Multi-Tenant SaaS Environment on AWS using Terraform

Objective

The goal of this project is to design and implement a secure, scalable, and automated multi-tenant SaaS environment using AWS and Terraform. Each tenant will have isolated resources, strict IAM policies, and network segmentation to ensure security and compliance.

Architecture Overview

• VPC & Networking: VPC, Subnets, Security Groups, NACLs, Transit Gateway
• Compute: EC2, ECS Fargate (for microservices), Lambda (for serverless functions)
• Storage: S3 (per-tenant buckets), EFS (shared storage)
• Databases: RDS (per-tenant or shared, depending on isolation level), DynamoDB (for metadata)
• IAM & Security: IAM roles/policies, AWS WAF, Shield, Security Hub
• Monitoring & Logging: CloudWatch, AWS X-Ray, AWS Config, GuardDuty
• CI/CD & Deployment: Terraform, GitHub Actions, AWS CodePipeline

Project Implementation Plan

Step 1: Setup Terraform & AWS Provider

• Define the Terraform provider configuration.
• Use Terraform modules for reusability.

Terraform Provider Example

provider "aws" {
  region = "us-east-1"
}

Step 2: Multi-Tenant VPC Design

Each tenant will have an isolated VPC (strong isolation) or a shared VPC with separate subnets (cost-effective).

VPC Module (Terraform)

module "vpc" {
  source = "terraform-aws-modules/vpc/aws"
  name   = "tenant-vpc"
  cidr   = "10.0.0.0/16"
  
  public_subnets  = ["10.0.1.0/24", "10.0.2.0/24"]
  private_subnets = ["10.0.3.0/24", "10.0.4.0/24"]
  
  enable_dns_support = true
  enable_dns_hostnames = true
}

Networking Considerations:

• Use Transit Gateway for inter-tenant communication.
• Restrict access using NACLs and Security Groups.

Step 3: IAM Roles and Policies for Tenant Isolation

• Each tenant gets a separate IAM role with least privilege access.
• Use AWS Organizations & Service Control Policies (SCP) for account-level restrictions.

resource "aws_iam_role" "tenant_role" {
  name = "tenant-role"
  
  assume_role_policy = jsonencode({
    Version = "2012-10-17"
    Statement = [{
      Effect = "Allow"
      Principal = { Service = "ec2.amazonaws.com" }
      Action = "sts:AssumeRole"
    }]
  })
}

Step 4: Multi-Tenant Database Strategy

We can use:

1. Dedicated RDS for each tenant (strong isolation, higher cost).
2. Single RDS with row-level security using PostgreSQL RLS (cost-effective).

Example: RDS per Tenant

resource "aws_db_instance" "tenant_db" {
  identifier = "tenant-db"
  engine     = "postgres"
  instance_class = "db.t3.micro"
  allocated_storage = 20
  username = "admin"
  password = "supersecurepassword"
  publicly_accessible = false
  vpc_security_group_ids = [aws_security_group.tenant_db_sg.id]
}

Step 5: Multi-Tenant Storage (S3)

Each tenant will have a separate S3 bucket or a shared bucket with IAM-based folder access.

Example: Per-Tenant S3 Bucket

resource "aws_s3_bucket" "tenant_bucket" {
  bucket = "tenant-${var.tenant_id}-data"
}

IAM Policy for S3 Access

resource "aws_iam_policy" "tenant_s3_policy" {
  name        = "TenantS3Policy"
  description = "Allows access to a specific tenant's S3 folder"

  policy = jsonencode({
    Version = "2012-10-17"
    Statement = [{
      Effect = "Allow"
      Action = ["s3:ListBucket"]
      Resource = ["arn:aws:s3:::tenant-${var.tenant_id}-data"]
    },
    {
      Effect = "Allow"
      Action = ["s3:GetObject", "s3:PutObject"]
      Resource = ["arn:aws:s3:::tenant-${var.tenant_id}-data/*"]
    }]
  })
}

Step 6: Multi-Tenant Compute (ECS Fargate)

• Deploy tenant applications using ECS Fargate (serverless containers).
• Use Application Load Balancer (ALB) for routing.

Terraform Configuration for ECS

resource "aws_ecs_cluster" "tenant_cluster" {
  name = "tenant-cluster"
}

Step 7: CI/CD Pipeline (Terraform + GitHub Actions)

• Automate Terraform deployment using GitHub Actions.
• Use AWS CodePipeline for application deployment.

Terraform GitHub Actions Workflow

name: Terraform Deployment

on:
  push:
    branches:
      - main

jobs:
  terraform:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout Repo
        uses: actions/checkout@v2

      - name: Setup Terraform
        uses: hashicorp/setup-terraform@v1
        with:
          terraform_version: 1.3.5

      - name: Terraform Init
        run: terraform init

      - name: Terraform Apply
        run: terraform apply -auto-approve

Step 8: Monitoring & Logging

• Use CloudWatch Logs for tenant logs.
• Enable AWS X-Ray for tracing.

Terraform CloudWatch Logs Configuration

resource "aws_cloudwatch_log_group" "tenant_logs" {
  name = "/aws/ecs/tenant-app"
  retention_in_days = 30
}

Step 9: Security Best Practices

• AWS WAF: Protect against
• Use least privilege access.
• Enable S3, RDS, and EBS encryption.

Project Deployment Steps

1. Set up Terraform modules for VPC, IAM, RDS, S3, and ECS.
2. Initialize and apply Terraform configurations.
3. Deploy CI/CD pipeline to automate deployments.
4. Test tenant isolation by verifying IAM policies & network rules.
5. Monitor and optimize using CloudWatch and X-Ray.

Final Thoughts

• Scalability: Easily add new tenants by reusing Terraform modules.
• Security: Enforces strict IAM and network isolation.
• Automation: CI/CD for application and infrastructure deployment.