Uploaded image for project: 'Documentation'
  1. Documentation
  2. DOCS-11987

Docs for SERVER-35731: Prevent a repaired node from re-joining a replica set


      Original Description


      When a mongod is started with --repair and data or metadata is modified by the operation, the instance will be unable to rejoin its original replica set without a full resync. The only way to add the instance back to a replica set would be to delete the local.system.replset collection or wipe the data directory entirely.

      Additionally, if a repair operation fails to complete for any reason, the instance will not be able to start again without the --repair option.

      Engineering Ticket Description:

      When MongoDB is started with --repair, the repair process will attempt to salvage data at the expense of potential data loss so that MongoDB can be started normally.

      If a user is unaware they have lost data, they may attempt to add the node back to its original replica set. In the worst-case scenario, this node will become primary and data will appear to go missing.

      There are currently no measures in place to prevent a secondary with data modified offline from re-joining its original replica set (even without repair).

      Solution: If repair modifies collections (not indexes), repair will add a top-level field "repaired: true" to the local.system.replset configuration document. This will invalidate the document and prevent the node from re-joining as a member of the replica set. When the server starts up again normally, a warning will be printed with instructions for performing a re-sync.



      Scope of changes (files that need work and how much)

      Impact to other docs outside of this product

      MVP (work and date?)

      Resources (e.g. Scope Docs, Invision)

            isabella.siu@mongodb.com Isabella Siu (Inactive)
            kay.kim@mongodb.com Kay Kim (Inactive)
            0 Vote for this issue
            3 Start watching this issue

              5 years, 20 weeks, 4 days ago