/rds-db2

RDS for Db2 — Minimum IAM Permissions Reference

Source:

• Workspace: 04-db2-client/minimum-iam-permissions-rds-db2/ (RDS-Db2-IAM-Policy-README.md)
• Bundled policies: ../assets/rds-db2-minimal-iam-policy.json, ../assets/rds-db2-trust-policy.json

Least-privilege IAM for provisioning and managing RDS for Db2 with all in-scope features. Grant only what the workflow needs; never attach a *FullAccess managed policy.

Features the minimal policy covers

The bundled rds-db2-minimal-iam-policy.json scopes permissions for: BYOK (KMS create, import, multi-region replicate), Active Directory integration (Directory Service), S3 database restore and backup, enhanced monitoring (CloudWatch Logs), custom parameter groups (IBM Customer ID and Site ID for BYOL), S3 Db2 auditing (option groups), backup retention, cross-region standby and read replicas, snapshot management, instance modify/delete, and SNS event notifications.

1. Create the role from the trust policy

The trust policy uses an ExternalId so the role can only be assumed by a principal in your account that supplies the agreed external ID (the recommended guard for an IAM-principal-assumed role). Note: aws:SourceArn / aws:SourceAccount are service confused-deputy keys — they are only populated when an AWS service (e.g. rds.amazonaws.com) assumes the role on your behalf, and are absent when an IAM principal calls sts:AssumeRole. Including them here with an AWS (root) principal would make the role unassumable, so this trust policy uses ExternalId only:

{
  "Condition": {
    "StringEquals": {
      "sts:ExternalId": "<unique-external-id>"
    }
  }
}

Replace <account-id> and <unique-external-id> with real values, then create the role:

aws iam create-role \
  --role-name RDS-Db2-Management-Role \
  --assume-role-policy-document file://assets/rds-db2-trust-policy.json

2. Attach the minimal policy

aws iam put-role-policy \
  --role-name RDS-Db2-Management-Role \
  --policy-name RDS-Db2-Minimal-Policy \
  --policy-document file://assets/rds-db2-minimal-iam-policy.json

3. Resource-naming scope patterns

The policy scopes most mutating actions by ARN pattern (with three documented Resource: "*" exceptions noted below), so naming your resources to match the patterns is required:

Only read-only describe actions (for example rds:DescribeDBEngineVersions, ds:DescribeDirectories, ec2:DescribeVpcs) use Resource: "*", because those calls cannot be ARN-scoped. Most mutating statements are ARN-pattern-scoped. iam:PassRole is limited to the rds-* / -rds- / -db2- role patterns and further constrained by an iam:PassedToService condition (rds.amazonaws.com, monitoring.rds.amazonaws.com) so a matching role can only be passed to RDS, not to arbitrary services such as Lambda or EC2.

Documented Resource: "*" exceptions on mutating actions. Three statements intentionally keep Resource: "*" on mutating actions because AWS does not support practical resource-level scoping for them at creation time:

• VPCNetworking — ec2:CreateSecurityGroup and the ec2:Authorize/RevokeSecurityGroupIngress/Egress actions. A security group ARN does not exist until after CreateSecurityGroup runs, so the create call cannot be ARN-scoped; the authorize/revoke calls are commonly left at "*" alongside it. Narrow these with VPC/security-group condition keys (for example ec2:Vpc) in environments that require it.
• DirectoryServiceIntegration — ds:AuthorizeApplication / ds:UnauthorizeApplication do not support resource-level permissions, so they require Resource: "*".
• KMSNonResourceActions — kms:CreateKey (plus kms:ListKeys / kms:ListAliases). A KMS key ARN does not exist until after CreateKey runs, so the create call cannot be ARN-scoped; the list calls are account-wide and cannot be scoped either. All other KMS actions in the policy (encrypt, decrypt, grant, replicate, tag) remain scoped to key/* and alias/* ARNs.

If your environment mandates stricter scoping, split these statements and apply condition keys or VPC ARNs as your account structure allows.

4. Security notes (Layer 3 least-privilege)

• No *FullAccess managed policies and no service:* wildcard actions — each statement lists explicit action names.
• Minimal Resource: "*" — read-only describe actions use "*" (they cannot be ARN-scoped), and three mutating statements (VPCNetworking security-group create/authorize/revoke, DirectoryServiceIntegration ds:Authorize/UnauthorizeApplication, and KMSNonResourceActions kms:CreateKey) keep "*" because AWS does not support resource-level permissions for them at creation time. Every other mutating statement is ARN-pattern-scoped. See §3 for the full exception rationale.
• External ID required for role assumption. The role is assumed by an IAM principal, so it relies on sts:ExternalId rather than the service-only aws:SourceArn / aws:SourceAccount confused-deputy keys (which are absent for sts:AssumeRole by an IAM principal). For roles a service assumes (for example the Db2 audit role that rds.amazonaws.com assumes), use aws:SourceArn / aws:SourceAccount instead — see db2-audit.md.
• Minimal action set per operation — add actions only when a new workflow needs them.

5. Pre-deploy check with the policy simulator

Validate the role grants the actions you expect (and denies the rest) before relying on it:

aws iam simulate-principal-policy \
  --policy-source-arn arn:aws:iam::<account-id>:role/RDS-Db2-Management-Role \
  --action-names rds:CreateDBInstance \
  --resource-arns arn:aws:rds:us-east-1:<account-id>:db:test-db2

Repeat --action-names for each action a workflow performs (for example rds:ModifyDBInstance, kms:CreateGrant, s3:PutObject) and confirm the decision is allowed.

6. Additional permissions you may need

The minimal policy is intentionally narrow. Add scoped permissions when your deployment uses:

• CloudFormation — if you provision RDS for Db2 through Infrastructure as Code.
• Secrets Manager — if you store master credentials there (preferred over inline passwords); pairs with --manage-master-user-password.
• Lambda — if custom functions participate in provisioning or event handling.

Add each as a separate, ARN-scoped statement rather than widening an existing one.