How to Scale with Ruby on Rails

By George Palmer of Covers:
* How you start out: shared hosting,  web server DB on same machine. Move two 2 machines. Minimal code changes.
* Scaling the database. Add read slaves on their own machines. Then master-master setup. Still minimal code changes.
* Scaling the web server. Load balance against multiple application servers. Application servers scale but the database doesn't.
* User clusters. Partition and allocate users to their own dedicated cluster. Requires substantial code changes.
* Caching. A large percentage of hits are read only. Use reverse proxy, memcached, and language specific cache.
* Elastic architectures. Based on Amazon EC2. Start and stop instances on demand. For global applications keep a cache on each continent, assign users to clusters by location, maintain app servers on each continent, use transaction replication software if you must replicate your site globally.