As the requirements from your web service grow, it may be tempting to abandon old code and rewrite it using new technologies that promise to solve all your problems.
While sometimes this is a good idea, more often than not such a move ends up being disastrous - the new code suffers from new problems, while all the bug fixes that made the old code rock solid are lost in the process.
Depending on your specific requirements, it may be possible to deploy new technologies in a manner that preserves your existing investment in your proven, debugged core code. I'd love to share our experience on integrating a host of scalability related technologies - CDN, memcache, Varnish, and others into our architecture while maintaining our original code base intact.
Eran Sandler gave this talk in ILTechTalks week his presentation attached