JetStream - Updating consumer from R3 to R1 doesn't work

[goku321]

nats-server: v2.8.4
nats.go: v1.16.0
NATS cli: v0.0.33

Step to reproduce:

1. Setup a 3-nodes JetStream cluster.
2. Create a stream with a replica count 3.
3. Create a consumer using nats.go client with a replica count 3.
4. Publish and consume some messages.
5. Update the consumer's replica count to 1 using nats.go client

Expected results

1. Replica count for the consumer should get updated to 1.
2. Consumer should have no replicas or metadata on replica nodes.
3. nats con info should not show any replicas field for a R1 consumer

4. When the leader node is killed while consuming, the client should get a "Consumer Migration" message (since, it is R1 now).

Actual results

1. nats con info does show replica count as 1 (which is correct)
2. Consumer still have its metadata on other nodes and it's being updated regularly (confirmed with ls -l)
3. nats con info shows replicas field

4. When the leader node is killed, the client gets a "Leadership Change" message (that means, it is still > R1)

[matthiashanel]

@goku321 I can confirm that this is not implemented

[goku321]

Thanks @matthiashanel for confirming. As a workaround, we are creating a new R1 consumer with start sequence and copying its config from the existing R3. Here's the example code. To make sure that this R1 resumes from where the old R3 left, we are setting the start sequence of R1 to consumerInfo.Delivered.Stream+1 (of R3). I tested this for a few cases and it seems to be working fine. Would there be any case that this might fail?