The disadvantage for successfull business growth is the increased infrastructure cost to support this. This becomes more significantly complex when using managed services, because the availability of upsizing becomes effectively doubling of the compute cost. When it comes to RDS database instances; for example the AWS RDS r6g family that uses 2x,4x,8x,12x,16x,24x; you lose granularity if your application cannot scale-out, it must scale-up. The AWS RDS r8g family goes from 24x to 48x, there are no incremental steps. Some instance types (e.g. r6i, m6i) will give you 24x and 32x.
If you are a small organization and you run a High Availability (HA) database infrastructure on RDS using r6g.4xlarge, that starts at $2,556 per month with on-demand pricing, but drops to $1,476 per month with a 1 year reserved instance (RI) reservation. NOTE: Pricing varies per region.
You should of course purchased (Size-flexible reserved DB instances](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_WorkingWithReservedDBInstances.html#USER_WorkingWithReservedDBInstances.SizeFlexible ) to be able to cater for incremental growth during the year.
If you have to upsize, your monthly on-demand cost will double. You have to make a decision whether to cover this with RI reservations or not?
Your successful growth of your monolith database application leaves you stuck with.
The performance benefits of moving from r6g to r8g may be ideal, however you are locked into a RI contract.
OCI counters this with Flexible Shapes
