to submit to a single database and not multiple databases since an EBS volume can only be attached to one EC2 instance.

The traffic is much so I need more instance to support any running instances during traffic spike. What can I do to achieve such a high availability that provides me with single repository for all answers submitted by my visitors? Thank you.

Answer 1

You can use Amazon RDS. Basically, it's a DB outside an instance without a hard disk. You can set multiple instances to connect to your RDS.

You can also add ec2 instances for horizontal scaling so as to address your traffic spike problems.

Answer 2

You have different options to be able to scale your application:

1. If everything is running on a single instance right now, you can separate them to two instances: one for the web server and one for the database. With EC2, you can use security groups to allow access from the web server to the database.
2. If the web server becomes the bottleneck, add more instances and use Amazon's ELB to load balance across the various instances. You can even use autoscaling to dynamically increase and decrease the number of running instances based on traffic.
3. If the database is the bottleneck, you can first start by moving it to a larger instance type. You can also use Amazon's RDS service for a managed mysql service.
4. To further add capacity, you can use read replicas (if the app is read-intensive) to distribute the load.

Up to point 4 above, you should be able to do it all without modifying your application. To further scale up, there are a couple more things to look at:

• Add caching: use memcached or Amazon's Elasticache. This could add a big boost.
• Move to something like Amazon's DynamoDB, where you can easily add read and write capacity as needed.

Good luck!