Rollback strategy from 3.0.4 to 2.4.10

[Karthik Bhat]

I have Mongo version 2.4.10 in Production.
If I do a rolling upgrade from 2.4.10 to 2.6.x to 3.0.x, how can I roll back in case things went messy?

As per mongodb documentation, "Once upgraded to MongoDB 3.0, you cannot downgrade to a version lower than 2.6.5.".
Is it telling me that I cannot downgrade to a version lower than 2.6.5 from 3.0 in one step? OR that I cannot downgrade with 3.0.x -> 2.6.5 (or above) -> 2.4.10 at all?

If I cannot downgrade to a version lower than 2.6.5, then should I take the backup of entire cluster for reverting back to 2.4.10?

[Stephen Steneker]

Hi Karthik,

I would definitely recommend testing your upgrade process (and deployment after upgrading) in a staging/QA environment first, and taking a backup before any production upgrades. In particular, it's worth looking for any compatibility changes or performance regressions for your workload.

Compatibility changes should be covered in the release notes for the server and the driver(s) you are using:

 - http://docs.mongodb.org/master/release-notes/2.6-compatibility/

 - http://docs.mongodb.org/master/release-notes/3.0-compatibility/

There are certainly steps after which downgrading will become more difficult (eg. after upgrading config metadata, index formats, authorization models). Reverting to a previous backup is probably the extreme case (versus fixing issues with an upgrade process that has been successfully tested in staging/QA).

If you want to be cautious on the upgrade you should upgrade from 2.4 to 2.6 first and allow your deployment to settle for a period of time before continuing with the upgrade to 3.0. 

Downgrade caveats are also noted in the manual:

 - http://docs.mongodb.org/manual/release-notes/2.6-downgrade/

 - http://docs.mongodb.org/manual/release-notes/3.0-downgrade/

Regards,

Stephen