RDS DB instances should have multiple AZ enabled

A single-AZ RDS instance goes completely offline when its host fails or the AZ has an outage. Multi-AZ keeps a synchronous standby in a different AZ that AWS promotes automatically, typically completing failover in under two minutes.

The cost is real: Multi-AZ roughly doubles instance cost because AWS runs a second instance. For production databases backing revenue-generating workloads, that trade-off is obvious. For dev/test environments, you may want to explicitly exclude them from this control or accept the finding.

Retrofit consideration

Enabling Multi-AZ on an existing single-AZ instance triggers a modification that may cause a brief I/O suspension (typically under 60 seconds) while the standby is provisioned and initial sync completes. Apply during a maintenance window. Instance costs will approximately double.

Implementation

Choose the approach that matches how you manage Terraform.

Compliance.tfOpen source moduleTerraform resources

Use the compliance.tf module to enforce this control by default. See get started with compliance.tf.

HIPAA Omnibus Rule 2013NIST SP 800-53 Rev 5NIST Cybersecurity Framework v2.0FedRAMP Moderate Baseline Rev 4CIS AWS Benchmark v6.0.0NIST SP 800-171 Rev 2CISA Cyber EssentialsNYDFS Cybersecurity RegulationCIS AWS Benchmark v5.0.0FFIEC Cybersecurity Assessment ToolCCCS Medium Cloud Control ProfileACSC ISM March 2023Title 21 CFR Part 11RBI IT Framework for NBFCsFedRAMP Low Baseline Rev 4HIPAA Security Rule 2003NIST Cybersecurity Framework v1.1NIST SP 800-53 Rev 4

module "rds" {
  source  = "hipaa.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "nist80053.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "nistcsf.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "fedrampmoderate.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "cis.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "nist800171.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "cisacyberessentials.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "nydfs23.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "cisv500.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "ffiec.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "cccsmedium.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "acscism2023.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "cfrpart11.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "rbiitfnbfc.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "fedramplow.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "hipaasecurity2003.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "nistcsfv11.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

module "rds" {
  source  = "nist80053rev4.compliance.tf/terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]
}

If you use terraform-aws-modules/rds/aws, set the right module inputs for this control. You can later migrate to the compliance.tf module with minimal changes because it is compatible by design.

module "rds" {
  source  = "terraform-aws-modules/rds/aws"
  version = ">=7.0.0"

  allocated_storage      = 20
  db_name                = "myapp"
  db_subnet_group_name   = "example-db-subnet-group"
  engine                 = "mysql"
  engine_version         = "8.0.41"
  family                 = "mysql8.0"
  identifier             = "abc123"
  instance_class         = "db.t3.micro"
  major_engine_version   = "8.0"
  password_wo            = "change-me-in-production"
  skip_final_snapshot    = true
  username               = "dbadmin"
  vpc_security_group_ids = ["sg-12345678"]

  multi_az = true
}

Use AWS provider resources directly. See docs for the resources involved: aws_db_instance.

resource "aws_db_instance" "this" {
  allocated_storage               = 20
  enabled_cloudwatch_logs_exports = ["general", "slowquery"]
  engine                          = "mysql"
  identifier                      = "pofix-abc123"
  instance_class                  = "db.t3.micro"
  monitoring_interval             = 60
  monitoring_role_arn             = "arn:aws:iam::123456789012:role/example-role"
  password                        = "ChangeMe123!"
  skip_final_snapshot             = true
  username                        = "dbadmin"

  multi_az = true
}

What this control checks

The control checks whether aws_db_instance has multi_az = true. Omitting the argument defaults it to false, which fails. Aurora handles Multi-AZ differently: you distribute aws_rds_cluster_instance resources across AZs rather than setting a flag on aws_db_instance. This control targets standalone non-Aurora engines: MySQL, PostgreSQL, MariaDB, Oracle, and SQL Server. Set multi_az = true explicitly in your aws_db_instance block.

Common pitfalls

Terraform default is false
Omit multi_az from aws_db_instance and it silently defaults to false. Any module or resource block without an explicit multi_az = true fails this control, regardless of what the developer assumed about the default.
Read replicas are not Multi-AZ standby
An aws_db_instance created with replicate_source_db is a read replica, not a Multi-AZ standby. Read replicas use asynchronous replication and do not provide automatic failover. You still need multi_az = true on the primary instance.
Aurora clusters handled differently
Aurora achieves Multi-AZ by placing aws_rds_cluster_instance resources in different AZs using the availability_zone argument. The multi_az flag on aws_db_instance does not apply to Aurora, so this control may not evaluate Aurora clusters correctly.
Applying to an existing instance causes an I/O pause
Use apply_immediately = false to defer the change to the next maintenance window. Flipping multi_az from false to true on a live instance triggers an in-place modification: AWS takes a snapshot, provisions the standby, and synchronizes. There can be brief I/O suspension during initial sync.
Cost doubles for every enabled instance
Multi-AZ provisions a second instance of the same class. A db.r6g.xlarge at roughly $0.48/hr becomes ~$0.96/hr. Exclude dev and staging environments from enforcement, or budget for them explicitly before rolling this out.

Audit evidence

An auditor will look for AWS Config evaluations showing all RDS instances pass the rds-multi-az-support managed rule. The RDS Console's "Configuration" tab for each instance should show "Multi-AZ: Yes". Programmatic evidence comes from aws rds describe-db-instances filtered on the MultiAZ field. CloudTrail ModifyDBInstance events with MultiAZ parameter changes document when remediation occurred.

For periodic reviews, a compliance report from Security Hub or a CSPM tool listing all RDS instances and their Multi-AZ status is a point-in-time snapshot that can be attached to the control assessment.

Framework-specific interpretation

HIPAA Omnibus Rule 2013: 45 CFR 164.308(a)(7) requires covered entities to implement data backup and disaster recovery procedures as part of their contingency plan. Multi-AZ keeps a synchronous standby in a separate AZ with automatic promotion, directly supporting availability for systems storing ePHI.

NIST SP 800-53 Rev 5: A synchronous standby in a separate AZ satisfies the alternate storage site intent of CP-6 and supports automated recovery under CP-10 without manual intervention.

NIST Cybersecurity Framework v2.0: Multi-AZ supports CSF 2.0 Protect outcomes around infrastructure resilience, specifically the expectation that services remain available through AZ-level disruptions.

FedRAMP Moderate Baseline Rev 4: At the Moderate baseline, CP-10 expects federal systems to recover from disruptions with minimal data loss. Multi-AZ synchronous replication can provide very low RPO for the database tier. FedRAMP assessors will look for evidence this is enabled on production databases.

Tool mappings

Use these identifiers to cross-reference this control across tools, reports, and evidence.

Compliance.tf Control: rds_db_instance_multiple_az_enabled
AWS Config Managed Rule: RDS_MULTI_AZ_SUPPORT
Checkov Check: CKV_AWS_157
Powerpipe Control: aws_compliance.control.rds_db_instance_multiple_az_enabled
Prowler Checks: rds_cluster_multi_az, rds_instance_multi_az
AWS Security Hub Control: RDS.5

Last reviewed: 2026-03-09