Handling migrations with MongoDb

There are basically two approaches:

1. Make sure that your application code can handle both "versions" of the data structure, and when saving, updates to the new structure
2. Write a migration script

I would probably go for option 1 as it's the method that allows you to gradually update, where as with option 2 you basically need to take down your application so that you can update the code (fast) and data (possibly slower) in one go.

Then later, or if you find it necessary do option 2 as well to migrate your data over. This then doesn't have to take down your site, and can happily run asynchronously in the background.

Strategies can be different. And they are depend on particular application.For sure for the sites like Facebook you will go with option #1 proposed by Derick to not hit your users at all, but if you have site that 'sells pizza' you for sure don't want make an effort to support both versions (current and new one), write more complex code, etc..

For such kind of apps simple patching may be better option:

1. Build server send application to 'Read mode', so anyone can read, but can't insert anything into database.
2. While prod in read mode i am taking database and apply patch.
3. Once patching done it make backup of database, stop web server, deploy new database and new application.

Sending application to read mode allow to decrease downtime, but again for sites that's 'sells pizza' you don't need read mode.

It seems like currently I am wanting to go with the migration option rather than a phasing out approach, so with this in mind can anyone recommend any tools for helping in this area

For those who are still looking for the solution, take a look at MongoMigrations, this tool exposes MongoDatabase (from the mongo csharp driver) for manipulations over database so you can use all features from the driver.