Newest major version upgrade target for PostgreSQL 12.16

Based on the most recent information available, the newest major version upgrade target for PostgreSQL 12.16 is version 17. Amazon RDS for PostgreSQL now supports major version 17, starting with PostgreSQL version 17.1.

However, it's important to note that while direct upgrades to higher versions may be possible, it's generally recommended to upgrade one major version at a time. This step-by-step approach allows you to test and ensure compatibility at each stage, reducing the risk of unexpected issues.

For PostgreSQL 12.16 specifically, you have several upgrade options:

1. You can upgrade to version 13, then to 14, 15, 16, and finally to 17 if desired.
2. You might be able to skip some versions and upgrade directly to a higher version, but this should be done with caution and thorough testing.

Before proceeding with any upgrade, it's crucial to:

1. Test the upgrade process in a non-production environment
2. Ensure your applications are compatible with the target version
3. Back up your databases
4. Plan for potential downtime, especially for major version upgrades

Remember that when you upgrade the primary instance, any associated read replicas will also be upgraded to the same version. Additionally, most PostgreSQL extensions are not automatically upgraded during the engine upgrade process and will need to be upgraded separately after the engine upgrade is complete.

To determine the exact upgrade paths available for your specific instance, you can use the AWS CLI to query the available upgrade targets for your current version. This will give you the most up-to-date and accurate information for your specific setup.
Sources
Amazon RDS for PostgreSQL now supports major version 17 - AWS
RDS Postgres upgrade | AWS re:Post
Choosing a major version for an RDS for PostgreSQL upgrade - Amazon Relational Database Service

The first URL is with regards to RDS, while the second is with regards to Aurora. You should see if you use RDS or Aurora. If you wish to move to a version that is not supported with direct upgrade, you can have two steps, move to latest version supported by direct upgrade and than upgrade to a more recent version. In any case make sure to test the upgrade process, in your test environment. You can recover from a snapshot an create a test database and than test the upgrade process.