Autoscaling happens when there’s sustained (for a few minutes), significant, traffic to a region. This is based on your app’s soft limit.
Autoscaling is probably not being triggered by a monitoring system, but should be by real-world traffic.
The way regions currently work, we don’t guarantee app instances will be placed in all the specified locations. It’s a list of regions where Fly may put instances.
Right now, we don’t support a “minimum per region” setting. The only way to achieve this is via Anchor scaling (incompatible with autoscaling) or if you use --max-per-region with your fly scale count (fixed count, will not autoscale).
If this is only for benchmarking purposes: the best way would be to set a fixed count with a --max-per-region so you can get your instances exactly where you want them.
If this is for real-world traffic: you can tweak your soft limit so autoscaling is triggered more often.