If your web application is static, it may be easier or cheaper to host it on Amazon Simple Storage Service (S3) instead of an EC2 instance. In S3, you can store sets of files in web-accessible folders, called buckets. S3 allows you to designate any bucket as a website. You define an index document (in other words, a start page) and a policy stating who can access the site. You can then interact with your pages from the bucket as if they were hosted on a traditional web server.
Not all web applications are appropriate for S3. If your app uses a server-side scripting language such as PHP, JSP, or ASP.NET, then you should host the app on your own EC2 instance. However, client-side scripting languages such as JavaScript are appropriate for S3. Applications built with the out-of-the-box Esri Web APIs and viewers should work on S3.
A benefit of hosting your page in S3 is the potential to use the Amazon CloudFront delivery service. This is an Amazon web service that hosts your content on various servers around the world, optimizing your file delivery speed among geographically dispersed users.
For full information about how to host a website on S3, see the Amazon Web Services documentation.