diff --git a/_examples/MariaDb/main.tf b/_examples/MariaDb/main.tf
new file mode 100644
index 0000000..acd0623
--- /dev/null
+++ b/_examples/MariaDb/main.tf
@@ -0,0 +1,92 @@
+provider "aws" {
+  region = "ap-south-1"
+}
+
+module "vpc" {
+  source  = "clouddrove/vpc/aws"
+  version = "0.15.0"
+
+  name        = "vpc"
+  environment = "test"
+  label_order = ["environment", "name"]
+
+  cidr_block = "10.0.0.0/16"
+}
+
+module "private_subnets" {
+  source  = "clouddrove/subnet/aws"
+  version = "0.15.3"
+
+  name        = "subnets"
+  environment = "test"
+  label_order = ["environment", "name"]
+
+  availability_zones = ["ap-south-1a", "ap-south-1b"]
+  vpc_id             = module.vpc.vpc_id
+  type               = "public-private"
+  igw_id             = module.vpc.igw_id
+  cidr_block         = module.vpc.vpc_cidr_block
+  ipv6_cidr_block    = module.vpc.ipv6_cidr_block
+}
+
+module "security_group" {
+  source  = "clouddrove/security-group/aws"
+  version = "0.15.0"
+
+  name          = "security-group"
+  environment   = "test"
+  protocol      = "tcp"
+  label_order   = ["environment", "name"]
+  vpc_id        = module.vpc.vpc_id
+  allowed_ip    = ["0.0.0.0/0"]
+  allowed_ports = [3306]
+}
+
+
+module "mariadb" {
+  source = "../../"
+
+  name        = "sg"
+  application = "clouddrove"
+  environment = "test"
+  label_order = ["environment", "name"]
+
+  engine            = "mariadb"
+  engine_version    = "10.6.7"
+  instance_class    = "db.t2.small"
+  allocated_storage = 50
+
+  # kms_key_id        = "arm:aws:kms:<region>:<accound id>:key/<kms key id>"
+
+  # DB Details
+  database_name = "test"
+  username      = "user"
+  password      = "esfsgcGdfawAhdxtfjm!"
+  port          = "3306"
+
+  vpc_security_group_ids = [module.security_group.security_group_ids]
+
+  maintenance_window = "Mon:00:00-Mon:03:00"
+  backup_window      = "03:00-06:00"
+  multi_az           = false
+
+  family = "mariadb10.6"
+  # disable backups to create DB faster
+  backup_retention_period = 0
+
+  enabled_cloudwatch_logs_exports = ["audit", "general"]
+
+  # DB subnet group
+  subnet_ids          = module.private_subnets.public_subnet_id
+  publicly_accessible = true
+
+  # DB parameter group
+
+  # DB option group
+  major_engine_version = "10.6"
+
+  # Snapshot name upon DB deletion
+
+  # Database Deletion Protection
+  deletion_protection = false
+}
diff --git a/_examples/PostgreSQL/main.tf b/_examples/PostgreSQL/main.tf
new file mode 100644
index 0000000..709d030
--- /dev/null
+++ b/_examples/PostgreSQL/main.tf
@@ -0,0 +1,94 @@
+provider "aws" {
+  region = "ap-south-1"
+}
+
+module "vpc" {
+  source  = "clouddrove/vpc/aws"
+  version = "0.15.0"
+
+  name        = "vpc"
+  environment = "test"
+  label_order = ["environment", "name"]
+
+  cidr_block = "10.0.0.0/16"
+}
+
+module "private_subnets" {
+  source  = "clouddrove/subnet/aws"
+  version = "0.15.3"
+
+  name        = "subnets"
+  environment = "test"
+  label_order = ["name", "environment"]
+
+  nat_gateway_enabled = true
+
+  availability_zones              = ["ap-south-1a", "ap-south-1b"]
+  vpc_id                          = module.vpc.vpc_id
+  type                            = "public-private"
+  igw_id                          = module.vpc.igw_id
+  cidr_block                      = module.vpc.vpc_cidr_block
+  ipv6_cidr_block                 = module.vpc.ipv6_cidr_block
+  assign_ipv6_address_on_creation = false
+}
+
+
+module "security_group" {
+  source  = "clouddrove/security-group/aws"
+  version = "0.15.0"
+
+  name          = "security-group"
+  environment   = "test"
+  protocol      = "tcp"
+  label_order   = ["environment", "name"]
+  vpc_id        = module.vpc.vpc_id
+  allowed_ip    = ["0.0.0.0/0"]
+  allowed_ports = [5432]
+}
+
+module "postgresql" {
+  source = "../../"
+
+  name        = "sg"
+  application = "clouddrove"
+  environment = "test"
+  label_order = ["environment", "name"]
+
+  engine            = "postgres"
+  engine_version    = "14.1"
+  instance_class    = "db.t3.medium"
+  allocated_storage = 50
+  storage_encrypted = true
+  # kms_key_id        = "arm:aws:kms:<region>:<accound id>:key/<kms key id>"
+  family = "postgres14"
+  # DB Details
+  database_name = "test"
+  username      = "dbname"
+  password      = "esfsgcGdfawAhdxtfjm!"
+  port          = "5432"
+
+  vpc_security_group_ids = [module.security_group.security_group_ids]
+
+  maintenance_window = "Mon:00:00-Mon:03:00"
+  backup_window      = "03:00-06:00"
+  multi_az           = false
+
+
+  # disable backups to create DB faster
+  backup_retention_period = 0
+
+  enabled_cloudwatch_logs_exports = ["postgresql", "upgrade"]
+
+  # DB subnet group
+  subnet_ids          = module.private_subnets.public_subnet_id
+  publicly_accessible = true
+
+  # DB option group
+  major_engine_version = "14"
+
+  # Snapshot name upon DB deletion
+
+  # Database Deletion Protection
+  deletion_protection = false
+
+}
diff --git a/_examples/complete-mysql/main.tf b/_examples/complete-mysql/main.tf
index 52d557f..a7f2aaa 100644
--- a/_examples/complete-mysql/main.tf
+++ b/_examples/complete-mysql/main.tf
@@ -15,13 +15,13 @@ module "vpc" {
 
