RDS Aurora 5.7层级结构咨询：是否需定义全部相关资源？

Hey Jack, let's clear up this confusion because Aurora's architecture is a bit different from standard single-instance RDS, which is probably where the mix-up is happening.

Core Concepts Breakdown #

First, let's distinguish the three resources you mentioned:

• aws_rds_cluster: This is the foundational component of an Aurora deployment. It manages the shared, distributed storage volume used by all instances in the cluster, plus cluster-wide settings like engine version, parameter groups, backup policies, and the cluster's endpoints (writer endpoint for read/write, reader endpoint for load-balanced read traffic). You must define this for any Aurora cluster—without it, there's no shared storage or cluster coordination.
• aws_rds_cluster_instance: These are the actual compute nodes attached to the Aurora cluster. Each instance can be a writer (primary, read/write) or reader (replica, read-only). All instances share the cluster's underlying storage, so data is automatically synced across them. You must define at least one of these (since a cluster can't run without compute nodes) and can add more for high availability or read scaling.
• aws_db_instance: This resource is for standard, single-instance RDS deployments (like a standalone MySQL or PostgreSQL instance that doesn't use Aurora's shared storage). This has nothing to do with Aurora clusters—if you're building Aurora 5.7, you don't need this resource at all.

Correct Aurora Hierarchy #

Your initial hierarchy was off because aws_db_instance doesn't belong in the Aurora stack. The correct structure for Aurora is:
aws_rds_cluster → aws_rds_cluster_instance

Quick Example (Terraform) #

To make this concrete, here's a minimal valid configuration for an Aurora MySQL 5.7 cluster:

# Define the Aurora cluster (shared storage + cluster settings)
resource "aws_rds_cluster" "aurora_mysql_57" {
  cluster_identifier      = "my-aurora-cluster"
  engine                  = "aurora-mysql"
  engine_version          = "5.7.mysql_aurora.2.11.3" # Match your desired 5.7-compatible version
  master_username         = "db_admin"
  master_password         = "your-secure-password-here" # Use a secret in production!
  database_name           = "my_app_db"
  backup_retention_period = 7
  skip_final_snapshot     = true # Only for testing; disable in production
}

# Define at least one cluster instance (primary writer)
resource "aws_rds_cluster_instance" "aurora_primary" {
  identifier             = "my-aurora-primary"
  cluster_identifier     = aws_rds_cluster.aurora_mysql_57.id
  engine                 = "aurora-mysql"
  engine_version         = "5.7.mysql_aurora.2.11.3"
  instance_class         = "db.t3.small"
  publicly_accessible    = false # Restrict access unless needed
}

Key Takeaway #

If your goal is to create an Aurora 5.7 database:

• Do define both aws_rds_cluster and aws_rds_cluster_instance (you can add multiple instances for replicas)
• Do NOT define aws_db_instance—that's for non-Aurora RDS deployments.

内容的提问来源于stack exchange，提问作者Jack