PrivateLink allows you to connect privately to services without exposing traffic to the public internet, which is critical for security, compliance, and enterprise architectures.

However, while the concept sounds simple, there are several design considerations and configuration gotchas that architects often discover the hard way.

In this post we’ll cover:

• What AWS PrivateLink is
• When to use it
• How it works architecturally
• Common configuration mistakes and gotchas

What is AWS PrivateLink?

AWS PrivateLink allows you to privately access services hosted in another VPC, AWS service, or partner service through interface endpoints.

Instead of routing traffic through:

• Internet Gateway
• NAT Gateway
• VPN
• Direct Connect public endpoints

PrivateLink allows communication entirely within the AWS network.

In short:

PrivateLink provides private connectivity to services using private IP addresses inside your VPC.

How AWS PrivateLink Works

At a high level, PrivateLink connects service consumers and service providers.

Components

Service Provider

• Hosts the service
• Usually fronted by a Network Load Balancer (NLB)
• Creates an Endpoint Service

Service Consumer

• Creates an Interface VPC Endpoint
• Receives private ENIs in their subnets
• Connects to the service via private DNS

Traffic Flow

1. Service provider exposes service behind Network Load Balancer
2. Provider creates VPC Endpoint Service
3. Consumer creates Interface Endpoint
4. AWS creates Elastic Network Interfaces (ENIs) in consumer subnets
5. Traffic flows privately inside AWS backbone

When Should You Use PrivateLink?

PrivateLink is ideal when you want secure service consumption without network-level connectivity.

Common use cases:

1️⃣ Access AWS Services Privately

Example:

• S3
• DynamoDB
• Secrets Manager
• KMS

Your workloads can access these services without a NAT gateway or internet access.

2️⃣ SaaS Providers

If you’re offering a SaaS platform:

PrivateLink allows customers to access your service without exposing public endpoints.

Example:

3️⃣ Cross-Account Service Sharing

Organizations often expose internal services across accounts using PrivateLink instead of:

• VPC Peering
• Transit Gateway

4️⃣ Highly Regulated Environments

Industries like:

• Government
• Finance
• Healthcare

often require no internet exposure, making PrivateLink ideal.

PrivateLink vs VPC Peering

PrivateLink is often preferred when you only want to expose a specific service.

Common AWS PrivateLink Gotchas

Even experienced cloud engineers run into these issues.

Let’s walk through the most common ones.

Gotcha #1 — Requires a Network Load Balancer

PrivateLink only supports Network Load Balancers for endpoint services.

This means:

❌ Application Load Balancer not supported
❌ Classic Load Balancer not supported

If your service runs behind an ALB, you’ll need to place an NLB in front of it.

Typical workaround architecture:

Gotcha #2 — One Endpoint Per AZ

Interface endpoints create Elastic Network Interfaces in each AZ.

If you deploy across 3 AZs:

This increases cost.

Gotcha #3 — It Can Get Expensive

PrivateLink pricing includes:

• Hourly endpoint cost
• Data processing cost

For high-throughput workloads, this can become more expensive than NAT Gateway or Transit Gateway.

Always estimate traffic costs before large deployments.

Gotcha #4 — DNS Can Be Tricky

Private DNS works only when enabled and supported by the service.

Common mistakes include:

• Forgetting to enable Private DNS
• Custom DNS servers not resolving AWS zones
• Split-horizon DNS conflicts

Example:

If Private DNS is enabled, the request resolves to the private endpoint IP.

Gotcha #5 — Security Groups Matter

Interface endpoints support security groups.

If misconfigured:

• Traffic silently fails
• Connectivity appears broken

Typical required rules:

Gotcha #6 — Endpoint Policies Can Block Access

PrivateLink supports endpoint policies that restrict access.

Example policy:

If misconfigured, requests may be denied even when networking is correct.

Gotcha #7 — Cross-Account Acceptance Required

For custom services, the provider must accept endpoint connections.

Common troubleshooting issue:

Provider must approve the request.

Gotcha #8 — Health Checks Can Break Connectivity

Since the service sits behind an NLB, NLB health checks must pass.

If health checks fail:

Always verify:

• Target group health
• Health check port
• Security groups

Architecture Example

Typical enterprise architecture using PrivateLink:

Best Practices

Use these best practices when deploying PrivateLink:

✔ Deploy endpoints in multiple AZs
✔ Enable private DNS when possible
✔ Monitor with VPC Flow Logs
✔ Estimate costs before deployment
✔ Use least-privilege endpoint policies
✔ Implement health checks carefully

Final Thoughts

AWS PrivateLink is an extremely powerful tool for building secure, service-oriented architectures in AWS.

It allows organizations to:

• Eliminate internet exposure
• Provide SaaS services securely
• Simplify cross-account access
• Meet strict compliance requirements

However, the networking and DNS components can introduce unexpected operational complexity, so careful design and testing are critical.