Spent a few hours dealing with errors on RDS when upgrading from a postgresql 10.6 to 11.1. In case someone else is dealing with the same problems, this might be helpful.
A few things to know about this database:
- PostGIS extension was installed but was not being used
- ip4r extension was installed but was also not used
This probably turned out to be a Good Thing (tm). If you are using PostGIS extensively, I wish you good luck.