Transparent upgrade of replicaset Atlas MongoDB 5 -> 6 seems not to be supported

[Michael S]

Hello

we are using reactivemongo driver 1.1.0-RC12 to be able to upgrade to MongoDB 6 (thanks!).

We detected a bug, which we could reproduce every time (with several apps): https://github.com/ReactiveMongo/ReactiveMongo/issues/1312

• When being connected to a MongoDB 5 replicaset, a transparent upgrade of the replicaset seems not to be supported by the driver.
• Driver is in fact generally capable of connecting to MongoDB 6 - there was a incompatible change see  https://dochub.mongodb.org/core/legacy-opcode-removal..
• ..but in this scenario it still connects to MongoDB 6 nodes using those opcodes.
• A restart of the app (driver) seems to be necessary.

Take care if you plan to upgrade applications without downtime.

Any comments welcome, did anybody also experience this issue?

BR

Michael

[Cédric Chantepie]

I cannot reproduce such issue.

Temporary errors can happen (even if I personnally do not remember so).

We have upgrade from 5 to 6, and then to 7 without downtime.