Many things. Here's a list off the top of my head:
MySQL RDS acts like it's just regular MySQL minus SUPER privilege. So it will not accept various important inputs. For example, GTID state will be rejected. Even just pre-GTID log sequence numbers are barely supported. Various SQL SECURITY things are rejected. The suggestions for importing data using any of these features vary from scary nonsense (just ignore GTID numbers!) to absurd hacks (run sed on your mysqldump output to remove SQL SECURITY!).
The docs basically don't acknowledge that GTID matters in a RDS-to-or-from-non-RDS setup. The suggestions don't seem like they deserve to work. (Azure at least has some documentation for GTID, but it involves using fancy barely-documented APIs just to import your data.)
Replication will just break if you accidentally use a feature that RDS can't handle.
For something that could easily cost hundreds to thousands of dollars per month, I expected to be able to run an unmodified mysqldump and have RDS accept the output, process it correctly, and take my money. Nope, didn't happen.
MySQL RDS acts like it's just regular MySQL minus SUPER privilege. So it will not accept various important inputs. For example, GTID state will be rejected. Even just pre-GTID log sequence numbers are barely supported. Various SQL SECURITY things are rejected. The suggestions for importing data using any of these features vary from scary nonsense (just ignore GTID numbers!) to absurd hacks (run sed on your mysqldump output to remove SQL SECURITY!).
The docs basically don't acknowledge that GTID matters in a RDS-to-or-from-non-RDS setup. The suggestions don't seem like they deserve to work. (Azure at least has some documentation for GTID, but it involves using fancy barely-documented APIs just to import your data.)
Replication will just break if you accidentally use a feature that RDS can't handle.
For something that could easily cost hundreds to thousands of dollars per month, I expected to be able to run an unmodified mysqldump and have RDS accept the output, process it correctly, and take my money. Nope, didn't happen.