From the logs, the downscale operation for the RDS Aurora cluster involved several restarts and failovers but no downtime for reading or writing operations.

1. At 16:42–16:47: Both the reader and writer instances were restarted as part of the instance class modification (from R5 to T3). This likely involved some downtime for the instances during the restarts but not for database operations themselves.

2. At 16:49: A failover occurred, promoting the former reader to writer and transitioning the former writer to reader. The T3 instance became the new writer, and the R5 writer was demoted to reader.

3. At 16:54: The final configuration changes were applied, and the instances were fully transitioned to their new roles (R5 to T3 for writer and reader).

Conclusion:

There was no downtime during the entire process. The failover was smooth, and both reading and writing operations continued uninterrupted.