An unknown error on snapshot upgrade for PostgreSQL

Question

Hi, I have a manual snapshot created from a DB instance running on PostgreSQL 10.20 engine. I want to use this snapshot for creating a new DB instance that will run on PostgreSQL 14.2 through Cloud Formation. Since this snapshot is created from a different PostgreSQL version, I need to upgrade it first to 14.2 before I initiate the create operation (the stack creation fails otherwise). The snapshot upgrade fails as well with: 
```
errorCode: InternalFailure
errorMessage: An unknown error occurred
```
I was upgrading the snapshot through AWS CLI (``aws rds modify-db-snapshot`` command) and AWS console, but in both cases, it fails the same way.

Answer

Hi there!

From the notes, I understand that you want to perform a PostgreSQL upgrade from engine 10.20 to 14.2 and you are currently getting an error. Please correct me if I misunderstood.

Please note that if you're creating or updating your CloudFormation stack, you can receive an "Internal Failure" error when an operation on a resource fails. You can also receive this error if your stack fails to deploy, please refer to outlined AWS documentation [1] to help you troubleshoot the issue.

However, since you also mentioned that the snapshot upgrade fails, I replicated the instance on my side with the specifications and managed to upgrade successfully through the AWS CLI.

This is the command I ran:

```

aws rds modify-db-snapshot --db-snapshot-identifier postgresql-cli-snapshot --engine-version 14.2
```

And the result:

```
{
    "DBSnapshot": {
        "DBSnapshotIdentifier": "postgresql-cli-snapshot",
        "DBInstanceIdentifier": "postgresql",
        "SnapshotCreateTime": "2022-07-01T12:02:33.917000+00:00",
        "Engine": "postgres",
        "AllocatedStorage": 100,
        "Status": "upgrading",
 }
```

I hope you find the above information helpful.

Have a great day ahead!

References:
====================
[1] https://aws.amazon.com/premiumsupport/knowledge-center/cloudformation-internal-failure-error/

An unknown error on snapshot upgrade for PostgreSQL

References:

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