 module "subnets" {
   source  = "clouddrove/subnet/aws"
-  version = "0.15.0"
+  version = "0.15.3"
 
   name        = "subnets"
   environment = "test"
   label_order = ["environment", "name"]
 
-  availability_zones = ["ap-south-1a", "ap-south-1b", "ap-south-1c"]
+  availability_zones = ["ap-south-1a", "ap-south-1b"]
   vpc_id             = module.vpc.vpc_id
   type               = "public"
   igw_id             = module.vpc.igw_id
@@ -91,7 +91,6 @@ module "mysql" {
   # Database Deletion Protection
   deletion_protection = false
 
-
   parameters = [
     {
       name  = "character_set_client"
diff --git a/_examples/oracle_db/main.tf b/_examples/oracle_db/main.tf
index 32c8776..51bdd71 100644
--- a/_examples/oracle_db/main.tf
+++ b/_examples/oracle_db/main.tf
@@ -1,5 +1,5 @@
 provider "aws" {
-  region = "eu-west-1"
+  region = "ap-south-1"
 }
 
 module "vpc" {
@@ -23,7 +23,7 @@ module "private_subnets" {
 
   nat_gateway_enabled = true
 
-  availability_zones              = ["eu-west-1a", "eu-west-1b"]
+  availability_zones              = ["ap-south-1a", "ap-south-1b"]
   vpc_id                          = module.vpc.vpc_id
   type                            = "public-private"
   igw_id                          = module.vpc.igw_id
@@ -43,7 +43,7 @@ module "security_group" {
   label_order   = ["environment", "name"]
   vpc_id        = module.vpc.vpc_id
   allowed_ip    = ["0.0.0.0/0"]
-  allowed_ports = [3306]
+  allowed_ports = [1521]
 }
 
 module "oracle" {
@@ -58,9 +58,9 @@ module "oracle" {
   engine_version    = "19.0.0.0.ru-2021-10.rur-2021-10.r1"
   instance_class    = "db.t3.medium"
   allocated_storage = 50
-
+  storage_encrypted = true
   # kms_key_id        = "arm:aws:kms:<region>:<accound id>:key/<kms key id>"
-
+  family = "oracle-se2-19"
   # DB Details
   database_name = "test"
   username      = "admin"
@@ -82,18 +82,12 @@ module "oracle" {
   # DB subnet group
   subnet_ids          = module.private_subnets.public_subnet_id
   publicly_accessible = true
-
-  # DB parameter group
-  parameter_group_name = "default.oracle-se2-19"
-  option_group_name    = "default:oracle-se2-19"
-
   # DB option group
-  major_engine_version = "12.1"
+  major_engine_version = "19"
 
