MONGO_UPDATE.md

How to update MongoDB

1. Enable migration

chmod +x migrations/pre_refresh/feature_compatibility/00-adopt_version.sh

This migration or pre-refresh script will make sure the feature compatibility version of the existing mongodb instance is set correctly for the update to pass through successfully.

{ is_mongod_running || start_mongod; } &&
  is_mongod_ready &&
    v=$(mongod_version_excluding_patch) &&
      is_mongod_primary &&
        { is_feature_compatibility $v || set_feature_compatibility $v; } &&
          stop_mongod

2. Add new MongoDB link

TODO: simply this, use a plugin

Go to https://www.mongodb.com/try/download/community and get the archive link of the desired mongodb version. Open snapcraft.yaml and add that to the mongodb part source.

NOTE: use the mongodb-tools part when mongodb >=5.0.0

3. Increase epoch

Assuming the current epoch is n, change the epoch to n*.

From after this, if performing consecutive mongodb updates in a short amount of time (no 100% chance of every install being auto-refreshed to latest revision), increase epoch by 1. See the table below.

MongoDB	epoch
1	n
2	n*
3	(n+1)*
4	(n+2)*
5 (final)	(n+3)

MongoDB	epoch
1	n
2	n*
3 (final)	(n+1)

4. Disable migration

Once snap released wwith desired mongodb version, disable the migration (keeping it won't necessarily do any harm, but why)

chmod -x migrations/pre_refresh/feature_compatibility/00-adopt-version.sh