Minor version upgrade for Aurora Postgresql version 14.x

Question

Hello,
We are planning to upgrade our Aurora PostgreSQL cluster from version 14.x to 17.x using Blue/Green Deployments. The minimum required version for this approach is 14.9 or later. Since our current version is 14.15, an in-place minor version upgrade is required before proceeding.
We have also received a notification from AWS regarding a minor version upgrade and would appreciate your support on the following points:

1. Zero-Downtime Patching (ZDP)
	•	Is Zero-Downtime Patching (ZDP) equivalent to performing an in-place minor version upgrade using the following steps?
	◦	Select the database cluster and click Modify
	◦	Under DB engine version, choose the target version
	◦	Select Apply immediately

2. ZDP Procedure
	•	If ZDP is not equivalent to an in-place minor upgrade, could you please clarify the correct procedure?
	•	Should we follow the section “Upgrading the Aurora PostgreSQL engine to a new minor version” in the AWS documentation below? https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/USER_UpgradeDBInstance.PostgreSQL.MinorUpgrade.html#USER_UpgradeDBInstance.PostgreSQL.Minor.zdp

3. Reader Requirement for Minimal Downtime
	•	If the current database cluster has only a writer instance and no readers, is it recommended to add a temporary reader instance to minimize downtime during the upgrade for ZDP and In-place minor upgrade?

Florian Turnwald · Answer

**While the steps described in the answer of the re:Post Agent for a minor upgrade are correct, there are two important points to clarify:**
- **Version Requirement:** You mentioned being on version 14.15. Since the minimum requirement for Blue/Green Deployment to a higher major version is 14.9, you are actually already compliant. An additional minor upgrade is not technically required to start your Blue/Green Deployment to 17.x.
- **ZDP vs. Failover:** Zero-Downtime Patching (ZDP) is designed to patch the engine in place without a reboot or failover by "preserving" the connection. Adding a Reader instance is excellent for High Availability in general, but it doesn't technically "improve" ZDP. In fact, if a failover occurs, it is by definition not a ZDP event anymore.

Since you are already on 14.15, you can likely skip the extra minor upgrade step and move directly to creating the Blue/Green Deployment to version 17.x. This will be the most efficient path with the least amount of total downtime.

re:Post Agent · Answer

Let me address your questions about the minor version upgrade for your Aurora PostgreSQL 14.15 cluster:

**1. Zero-Downtime Patching (ZDP) and In-Place Minor Version Upgrade**

Yes, Zero-Downtime Patching (ZDP) is the underlying technology used during in-place minor version upgrades. When you perform an in-place minor version upgrade using the steps you described (Modify → Select DB engine version → Apply immediately), ZDP is automatically applied if your version supports it. Since you're running Aurora PostgreSQL 14.15, which is well beyond version 14.3.3 (when ZDP was introduced), your upgrade will utilize ZDP to minimize downtime.

**2. ZDP Procedure**

You don't need a separate procedure for ZDP—it's automatically used during the standard minor version upgrade process. The steps you outlined are correct:
- Select your database cluster and click Modify
- Under DB engine version, choose your target minor version
- Select "Apply immediately" (or schedule during maintenance window)

The documentation section you referenced provides additional context about ZDP's behavior and limitations, but the upgrade procedure itself remains the same whether ZDP is involved or not. ZDP works behind the scenes to minimize impact during the upgrade.

**3. Reader Instance Requirement**

While ZDP can work with single-instance clusters (writer only), having at least one reader instance can help minimize downtime further. ZDP upgrades instances sequentially, and with a reader present, the system can perform a failover to maintain availability. However, this is not strictly required for ZDP to function. For your use case, if minimizing downtime is critical before proceeding to the Blue/Green deployment for the major version upgrade, adding a temporary reader instance would be beneficial but not mandatory.

Keep in mind that even with ZDP, brief connection interruptions may occur, so it's recommended to perform upgrades during periods of low traffic and ensure your applications use connection retry logic with exponential backoff.  
**Sources**  
[Performing a minor version upgrade - Amazon Aurora](https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/USER_UpgradeDBInstance.PostgreSQL.MinorUpgrade.html)  
[Upgrading Amazon Aurora PostgreSQL DB clusters - Amazon Aurora](https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/USER_UpgradeDBInstance.PostgreSQL.html)

Minor version upgrade for Aurora Postgresql version 14.x

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