RDS controller: DBInstance creation fails inside DBCluster due to “InvalidParameterCombination: You can’t modify the Database Insights mode”

[gecube]

Summary

When trying to create a DBInstance inside an existing Aurora MySQL DBCluster using the ACK RDS controller, the instance creation fails with the following terminal condition:

api error InvalidParameterCombination: You can't modify the Database Insights mode for DB instances within a DB cluster. To modify the Database Insights mode, you must modify the DB cluster.

The DBCluster itself is created successfully via a Kubernetes manifest.

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Steps to Reproduce

1. Create a DBCluster manifest:

apiVersion: rds.services.k8s.aws/v1alpha1
kind: DBCluster
metadata:
  name: postdeal-uat-2025-11-11
spec:
  dbClusterIdentifier: postdeal-uat-2025-11-11
  databaseName: postdeal
  engine: aurora-mysql
  engineMode: provisioned
  engineVersion: "8.0.mysql_aurora.3.08.2"
  masterUsername: "root"
  masterUserPassword:
    namespace: infra-uat
    name: password
    key: password
  dbSubnetGroupName: "rds-subnet"
  backupRetentionPeriod: 30
  copyTagsToSnapshot: true
  enableCloudwatchLogsExports:
    - audit
    - error
    - general
    - slowquery
  deletionProtection: true

2. Then create a DBInstance manifest referring to the cluster:

apiVersion: rds.services.k8s.aws/v1alpha1
kind: DBInstance
metadata:
  name: postdeal-uat-2025-11-11
spec:
  databaseInsightsMode: standard
  dbInstanceClass: db.r5.large
  dbClusterIdentifier: postdeal-uat-2025-11-11
  dbInstanceIdentifier: postdeal-uat-2025-11-11
  engine: aurora-mysql
  engineVersion: "8.0.mysql_aurora.3.08.2"
  dbSubnetGroupName: "rds-subnet"

3. Observe that the DB instance fails to create. Running:

kubectl describe DBInstance postdeal-uat-2025-11-11

shows:

status:
  conditions:
  - message: 'api error InvalidParameterCombination: You can''t modify the Database
      Insights mode for DB instances within a DB cluster. To modify the Database Insights
      mode, you must modify the DB cluster.'
    status: "True"
    type: ACK.Terminal

---

Expected Behavior

The DBInstance should be successfully created inside the existing Aurora MySQL cluster.

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Actual Behavior

The resource enters a terminal error state and is never created.
The controller seems to apply databaseInsightsMode to a clustered instance, which RDS does not allow.

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Possible Cause / Suggestion

The controller likely includes the DatabaseInsightsMode parameter in the CreateDBInstance API request even when dbClusterIdentifier is specified.
This field should probably be omitted when creating instances that belong to a cluster.

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Environment

• Region: eu-west-2
• Engine: aurora-mysql
• Engine version: 8.0.mysql_aurora.3.08.2

---

Workaround

Remove the line

databaseInsightsMode: standard

from the DBInstance spec.
After removing it, the instance is created successfully.

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