Understanding VPC links in Amazon API Gateway

If you’re working with AWS and trying to securely expose services inside a VPC without letting them peek out into the public internet, you’re in the right place. Understanding VPC Links in Amazon API Gateway lets you securely connect your APIs to backend services like EC2, ECS, or internal load balancers. Whether you’re building for internal teams, complying with strict data policies, or just aiming for a tighter security posture, this guide will help you understand how private integrations work, how they’re different from private APIs, and the different patterns you can use.

Let’s break it down.

What is Private Integration?

Private Integration in Amazon API Gateway allows you to securely connect your API Gateway with backend resources that are hosted inside a VPC. This is achieved using a VPC Link, which enables the API Gateway to route traffic to services such as EC2, ECS, or internal load balancers (ALB/NLB) without exposing them to the public internet.

Key Points:

• Backend resources stay private inside the VPC.
• VPC Link bridges API Gateway and VPC.
• Suitable for internal microservices, compliance-heavy apps, or sensitive systems.

Difference Between Private API and Private Integration Private Integration in Amazon API Gateway

Understanding the difference between Private API and Private Integration is essential when designing secure, scalable architectures on AWS. Although they sound similar, they serve different purposes and are implemented using different underlying mechanisms. Knowing when to use which can help you avoid misconfigurations and ensure that your API setup aligns with your security and access requirements.

In this section, we’ll break down how these two concepts compare — so you can make an informed decision based on your specific use case.

To make things a little clearer, let’s compare private APIs and private integrations side by side:

Types of Private Integration in Amazon API Gateway (REST vs HTTP APIs)

When setting up private integrations in Amazon API Gateway, it’s important to understand the type of API you’re working with — REST or HTTP — because this determines the type of VPC Link integration available to you. REST APIs are the older, more traditional option, while HTTP APIs are designed to be lightweight and performant, with lower latency and cost.

Each API type has different capabilities, especially when it comes to the kinds of load balancers they support through VPC Link. Let’s take a closer look at how they differ:

Understanding VPC links – REST APIs

When you create a VPC Link for an API Gateway REST API, AWS sets up a secure, private connection using AWS PrivateLink:

1. A VPC endpoint service is created in your account, pointing to a Network Load Balancer (NLB).
2. API Gateway (operated by AWS) automatically creates an interface VPC endpoint in its own VPC to connect to your endpoint service.
3. This forms a private connection from API Gateway to your backend services inside your VPC.
4. Traffic flows through the NLB, which forwards requests to your backend targets (like EC2 instances or containers).

Understanding VPC links – HTTP APIs

HTTP APIs are the newer, faster, and cheaper option in API Gateway. When you use a VPC Link with an HTTP API:

• You don’t need a Network Load Balancer (NLB) or a VPC endpoint service.
• You can connect directly to:
  • Application Load Balancers (ALBs)
  • AWS Cloud Map services
  • Multiple backend targets — all with a single VPC link.

Behind the scenes, AWS creates a private tunnel between API Gateway and your VPC using network interfaces managed by AWS Hyperplane. This keeps traffic private and secure — no public internet is involved.

You can also use security groups to control access, just like with any other VPC resource.

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Types of Private Integration in Amazon API Gateway

Once you’re comfortable with how VPC Links work and which APIs support them, the next step is understanding how to architect them based on your infrastructure. The pattern you choose directly affects your application’s scalability, cost, availability, and most importantly—its security posture.

Each of these VPC Link patterns represents a different architectural setup, determined by factors such as whether your ALB/NLB is internal or external, and whether your subnets are public or private. Let’s dive deeper into each pattern so you can pick the one that fits your needs best.

Depending on your architecture and security needs, there are several patterns you can use when connecting your API Gateway to a backend via VPC Link:

Pattern1: HTTP API – VPC Link (Private Subnets + Internal ALB)

This is the most secure and recommended setup for private integrations using HTTP APIs. The internal ALB ensures no external internet traffic can reach your backend.

