DBStack.ts

import { Table, StackContext, RDS } from "sst/constructs";

import * as rds from "aws-cdk-lib/aws-rds";
import * as secretsManager from "aws-cdk-lib/aws-secretsmanager";
import * as path from 'path';
import { Fn } from "aws-cdk-lib";

export function DBStack({ stack, app }: StackContext) {
    
    // Create a DynamoDB table
    const table = new Table(stack, "Counter", {
        fields: {
        counter: "string",
        },
        primaryIndex: { partitionKey: "counter" },
    });

    // Create an RDS database
    const mainDBLogicalName = "MainDatabase";
    // Define output/export attributes names
    const dbSecretArnOutputName = "DBSecretArn";
    const dbClusterIdentifierOutputName = "DBClusterIdentifier";
    // create db variable that will hold the RDS db construct
    var db:RDS

    if (app.stage == "prod") {
        db = new RDS(stack, mainDBLogicalName, {
            engine: "mysql5.7",
            defaultDatabaseName: "maindb",
            migrations: [".","packages","db-migrations"].join(path.sep),
        });

        // Export db secret arn and cluster identifier to be used by other stages
        stack.addOutputs({
            [dbSecretArnOutputName] : {
                value: db.secretArn,
                exportName: dbSecretArnOutputName,
            },
            [dbClusterIdentifierOutputName] : {
                value: db.clusterIdentifier,
                exportName: dbClusterIdentifierOutputName,
            },
        });
    } else {
        // Import the existing secret from the exported value
        const existing_secret = secretsManager.Secret.fromSecretCompleteArn(stack, "ExistingSecret", Fn.importValue(dbSecretArnOutputName));
        // Create an SST resource for the existing DB (does not create a new DB, references the existing one)
        db = new RDS(stack, "ExistingDatabase", {
            engine: "mysql5.7",
            defaultDatabaseName: "maindb",
            migrations: [".","packages","db-migrations"].join(path.sep),
            cdk: {
                cluster: rds.ServerlessCluster.fromServerlessClusterAttributes(stack, "ExistingCluster", {
                    // Import the existing cluster identifier from the exported value
                    clusterIdentifier: Fn.importValue(dbClusterIdentifierOutputName),
                    secret: existing_secret,
                }),
                secret: existing_secret,
            },
        });
    }

    return {table, db};
}