   # Snapshot name upon DB deletion
 
   # Database Deletion Protection
   deletion_protection = false
 
-
 }
diff --git a/_examples/replica-mysql/main.tf b/_examples/replica-mysql/main.tf
index 339a74f..c639f9a 100644
--- a/_examples/replica-mysql/main.tf
+++ b/_examples/replica-mysql/main.tf
@@ -15,7 +15,7 @@ module "vpc" {
 
 module "subnets" {
   source  = "clouddrove/subnet/aws"
-  version = "0.15.0"
+  version = "0.15.3"
 
   name        = "subnets"
   environment = "test"
@@ -142,7 +142,7 @@ module "master" {
 module "replica" {
   source = "../../"
 
-  identifier = "demodb-replica-mysql"
+  #  identifier = "demodb-replica-mysql"
 
   # Source database. For cross-region use this_db_instance_arn
   replicate_source_db = module.master.id
diff --git a/main.tf b/main.tf
index 753ea1e..a357a50 100644
--- a/main.tf
+++ b/main.tf
@@ -14,67 +14,136 @@ module "labels" {
   label_order = var.label_order
 }
 
-resource "aws_db_subnet_group" "main" {
+locals {
+  family                                = coalesce(var.family, join(local.family_separator, [var.engine, local.major_version_substring]))
+  family_separator                      = local.is_mssql || local.is_oracle || local.is_postgres || local.is_mariadb ? "-" : ""
+  major_version_substring               = local.is_mssql ? substr(local.major_version, 0, length(local.major_version) - 1) : local.major_version
+  is_mssql                              = local.engine_class == "sqlserver"
+  is_oracle                             = local.engine_class == "oracle"
+  is_mariadb                            = local.engine_class == "mariadb"
+  is_postgres                           = local.engine_class == "postgres"
+  major_version                         = join(".", local.version_chunk[0])
+  engine_class                          = element(split("-", var.engine), 0)
+  version_chunk                         = chunklist(split(".", local.engine_version), local.is_single_major_version ? 1 : 2)
+  engine_version                        = coalesce(var.engine_version, local.engine_defaults[local.engine_class]["version"])
+  options                               = []
+  subnet_group                          = length(aws_db_subnet_group.db_subnet_group.*.id) > 0 ? aws_db_subnet_group.db_subnet_group[0].id : var.existing_subnet_group
+  parameter_group                       = length(aws_db_parameter_group.main.*.id) > 0 ? aws_db_parameter_group.main[0].id : var.existing_parameter_group_name
+  option_group                          = length(aws_db_option_group.db_option_group.*.id) > 0 ? aws_db_option_group.db_option_group[0].id : var.existing_option_group_name
+  performance_insights_enabled          = var.performance_insights_retention_period == 0 ? false : true
+  performance_insights_retention_period = var.performance_insights_retention_period > 7 ? 731 : 7
+  storage_size                          = coalesce(var.storage_size, lookup(local.engine_defaults[local.engine_class], "storage_size", 10))
+  license_model                         = lookup(local.engine_defaults[local.engine_class], "license", null)
+  port                                  = coalesce(var.port, lookup(local.engine_defaults[local.engine_class], "port", "3306"))
+
+  is_single_major_version = contains(
+    lookup(local.engine_defaults[local.engine_class], "single_major_version", []),
+    element(split(".", local.engine_version), 0)
+  )
+  engine_defaults = {
+    mariadb = {
+      version = "10.4.13"
+    }
+    mysql = {
+      version = "8.0.21"
+    }
+    oracle = {
+      port                 = "1521"
+      version              = "19.0.0.0.ru-2020-10.rur-2020-10.r1"
+      storage_size         = "100"
+      license              = "license-included"
+      jdbc_proto           = "oracle:thin"
+      single_major_version = ["18", "19"]
+    }
+    postgres = {
+      port                 = "5432"
+      version              = "12.4"
+      jdbc_proto           = "postgresql"
+      single_major_version = ["10", "11", "12"]
+    }
+    sqlserver = {
+      port         = "1433"
+      version      = "15.00.4043.16.v1"
+      storage_size = "200"
+      license      = "license-included"
+      jdbc_proto   = "sqlserver"
+    }
+  }
+  parameter_lookup = var.timezone == "" || local.is_mssql ? "none" : "timezone"
+  parameters = {
+    "none" = []
+    "timezone" = [
+      {
+        name  = local.is_postgres ? "timezone" : "time_zone"
+        value = var.timezone
+      },
+    ]
+  }
+  same_region_replica = var.read_replica && length(split(":", var.source_db)) == 1
+}
+
+resource "aws_db_subnet_group" "db_subnet_group" {
   count = var.enabled ? 1 : 0
 
