Production Runbook: Identity, TLS, and Connection Lifecycle
An IAM database token is a SigV4-signed credential used only while a new connection is authenticated. Its 15-minute validity does not impose a 15-minute limit on a session that is already connected. Generate a fresh token when a pool creates a physical connection; do not churn healthy connections every 15 minutes. The SDK or CLI signs the token with the endpoint, port, Region, and database user, so a token generated for the wrong endpoint or user will fail even if the caller has otherwise valid AWS credentials. AWS also states that a custom Route 53 name cannot replace the RDS endpoint when generating the token.
Verify Both Authorization Layers
IAM authorization and database authorization are separate. The caller needs rds-db:connect for an ARN containing the database resource ID and database username, not merely the instance identifier. The matching MySQL account or PostgreSQL role must already exist and still needs the minimum SQL privileges required by the application. Test with the exact runtime role, Region, endpoint, port, and username; an administrator token proves little about the workload identity. Keep the policy scoped to one database resource and one login unless a documented operational requirement justifies a broader resource.
aws rds describe-db-instances --db-instance-identifier my-db --query 'DBInstances[0].DbiResourceId' --output text
aws sts get-caller-identityRequire Certificate Verification
Encryption without server identity verification still leaves room for endpoint impersonation. Install the current Amazon RDS certificate authority bundle and configure the client to verify the certificate and hostname, such as sslmode=verify-full for PostgreSQL or the connector's identity-verification mode for MySQL. Do not place the token in a shell history, process list, application log, exception message, or connection URL that telemetry captures. Tokens are generally at least about 1 KB and can grow with policies and tags, so confirm that drivers, proxies, secret wrappers, and environment-variable handling do not truncate them.
Capacity and Failure Modes
IAM authentication consumes resources on the database host. AWS currently advises reserving roughly 300 to 1000 MiB of additional memory and measuring the RDS process resident memory before and after enablement, especially on burstable instance classes. Use a bounded connection pool or RDS Proxy where appropriate, then load-test connection establishment separately from steady-state query throughput. Common failures are an expired token, invalid or truncated token, temporary AWS credentials that expired before connection, a policy for the wrong database resource ID, clock skew, an unavailable CA certificate, and a PostgreSQL role inheriting rds_iam unexpectedly. For PostgreSQL, IAM authentication takes precedence over password authentication when rds_iam is granted, including for the master user, and IAM cannot be used for replication connections.
Cutover, Monitoring, and Rollback
Roll out to one noncritical workload identity first. Record successful and failed connection counts, pool wait time, database memory, connection setup latency, and authentication error categories. Exercise a connection after deliberately expiring a cached token, revoke rds-db:connect and confirm denial, and verify that the account cannot perform ungranted SQL. Keep a tested break-glass database account in a controlled secret store during migration; rollback means directing the pool to that credential and removing rds_iam from the affected PostgreSQL role or changing the MySQL authentication method through an approved change. Do not assume CloudTrail will provide token-generation evidence: AWS documents that IAM database authentication and generate-db-auth-token activity are not logged there.