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Introducing Traffic Director: Google's Service Mesh Control Plane

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Traffic Director, a control plane for service meshes, was announced for beta release at Google Cloud Next 19. Traffic Director is Google Cloud Platform's (GCP) fully-managed service mesh control plane that offers resiliency, load balancing, and traffic control capabilities like canary deployments and A/B testing.

Traffic Director provides traffic configuration and control options for proxies in a service mesh data plane. The "data plane" consists of client proxies, which are generally deployed as out-of-process "sidecars" alongside existing services, and are responsible for performing network-level operations and observing all inbound and outbound traffic. Use of the open source Envoy xDS v2 API (referred to as "xDSv2" by Google) enables Traffic Director to operate with any compliant proxy, such as Envoy.

Traffic Director supports both VM-based and containerized services and provides global load balancing across VMs and clusters in multiple regions. By providing health, routing, and backend information to service proxies, Traffic Director optimizes global traffic distribution and sends traffic to the closest service with availability. With Traffic Director, users can deploy clusters in multiple regions and if the health of a cluster nearest to the originating request degrades, traffic is directed to the closest available cluster.

Traffic Director global load balancing [From Traffic Director's Documentation]

As a part of the load balancing solution, Traffic Director centralizes service health checks by offloading the need for individual proxies to check the health of every other service in the cluster (as the number of requests required for this would increase quadratically in relation to the number of services). The aggregated service health information is distributed from the centralized store to each proxy via the Envoy Endpoint Discovery Service (EDS) API.

Traffic Director also monitors the load reported by proxies to determine when auto-scaling needs to occur. When load increases, Traffic Director notifies the autoscaler and waits for it to scale to the required size, minimizing traffic spike response time by reducing the number of steps in the scaling process. This demand-driven auto-scaling reduces the need for pre-warming or contacting the cloud provider.

Traffic Director is a fully managed GCP service promoted as Enterprise ready with a 99.99% SLA guarantee when it reaches general availability (GA). The Traffic Director configuration lets users set custom traffic control policies by applying actions, such as rewrites, redirects, and header transformations, to HTTP match rules. Benefits of Traffic Director, according to Google, include simplified traffic management for services, service resiliency, and seamless scaling with the growth of a user's application.

Traffic Director is currently in beta and not covered by an SLA or deprecation policy and might be subject to backward-incompatible changes. The beta release is currently limited to only supporting HTTP traffic and Google APIs, and Istio APIs are unsupported. Traffic control features such as routing rules and traffic policies are only available in Alpha. To get started with the beta offering, visit the Traffic Director setup guide.

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