-  name_prefix = format("subnet%s%s", var.delimiter, module.labels.id)
   description = format("Database subnet group for%s%s", var.delimiter, module.labels.id)
-  subnet_ids  = var.subnet_ids
-  tags = merge(
-    module.labels.tags,
-    {
-      "Name" = format("%s%ssubnet", module.labels.id, var.delimiter)
-    }
-  )
+  #  name_prefix = format("subnet%s%s", var.delimiter, module.labels.id)
+  subnet_ids = var.subnet_ids
+  tags       = module.labels.tags
+
+
+  lifecycle {
+    create_before_destroy = true
+  }
+
 }
 
 resource "aws_db_parameter_group" "main" {
-  count = var.enabled && var.engine == "mysql" ? 1 : 0
+  count = var.enabled ? 1 : 0
 
-  name_prefix = format("subnet%s%s", module.labels.id, var.delimiter)
   description = format("Database parameter group for%s%s", var.delimiter, module.labels.id)
+  name_prefix = format("subnet%s%s", module.labels.id, var.delimiter)
   family      = var.family
 
   dynamic "parameter" {
-    for_each = var.parameters
+    for_each = concat(var.parameters, local.parameters[local.parameter_lookup])
     content {
+      apply_method = lookup(parameter.value, "apply_method", null)
       name         = parameter.value.name
       value        = parameter.value.value
-      apply_method = lookup(parameter.value, "apply_method", null)
     }
   }
 
+  lifecycle {
+    create_before_destroy = true
+  }
+
   tags = merge(
     module.labels.tags,
     {
       "Name" = format("%s%sparameter", module.labels.id, var.delimiter)
     }
   )
-
-  lifecycle {
-    create_before_destroy = true
-  }
 }
 
-resource "aws_db_option_group" "main" {
+resource "aws_db_option_group" "db_option_group" {
   count = var.enabled ? 1 : 0
 
-  name_prefix              = format("subnet%s%s", module.labels.id, var.delimiter)
-  option_group_description = var.option_group_description == "" ? format("Option group for %s", module.labels.id) : var.option_group_description
   engine_name              = var.engine
   major_engine_version     = var.major_engine_version
+  name_prefix              = format("subnet%s%s", module.labels.id, var.delimiter)
+  option_group_description = var.option_group_description == "" ? format("Option group for %s", module.labels.id) : var.option_group_description
 
   dynamic "option" {
-    for_each = var.options
+    for_each = concat(var.options, local.options)
     content {
+      db_security_group_memberships  = lookup(option.value, "db_security_group_memberships", null)
       option_name                    = option.value.option_name
       port                           = lookup(option.value, "port", null)
       version                        = lookup(option.value, "version", null)
-      db_security_group_memberships  = lookup(option.value, "db_security_group_memberships", null)
       vpc_security_group_memberships = lookup(option.value, "vpc_security_group_memberships", null)
 
       dynamic "option_settings" {
-        for_each = lookup(option.value, "option_settings", [])
+        for_each = lookup(option.value, "option_settings", null)
         content {
           name  = lookup(option_settings.value, "name", null)
           value = lookup(option_settings.value, "value", null)
@@ -83,7 +152,9 @@ resource "aws_db_option_group" "main" {
     }
   }
 
