A DB parameter group acts as a container for engine configuration values that apply to all instances associated with that group. Common use cases include setting character encodings, adjusting connection limits, tuning autovacuum behavior in PostgreSQL, and enabling slow query logs.
By default, this module creates a parameter group automatically. You can also reference an existing parameter group or fall back to the AWS-managed default.
Variables
| Variable | Default | Description |
|---|
create_db_parameter_group | true | Whether to create a parameter group. Set to false to use an existing one or the AWS default. |
parameter_group_name | null | Name of the parameter group to create or reference. Defaults to the instance identifier. |
parameter_group_use_name_prefix | true | When true, appends a unique suffix to the name to avoid conflicts. Set to false to use the exact name. |
family | null | The parameter group family. Required when creating a new parameter group (e.g., mysql8.0, postgres17). |
parameters | null | List of parameter objects to apply. |
parameter_group_description | null | Description for the parameter group. |
parameter_group_skip_destroy | null | When true, removes the parameter group from state on destroy without deleting it from AWS. |
The parameters object
Each entry in parameters accepts the following fields, as defined in variables.tf:
parameters = [
{
name = string # Parameter name (required)
value = string # Parameter value (required)
apply_method = optional(string) # "immediate" or "pending-reboot" (optional)
}
]
apply_method is omitted, AWS uses the default for that parameter (usually immediate for dynamic parameters and pending-reboot for static ones).
Usage patterns
Create new
Use existing
AWS default
The module creates a parameter group by default. Provide family and parameters to configure it:module "db" {
source = "terraform-aws-modules/rds/aws"
identifier = "demodb"
engine = "mysql"
engine_version = "8.0"
instance_class = "db.t4g.large"
allocated_storage = 20
# Parameter group
family = "mysql8.0"
parameters = [
{
name = "character_set_client"
value = "utf8mb4"
},
{
name = "character_set_server"
value = "utf8mb4"
}
]
# ... other required variables
}
parameter_group_name = "prod-instance-mysql-8.0"
parameter_group_use_name_prefix = false
parameter_group_name = "prod-instance-mysql-8.0"
# parameter_group_use_name_prefix = true (default)
prod-instance-mysql-8.0-20240101120000000000000001. To reference a parameter group created outside the module, set create_db_parameter_group = false and provide its name:module "db" {
source = "terraform-aws-modules/rds/aws"
identifier = "demodb"
engine = "mysql"
engine_version = "8.0"
instance_class = "db.t4g.large"
allocated_storage = 20
# Reference existing parameter group
create_db_parameter_group = false
parameter_group_name = "prod-instance-mysql-8.0" # must already exist in AWS
# family and parameters are not used when create_db_parameter_group = false
# ... other required variables
}
To use the AWS-managed default parameter group (no custom parameters), disable parameter group creation and omit the name:module "db" {
source = "terraform-aws-modules/rds/aws"
identifier = "demodb"
engine = "mysql"
engine_version = "8.0"
instance_class = "db.t4g.large"
allocated_storage = 20
# Use the AWS default parameter group
create_db_parameter_group = false
# ... other required variables
}
complete-mysql example does for the db_default module variant:module "db_default" {
source = "../../"
identifier = "${local.name}-default"
create_db_option_group = false
create_db_parameter_group = false
engine = "mysql"
engine_version = "8.0"
family = "mysql8.0"
major_engine_version = "8.0"
instance_class = "db.t4g.large"
allocated_storage = 200
db_name = "completeMysql"
username = "complete_mysql"
port = 3306
db_subnet_group_name = module.vpc.database_subnet_group
vpc_security_group_ids = [module.security_group.security_group_id]
maintenance_window = "Mon:00:00-Mon:03:00"
backup_window = "03:00-06:00"
backup_retention_period = 0
tags = local.tags
}
PostgreSQL example
For PostgreSQL, the family format is postgres{major_version}:
module "db" {
source = "terraform-aws-modules/rds/aws"
identifier = "complete-postgresql"
engine = "postgres"
engine_version = "17"
family = "postgres17"
instance_class = "db.t4g.large"
parameters = [
{
name = "autovacuum"
value = 1
},
{
name = "client_encoding"
value = "utf8"
}
]
# ... other required variables
}
Blue/green deployment parameter example
Some parameters require apply_method = "pending-reboot". For example, enabling logical replication in PostgreSQL for blue/green deployments:
parameters = [
{
name = "rds.logical_replication"
value = 1
apply_method = "pending-reboot"
}
]
Family naming reference
| Engine | Family pattern | Example |
|---|
| MySQL | mysql{major}.{minor} | mysql8.0, mysql8.4 |
| MariaDB | mariadb{major}.{minor} | mariadb10.6 |
| PostgreSQL | postgres{major} | postgres14, postgres17 |
| Oracle EE | oracle-ee-{major} | oracle-ee-19 |
| Oracle SE2 | oracle-se2-{major} | oracle-se2-19 |
| SQL Server EX | sqlserver-ex-{major}.{minor} | sqlserver-ex-15.0 |
| SQL Server SE | sqlserver-se-{major}.{minor} | sqlserver-se-15.0 |
Set parameter_group_skip_destroy = true in production to prevent accidental deletion of a parameter group that is associated with multiple instances. The parameter group will be removed from Terraform state but remain in AWS.