Traffic Director load balancing
Traffic Director uses sidecar proxies or proxyless gRPC to deliver global load balancing for your internal microservices. You can deploy internal microservices (sidecar proxy-based or proxyless gRPC-based) with instances in multiple regions. Traffic Director provides health, routing, and backend information to the sidecar proxies or proxyless gRPC, enabling them to perform optimal traffic routing to application instances in multiple cloud regions for a service.
In the following diagram, user traffic enters a Google Cloud
deployment through an external global load balancer. The external load balancer
distributes traffic to the Front End microservice in either
asia-southeast1, depending on the location of the end user.
The internal deployment features three global microservices: Front End, Shopping
Cart, and Payments. Each service runs on managed instance groups (MIGs) in two
asia-southeast1. Traffic Director uses a global
load-balancing algorithm that directs traffic from the user in California to the
microservices deployed in
us-central1. Requests from the user in
Singapore are directed to the microservices in
An incoming user request is routed to the Front End microservice. The service proxy installed on the host with the Front End then directs traffic to the Shopping Cart. The sidecar proxy installed on the host with the Shopping Cart directs traffic to the Payments microservice. In a proxyless gRPC environment, your gRPC application would handle traffic management.
In the following example, if Traffic Director receives health check results
that indicate that the virtual machine (VM) instances running the Shopping Cart
us-central1 are unhealthy, Traffic Director instructs the
sidecar proxy for the Front End microservices to fail over traffic to the Shopping
Cart microservice running in
asia-southeast1. Because autoscaling is
integrated with traffic management in Google Cloud, Traffic Director
notifies the MIG in
asia-southeast1 of the additional traffic, and the MIG
increases in size.
Traffic Director detects that all backends of the Payments microservice are
healthy, so Traffic Director instructs Envoy's proxy for the Shopping Cart to
send a portion of the traffic—up to the customer's configured
asia-southeast1 and overflow the rest to
Load-balancing components in Traffic Director
During Traffic Director setup, you configure several load-balancing components:
- The backend service, which contains configuration values.
- A health check, which provides health checking for the VMs and Google Kubernetes Engine (GKE) Pods in your deployment.
- With the service routing APIs, a
Gatewayresource and a
- With the load balancing APIs, a global forwarding rule, which includes the VIP address, a target proxy, and a URL map.
An xDS API-compatible sidecar proxy (such as Envoy) runs on a client
VM instance or in a Kubernetes Pod. Traffic Director serves as the control
plane and uses xDS APIs to communicate directly with each proxy. In the data
plane, the application sends traffic to the VIP address configured in the
forwarding rule or
Mesh resource. The sidecar proxy or your gRPC application
intercepts the traffic and redirects it to the appropriate backend.
The following diagram shows an application running on Compute Engine VMs or GKE Pods, the components, and the traffic flow in a Traffic Director deployment. It shows Traffic Director and the Cloud Load Balancing resources that are used to determine traffic routing. The diagram shows the older load balancing APIs.
- To learn about configuring advance load balancing features, see Apply advanced load balancing.
- To learn more about service discovery and traffic interception, see Traffic Director service discovery.
- To learn more about Traffic Director, see the Traffic Director overview.