add ec2 instance with pgbouncer

[hrodmn]

Overview

titiler-pgstac and any other serverless functions that can send many simultaneous requests to the pgstac database can quickly overwhelm the database resources. This PR adds an EC2 instance running pgbouncer to the MAAP eoAPI stack, providing connection pooling for titiler-pgstac requests.

Features

• Connection pooling sets the maximum connections to the actual database instance to 25
• pool_mode = transaction provides high performance for many inbound requests
• CloudWatch logging is set up for the pgbouncer process
• With these changes, the test deployment which is running a t3.micro RDS instance is performing significantly better* than the t3.small instance on the dev deployment
  • based on subjective assessment of slippy map tile rendering.
  • Without these changes the test deployment is basically unusable for rendering large-scale mosaics.

Questions

• Are there any other security measures we need to consider with this approach? @jjfrench
• Should the pgbouncer configuration settings be dynamic according to the pgstac database size? @bitner

This is one approach for solving https://github.com/NASA-IMPACT/active-maap-sprint/issues/1052

[jjfrench]

Sorry for the late review! I left some comments/questions but everything looks good overall! 🚀