-
+  lifecycle {
+    create_before_destroy = true
+  }
   tags = merge(
     module.labels.tags,
     {
@@ -91,16 +162,12 @@ resource "aws_db_option_group" "main" {
     }
   )
 
-
   timeouts {
     delete = lookup(var.option_group_timeouts, "delete", null)
   }
-
-  lifecycle {
-    create_before_destroy = true
-  }
 }
 
+
 resource "aws_db_instance" "this" {
   count = var.enabled ? 1 : 0
 
@@ -109,24 +176,24 @@ resource "aws_db_instance" "this" {
   engine            = var.engine
   engine_version    = var.engine_version
   instance_class    = var.instance_class
-  allocated_storage = var.allocated_storage
+  allocated_storage = local.storage_size
   storage_type      = var.storage_type
-  storage_encrypted = true
+  storage_encrypted = var.storage_encrypted
   kms_key_id        = var.kms_key_id
-  license_model     = var.engine != "mysql" ? "bring-your-own-license" : null
+  license_model     = var.license_model == "" ? local.license_model : var.license_model
 
   name                                = var.database_name
   username                            = var.username
   password                            = var.password
-  port                                = var.port
+  port                                = local.port
   iam_database_authentication_enabled = var.iam_database_authentication_enabled
 
   snapshot_identifier = var.snapshot_identifier
 
   vpc_security_group_ids = var.vpc_security_group_ids
-  db_subnet_group_name   = join("", aws_db_subnet_group.main.*.id)
-  parameter_group_name   = var.engine == "mysql" ? join("", aws_db_parameter_group.main.*.id) : var.parameter_group_name
-  option_group_name      = var.engine == "mysql" ? join("", aws_db_option_group.main.*.id) : var.option_group_name
+  db_subnet_group_name   = join("", aws_db_subnet_group.db_subnet_group.*.id)
+  parameter_group_name   = join("", aws_db_parameter_group.main.*.id)
+  option_group_name      = join("", aws_db_option_group.db_option_group.*.id)
 
   availability_zone   = var.availability_zone
   multi_az            = var.multi_az
@@ -144,15 +211,13 @@ resource "aws_db_instance" "this" {
   final_snapshot_identifier   = module.labels.id
   max_allocated_storage       = var.max_allocated_storage
 
-  performance_insights_enabled          = var.performance_insights_enabled
-  performance_insights_retention_period = var.performance_insights_enabled == true ? var.performance_insights_retention_period : null
+  performance_insights_enabled          = local.performance_insights_enabled
+  performance_insights_retention_period = local.performance_insights_enabled ? local.performance_insights_retention_period : null
 
   backup_retention_period = var.backup_retention_period
   backup_window           = var.backup_window
-
-  character_set_name = var.character_set_name
-
-  ca_cert_identifier = var.ca_cert_identifier
+  character_set_name      = local.is_oracle ? var.character_set_name : null
+  ca_cert_identifier      = var.ca_cert_identifier
 
   enabled_cloudwatch_logs_exports = var.enabled_cloudwatch_logs_exports
 
@@ -166,4 +231,10 @@ resource "aws_db_instance" "this" {
     delete = lookup(var.timeouts, "delete", null)
     update = lookup(var.timeouts, "update", null)
   }
+
+  depends_on = [
+    aws_db_option_group.db_option_group,
+    aws_db_parameter_group.main,
+    aws_db_subnet_group.db_subnet_group,
+  ]
 }
diff --git a/outputs.tf b/outputs.tf
index 549e09b..127f06a 100644
--- a/outputs.tf
+++ b/outputs.tf
@@ -1,4 +1,4 @@
 output "id" {
-  value       = aws_db_option_group.main.*.id
+  value       = aws_db_option_group.db_option_group.*.id
   description = "The ID of the cluster."
 }
diff --git a/variables.tf b/variables.tf
index 122278b..d925dff 100644
--- a/variables.tf
+++ b/variables.tf
@@ -67,12 +67,36 @@ variable "storage_type" {
   default     = "gp2"
   description = "One of 'standard' (magnetic), 'gp2' (general purpose SSD), or 'io1' (provisioned IOPS SSD). The default is 'io1' if iops is specified, 'standard' if not. Note that this behaviour is different from the AWS web console, where the default is 'gp2'."
 }
+variable "existing_subnet_group" {
+  type        = string
+  default     = ""
+  description = "The existing DB subnet group to use for this instance (OPTIONAL)"
+}
 
