Building highly resilient applications with on-premises interdependencies using AWS Local Zones

This blog post is written by Rachel Rui Liu, Senior Solutions Architect.

AWS Local Zones are a type of infrastructure deployment that places compute, storage, database, and other select AWS services close to large population and industry centers.

Following the successful launch of the AWS Local Zones in 16 US cities since 2019, in Feb 2022, AWS announced plans to launch new AWS Local Zones in 32 metropolitan areas in 26 countries worldwide.

With Local Zones, we’ve seen use cases in two common categories.

The first category of use cases is for workloads that require extremely low latency between end-user devices and workload servers. For example, let’s consider media content creation and real-time multiplayer gaming. For these use cases, deploying the workload to a Local Zone can help achieve down to single-digit milliseconds latency between end-user devices and the AWS infrastructure, which is ideal for a good end-user experience.

This post will focus on addressing the second category of use cases, which is commonly seen in an enterprise hybrid architecture, where customers must achieve low latency between AWS infrastructure and existing on-premises data centers.  Compared to the first category of use cases, these use cases can tolerate slightly higher latency between the end-user devices and the AWS infrastructure. However, these workloads have dependencies to these on-premises systems, so the lowest possible latency between AWS infrastructure and on-premises data centers is required for better application performance. Here are a few examples of these systems:

• Financial services sector mainframe workloads hosted on premises serving regional customers.
• Enterprise Active Directory hosted on premise serving cloud and on-premises workloads.
• Enterprise applications hosted on premises processing a high volume of locally generated data.

For workloads deployed in AWS, the time taken for each interaction with components still hosted in the on-premises data center is increased by the latency. In turn, this delays responses received by the end-user. The total latency accumulates and results in suboptimal user experiences.

By deploying modernized workloads in Local Zones, you can reduce latency while continuing to access systems hosted in on-premises data centers, thereby reducing the total latency for the end-user. At the same time, you can enjoy the benefits of agility, elasticity, and security offered by AWS, and can apply the same automation, compliance, and security best practices that you’ve been familiar with in the AWS Regions.

Enterprise workload resiliency with Local Zones

While designing hybrid architectures with Local Zones, resiliency is an important consideration. You want to route traffic to the nearest Local Zone for low latency. However, when disasters happen, it’s critical to fail over to the parent Region automatically.

Let’s look at the details of hybrid architecture design based on real world deployments from different angles to understand how the architecture achieves all of the design goals.

Hybrid architecture with resilient network connectivity

The following diagram shows a high-level overview of a resilient enterprise hybrid architecture with Local Zones, where you have redundant connections between the AWS Region, the Local Zone, and the corporate data center.

Here are a few key points with this network connectivity design:

1. Use AWS Direct Connect or Site-to-Site VPN to connect the corporate data center and AWS Region.
2. Use Direct Connect or self-hosted VPN to connect the corporate data center and the Local Zone. This connection will provide dedicated low-latency connectivity between the Local Zone and corporate data center.
3. Transit Gateway is a regional service. When attaching the VPC to AWS Transit Gateway, you can only add subnets provisioned in the Region. Instances on subnets in the Local Zone can still use Transit Gateway to reach resources in the Region.
4. For subnets provisioned in the Region, the VPC route table should be configured to route the traffic to the corporate data center via Transit Gateway.
5. For subnets provisioned in Local Zone, the VPC route table should be configured to route the traffic to the corporate data center via the self-hosted VPN instance or Direct Connect.

Hybrid architecture with resilient workload deployment

The next examples show a public and a private facing workload.

To simplify the diagram and focus on application layer architecture, the following diagrams assume that you are using Direct Connect to connect between AWS and the on-premises data center.

Example 1: Resilient public facing workload

With a public facing workload, end-user traffic will be routed to the Local Zone. If the Local Zone is unavailable, then the traffic will be routed to the Region automatically using an Amazon Route 53 failover policy.

