We had the same experience with one of our main Rails apps recently. The original version was written in 2007 in Rails 1.2.x and Ruby 1.8.6. Since then, lots of

We had the same experience with one of our main Rails apps recently. The original version was written in 2007 in Rails 1.2.x and Ruby 1.8.6. Since then, lots of features have been added, which of course inflated LOC and increased gems/plugins dependency even further. We migrated the app to Rails 3.1 last year with the help of a number of gems that provide backward compatibility. Even though, it took much longer than what we planned. Majority of the files, be it models, controllers or views, had been touched and changed. The worse part was that we didn't have sufficient test suites to assist so lots of manual tests. Along the way, we gradually replaced those obsolete plugins/gems one by one, which was a pain but seemed to be worth it. Early this year we migrated the app to 1.9.3/3.2.x. Basically the same process but less painful, as most of the gems/plugins issues have been ironed out last year.