如何使用 terraform 制作单 AZ（非 HA）RDS 实例？

Question

在 this AWS 数据库博客中，他们断言

You can set up Amazon RDS in a Single-AZ database (DB) instance or a Multi-AZ DB instance for high availability requirements

而且你可以

...modify existing Single-AZ instances to become Multi-AZ deployments.

此外，

...you can create a Multi-AZ read replica, synchronize it with your Single-AZ DB instance, and then promote it as your primary DB instance to minimize latencies during conversion.

另外，在官方AWS VPC Module there are multiple references to the usage of single_nat_gateway的v1.32中，特别是

If single_nat_gateway = true, then all private subnets will route their Internet traffic through this single NAT gateway.

并且在官方 RDS 模块中，multi_az 默认显示为 false (link)。

尽管如此，我还是收到以下错误

╷
│ Error: DBSubnetGroupDoesNotCoverEnoughAZs: The DB subnet group doesn't meet Availability Zone (AZ) coverage requirement. Current AZ coverage: us-west-2a. Add subnets to cover at least 2 AZs.
│   status code: 400, request id: *****
│ 
│   with module.rds.module.db_subnet_group.aws_db_subnet_group.this[0],
│   on .terraform/modules/rds/modules/db_subnet_group/main.tf line 8, in resource "aws_db_subnet_group" "this":
│    8: resource "aws_db_subnet_group" "this" {

尝试terraform apply此main.tf配置时：

module "rds" {
  source                                = "terraform-aws-modules/rds/aws"
  version                               = "~> 3.4.0"
  identifier                            = "${var.env}-${var.user}-${local.db_name}"
  engine                                = var.postgres.engine
  engine_version                        = var.postgres.engine_version
  family                                = var.postgres.family
  major_engine_version                  = var.postgres.major_engine_version
  instance_class                        = var.postgres.instance_class
  allocated_storage                     = var.postgres.allocated_storage
  max_allocated_storage                 = var.postgres.max_allocated_storage
  storage_encrypted                     = var.postgres.storage_encrypted
  password                              = random_password.password.result
  port                                  = var.postgres.port
  multi_az                              = false
  subnet_ids                            = [data.aws_subnet.priv1.id]
  vpc_security_group_ids                = [module.db_security_group.security_group_id]
  maintenance_window                    = var.postgres.maintenance_window
  backup_window                         = var.postgres.backup_window
  enabled_cloudwatch_logs_exports       = var.postgres.enabled_cloudwatch_logs_exports
  backup_retention_period               = var.postgres.backup_retention_period
  skip_final_snapshot                   = var.postgres.skip_final_snapshot
  deletion_protection                   = var.postgres.deletion_protection
  performance_insights_enabled          = var.postgres.performance_insights_enabled
  performance_insights_retention_period = var.postgres.performance_insights_retention_period
  create_monitoring_role                = var.postgres.create_monitoring_role
  monitoring_role_name                  = "${var.env}-${var.user}-${var.postgres.monitoring_role_name}"
  monitoring_interval                   = var.postgres.monitoring_interval
  snapshot_identifier                   = var.postgres.snapshot_identifier
  iam_database_authentication_enabled   = var.postgres.iam_auth
  apply_immediately                     = true
  tags = {
    Name        = "${var.env}-${var.user}-rds"
    Terraform   = "true"
    Environment = var.env
    Created     = timestamp()
  }
}

在我的 terraform.tfvars 中定义了这个 postgres 变量：

postgres = {
  db_name = "postgres-db"
  # All available versions: https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_PostgreSQL.html#PostgreSQL.Concepts
  engine                                = "postgres"
  engine_version                        = "11.12"
  family                                = "postgres11" # DB parameter group
  major_engine_version                  = "11"         # DB option group
  instance_class                        = "db.t2.micro"
  allocated_storage                     = 100
  max_allocated_storage                 = 200
  storage_encrypted                     = false
  port                                  = 5432
  multi_az                              = false
  maintenance_window                    = "Mon:00:00-Mon:03:00"
  backup_window                         = "03:00-06:00"
  enabled_cloudwatch_logs_exports       = ["postgresql", "upgrade"]
  backup_retention_period               = 0
  skip_final_snapshot                   = true
  deletion_protection                   = false
  performance_insights_enabled          = false
  performance_insights_retention_period = 7
  create_monitoring_role                = true
  monitoring_role_name                  = "monitoring_role"
  monitoring_interval                   = 60
  snapshot_identifier                   = "arn:aws:rds:us-west-2:999999999999:snapshot:rds-ss"
  iam_auth                              = true
}

关于 SO 的类似问题似乎都有主题的答案，即您必须提供多个可用区，这意味着至少有两个子网，如果您手动创建它们作为私有子网 - 那么每个子网都需要自己的 NAT 网关。这似乎是不必要的昂贵和限制，特别是对于开发和测试环境。

如何使用这些组件部署单 az RDS Postgres 实例？

Answer 1

一个数据库子网组必须有多个子网。这是您无法绕过的 RDS 要求。即使您只部署一个实例，如果整个可用区都出现故障，Amazon RDS 也会自动在您指定的其他可用区之一中启动一个新实例。这是您通过 Amazon RDS 自动获得的托管数据库服务之一。

所以即使部署单az实例，也必须在DB子网组中指定多个可用区。

如何使用 terraform 制作单 AZ（非 HA）RDS 实例？

How to make a single-AZ (non-HA) RDS instance with terraform?

high-availability

amazon-web-services

amazon-rds

terraform

terraform-provider-aws