+variable "existing_parameter_group_name" {
+  type        = string
+  default     = ""
+  description = "The existing parameter group to use for this instance. (OPTIONAL)"
+}
+
+variable "existing_option_group_name" {
+  type        = string
+  default     = ""
+  description = "The existing option group to use for this instance. (OPTIONAL)"
+
+}
 
 variable "kms_key_id" {
-  description = "The ARN for the KMS encryption key. If creating an encrypted replica, set this to the destination KMS ARN. If storage_encrypted is set to true and kms_key_id is not specified the default KMS key created in your account will be used"
   type        = string
   default     = ""
+  description = "The ARN for the KMS encryption key. If creating an encrypted replica, set this to the destination KMS ARN. If storage_encrypted is set to true and kms_key_id is not specified the default KMS key created in your account will be used"
+
+}
+variable "storage_encrypted" {
+  type        = bool
+  default     = true
+  description = "The ARN for the KMS encryption key. If creating an encrypted replica, set this to the destination KMS ARN. If storage_encrypted is set to true and kms_key_id is not specified the default KMS key created in your account will be used"
+
 }
 
 variable "replicate_source_db" {
@@ -91,7 +115,6 @@ variable "license_model" {
   type        = string
   default     = ""
   description = "License model information for this DB instance. Optional, but required for some DB engines, i.e. Oracle SE1"
-
 }
 
 variable "iam_database_authentication_enabled" {
@@ -122,14 +145,12 @@ variable "instance_class" {
   type        = string
   default     = ""
   description = "The instance type of the RDS instance"
-
 }
 
 variable "database_name" {
   type        = string
   default     = "test"
   description = "database name for the master DB"
-
 }
 
 variable "username" {
@@ -155,13 +176,23 @@ variable "vpc_security_group_ids" {
   default     = []
   description = "List of VPC security groups to associate"
 }
-
+variable "read_replica" {
+  description = "Specifies whether this RDS instance is a read replica."
+  type        = string
+  default     = false
+}
 variable "db_subnet_group_name" {
   type        = string
   default     = ""
   description = "Name of DB subnet group. DB instance will be created in the VPC associated with the DB subnet group. If unspecified, will be created in the default VPC"
 }
 
+variable "source_db" {
+  default     = ""
+  type        = string
+  description = "The ID of the source DB instance.  For cross region replicas, the full ARN should be provided"
+}
+
 variable "parameter_group_description" {
   type        = string
   default     = ""
@@ -211,6 +242,11 @@ variable "monitoring_role_arn" {
   description = "The ARN for the IAM role that permits RDS to send enhanced monitoring metrics to CloudWatch Logs. Must be specified if monitoring_interval is non-zero."
 }
 
+variable "storage_size" {
+  type        = string
+  default     = ""
+  description = "Select RDS Volume Size in GB."
+}
 
 variable "monitoring_role_name" {
   type        = string
@@ -391,7 +427,7 @@ variable "performance_insights_enabled" {
 
 variable "performance_insights_retention_period" {
   type        = number
-  default     = 7
+  default     = 0
   description = "The amount of time in days to retain Performance Insights data. Either 7 (7 days) or 731 (2 years)."
 }
 
diff --git a/versions.tf b/versions.tf
index 5e90985..4ce185f 100644
--- a/versions.tf
+++ b/versions.tf
@@ -1,4 +1,10 @@
 # Terraform version
 terraform {
   required_version = ">= 0.12"
+  required_providers {
+    aws = {
+      source  = "hashicorp/aws"
+      version = ">= 3.1.15"
+    }
+  }
 }