Here are the key design considerations for this architecture:

1. Deploy the workload in the Local Zone and put the compute layer in an AWS AutoScaling Group, so that the application can scale up and down depending on volume of requests.
2. Deploy the workload in both the Local Zone and an AWS Region, and put the compute layer into an autoscaling group. The regional deployment will act as pilot light or warm standby with minimal footprint. But it can scale out when the Local Zone is unavailable.
3. Two Application Load Balancers (ALBs) are required: one in the Region and one in the Local Zone. Each ALB will dispatch the traffic to each workload cluster inside the autoscaling group local to it.
4. An internet gateway is required for public facing workloads. When using a Local Zone, there’s no extra configuration needed: define a single internet gateway and attach it to the VPC.

If you want to specify an Elastic IP address to be the workload’s public endpoint, the Local Zone will have a different address pool than the Region. Noting that BYOIP is unsupported for Local Zones.

5. Create a Route 53 DNS record with “Failover” as the routing policy.

• For the primary record, point it to the alias of the ALB in the Local Zone. This will set Local Zone as the preferred destination for the application traffic which minimizes latency for end-users.
• For the secondary record, point it to the alias of the ALB in the AWS Region.
• Enable health check for the primary record. If health check against the primary record fails, which indicates that the workload deployed in the Local Zone has failed to respond, then Route 53 will automatically point to the secondary record, which is the workload deployed in the AWS Region.

Example 2: Resilient private workload

For a private workload that’s only accessible by internal users, a few extra considerations must be made to keep the traffic inside of the trusted private network.

The architecture for resilient private facing workload has the same steps as public facing workload, but with some key differences. These include:

1. Instead of using a public hosted zone, create private hosted zones in Route 53 to respond to DNS queries for the workload.
2. Create the primary and secondary records in Route 53 just like the public workload but referencing the private ALBs.
3. To allow end-users onto the corporate network (within offices or connected via VPN) to resolve the workload, use the Route 53 Resolver with an inbound endpoint. This allows end-users located on-premises to resolve the records in the private hosted zone. Route 53 Resolver is designed to be integrated with an on-premises DNS server.
4. No internet gateway is required for hosting the private workload. You might need an internet gateway in the Local Zone for other purposes: for example, to host a self-managed VPN solution to connect the Local Zone with the corporate data center.

Hosting multiple workloads

Customers who host multiple workloads in a single VPC generally must consider how to segregate those workloads. As with workloads in the AWS Region, segregation can be implemented at a subnet or VPC level.

If you want to segregate workloads at the subnet level, you can extend your existing VPC architecture by provisioning extra sets of subnets to the Local Zone.

Although not shown in the diagram, for those of you using a self-hosted VPN to connect the Local Zone with an on-premises data center, the VPN solution can be deployed in a centralized subnet.

You can continue to use security groups, network access control lists (NACLs) , and VPC route tables – just as you would in the Region to segregate the workloads.

If you want to segregate workloads at the VPC level, like many of our customers do, within the Region, inter-VPC routing is generally handled by Transit Gateway. However, in this case, it may be undesirable to send traffic to the Region to reach a subnet in another VPC that is also extended to the Local Zone.

Key considerations for this design are as follows:

1. Direct Connect is deployed to connect the Local Zone with the corporate data center. Therefore, each VPC will have a dedicated Virtual Private Gateway provisioned to allow association with the Direct Connect Gateway.
2. To enable inter-VPC traffic within the Local Zone, peer the two VPCs together.
3. Create a VPC route table in VPC A. Add a route for Subnet Y where the destination is the peering link. Assign this route table to Subnet X.
4. Create a VPC route table in VPC B. Add a route for Subnet X where the destination is the peering link. Assign this route table to Subnet Y.
5. If necessary, add routes for on-premises networks and the transit gateway to both route tables.

This design allows traffic between subnets X and Y to stay within the Local Zone, thereby avoiding any latency from the Local Zone to the AWS Region while still permitting full connectivity to all other networks.

Conclusion

In this post, we summarized the use cases for enterprise hybrid architecture with Local Zones, and showed you:

• Reference architectures to host workloads in Local Zones with low-latency connectivity to corporate data centers and resiliency to enable fail over to the AWS Region automatically.
• Different design considerations for public and private facing workloads utilizing this hybrid architecture.
• Segregation and connectivity considerations when extending this hybrid architecture to host multiple workloads.

Hopefully you will be able to follow along with these reference architectures to build and run highly resilient applications with local system interdependencies using Local Zones.