Modify - Minor Version Upgrade and Actions - Patch for Aurora PostgreSQL and PostgreSQL RDS

Question

Hi,
We are planning on doing the minor version upgrade and just want to ask for some clarification as we're a bit confused on the documentation.
We presume a minor version upgrade is staying on the same version based on the first version, i.e 15.1 to 15.10 for example with the first number remaining the same.
The Action -> Patch, is that for the underlying OS that is hosting the Aurora PostgreSQL / PostgreSQL RDS database, is that correct? 
Is there no option to let Patch run as part of the Minor Upgrade?
Is ZDP really zero downtime, we thought it is stopping/starting databases in the process too, isn't it? 
We just want to make sure as we have data mining connectors that are dependent on the IP address of the host/endpoint.
Any feedback much appreciated. Thanks in advance.

P.S.: The Action -> Patch / Patch Now option is a bit 'dangerous' that is doesn't have a "Are you sure" prompt :-)

re:Post Agent · Answer

You're correct about minor version upgrades - they involve staying on the same major version (the first number remains the same), such as upgrading from PostgreSQL 15.1 to 15.10. Minor version upgrades include changes that are backward-compatible with existing applications and typically involve patches to the binary installation of the database.

Regarding the "Action -> Patch" option, this applies patches to the database engine itself, not the underlying operating system. Operating system updates are managed separately by Amazon RDS.

There isn't an option to run OS patching as part of a minor version upgrade because they are separate processes. Minor version upgrades can be initiated either manually by modifying your database or automatically by enabling the "Auto minor version upgrade" option.

As for Zero-Downtime Patching (ZDP), it's not truly "zero" downtime in all cases, but it significantly minimizes downtime. ZDP allows both minor version upgrades and patches to be applied with minimal impact to your Aurora PostgreSQL DB cluster. It preserves current client connections throughout the upgrade process, except for certain cases like long-running queries or transactions.

For RDS PostgreSQL, the downtime experience depends on your deployment:
- For Multi-AZ DB instance deployments, Amazon RDS simultaneously upgrades the primary and standby instances, which might cause unavailability for several minutes.
- For Multi-AZ DB cluster deployments, the downtime is typically reduced to approximately 35 seconds, and when used with RDS Proxy, it can be further reduced to one second or less.

If your data mining connectors depend on the IP address of the host/endpoint, you should be aware that while the endpoint remains the same after upgrades, there might be brief periods of unavailability during the process.

And yes, it's worth noting that the "Action -> Patch" option doesn't have a confirmation prompt, so caution is advised when using this option.  
**Sources**  
[Upgrades of the RDS for PostgreSQL DB engine - Amazon Relational Database Service](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_UpgradeDBInstance.PostgreSQL.html)  
[Performing a minor version upgrade - Amazon Aurora](https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/USER_UpgradeDBInstance.PostgreSQL.MinorUpgrade.html)  
[Mastering PostgreSQL Upgrades: Your Ultimate RDS/Aurora Handbook | AWS re:Post](https://repost.aws/articles/AR5EBX6dQMQjupYHkvuqP9TA/mastering-postgresql-upgrades-your-ultimate-rds-aurora-handbook)  
[Understanding PostgreSQL Version Upgrades in RDS/Aurora: A Comprehensive Guide | AWS re:Post](https://repost.aws/articles/AR5EBX6dQMQjupYHkvuqP9TA/understanding-postgresql-version-upgrades-in-rds-aurora-a-comprehensive-guide)

Modify -> Minor Version Upgrade and Actions -> Patch for Aurora PostgreSQL and PostgreSQL RDS

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