• ALB Configuration: Internal ALB deployed in private subnets.
• Subnet Setup: Private subnets with no route to the internet (No IGW/NAT).
• Security Groups: Allow access only from the VPC Link or specific source IPs within the VPC.
• Scalability: Supports auto-scaling backend services (like ECS or EC2).
• Monitoring: Can integrate with CloudWatch and X-Ray for tracing.
• Use Case: Imagine you’re building an internal HR management system used only by employees within your corporate network. The frontend might be hosted on an internal domain (like hr.company.local) and your APIs need to talk to services like ECS tasks or EC2 instances running sensitive business logic (payroll, employee records, etc.). By placing the ALB in private subnets and accessing it through a VPC Link, you ensure the entire system stays isolated from the internet while still benefiting from the scalability of API Gateway.

Pattern 2: HTTP API – VPC Link (Public Subnets + Internal ALB)

In this setup, the ALB is still internal, but deployed in public subnets. This may be necessary if you’re constrained by subnet availability or IP address management.

• ALB Configuration: Internal ALB, despite public subnet placement.
• Subnet Setup: Public subnets with route to IGW, but ALB is not internet-facing.
• Security Caveat: Ensure proper security groups and route tables to maintain private access.
• Use Case: You might be in the middle of migrating a monolithic on-prem application to AWS. Some parts of your infrastructure are still public, such as legacy monitoring tools or staging environments. In this case, placing the ALB in public subnets (but still internal) gives you flexibility during the transition period while still keeping API Gateway traffic private via the VPC Link. This allows teams to test and access backend services without exposing them publicly.
  Not as ideal as private subnets, but still a valid approach if carefully controlled.e public.

Pattern 3: REST API – VPC Link (Internal NLB)

This is the go-to pattern for REST APIs that require secure backend access. NLBs are great for high-throughput, low-latency connections and support static IPs.

• NLB Configuration: Internal, no public IPs, deployed in private subnets.
• Subnet Setup: No internet access, enhancing isolation.
• Health Checks: NLBs rely heavily on healthy targets — configure these carefully.
• Use Case: Consider a financial services platform that runs sensitive transaction processing and compliance logic inside a VPC. These workloads require stable connections and fixed IPs, which NLBs provide. Using a REST API allows for deep request/response customization, while the internal NLB ensures tight network isolation.
• Perfect for REST-based systems that need performance and privacy.

Pattern 4 : REST API – VPC Link (External NLB)

This pattern uses an external NLB, making your backend service reachable from the public internet. It’s typically used in legacy systems where external access is unavoidable.

• NLB Configuration: External with public IPs.
• Security Risk: Backend is internet-facing — strict access controls are crucial.
• Best Practices: Use security groups, IP whitelisting, and consider pairing with AWS WAF.
• Usecase: You’re supporting legacy B2B partners who require fixed IP whitelisting and direct access to your services. These partners are outside your AWS environment, and setting up VPNs or PrivateLink is not feasible. An external NLB serves as the public ingress point, and you use a REST API on top of that for policy enforcement and integration control.

Conclusion

VPC Links in Amazon API Gateway empowers you to expose internal services without compromising on security or scalability. It’s a powerful pattern for building APIs that need to talk to services inside a VPC while keeping everything locked down from public access.

Whether you’re dealing with REST APIs and internal NLBs, or HTTP APIs using internal or external ALBs, the architectural choices you make around VPC Links directly impact performance, maintainability, and security. That’s why understanding VPC Links in Amazon API Gateway is essential—not just for DevOps teams, but for any architect or developer working in AWS.

By implementing these patterns correctly, you’re setting yourself up for scalable and secure integrations that align with modern cloud best practices. So take the time to design thoughtfully, because understanding VPC Links in Amazon API Gateway could be the key to unlocking a secure, high-performance backend architecture.

Happy architecting!

References:

https://aws.amazon.com/blogs/compute/understanding-vpc-links-in-amazon-api-gateway-private-integrations

https://docs.aws.amazon.com/apigateway/latest/developerguide/set-up-private-integration.html

https://docs.aws.amazon.com/apigateway/latest/developerguide/http-api-develop-integrations-private.html

https://cloudnamaste.com/build-apis-with-amazon-api-gateway/