Traffic Director routing rule maps overview

This document describes routing rule maps and how they manage traffic in Traffic Director deployments.

A routing rule map consists of:

  • A forwarding rule that references a target proxy
  • A target proxy that references a URL map
  • A URL map that contains various routing rules

When you create and configure these resources for Traffic Director, Traffic Director uses the values to create the configuration that it sends to your data plane, including, xDS clients such as Envoy proxies and proxyless gRPC applications. The data plane then handles traffic according to this configuration.

A forwarding rule references a target proxy, and has an IP address and a port. For Traffic Director deployments, the forwarding rule's load balancing scheme must be set to INTERNAL_SELF_MANAGED.

The target proxy, in turn, references a URL map. These three resources combine to form a routing rule map.

A forwarding rule that references a target gRPC proxy with the validateForProxyless field set to TRUE must have its IP address set to 0.0.0.0. When validateForProxyless is set to TRUE, configurations that specify an IP address other than 0.0.0.0 are rejected.

The routing rule map defines how traffic passes from clients to servers inside of a service mesh.

Supported target proxy types

Traffic Director supports the following target proxy types:

  • Target HTTP proxy, which you configure when your clients and servers send or receive HTTP or HTTP/2 traffic.
  • Target gRPC proxy, which you configure when your clients and servers send or receive gRPC traffic. Target gRPC proxies contain a field validateForProxyless, which is generally set to TRUE when you are deploying proxyless gRPC services..

Traffic routing with Traffic Director

When you use Traffic Director with Envoy sidecar proxies, client requests are routed as follows:

  • The request is intercepted by the network stack and redirected to your Envoy sidecar proxy.
  • The Envoy sidecar proxy looks at the request's IP address and port.
  • The IP address and port pair checked against the IP and port specified in any forwarding rules that have the load balancing scheme set to INTERNAL_SELF_MANAGED.
  • If a forwarding rule with a matching IP address and port is found, Envoy looks at the target HTTP or gRPC proxy that the forwarding rule references.
  • Envoy checks the URL map that the target proxy references.
  • Envoy routes the request according to the rules specified in the URL map.

This behavior is different for proxyless gRPC applications. When you configure a gRPC client, you specify the target URI for the service that the client needs to contact. This URI uses the xds name resolver scheme and the hostname:port format, for example xds:///myservice:8080.

When the proxyless gRPC client connects to Traffic Director, Traffic Director sends it information corresponding to the service as follows:

  • Traffic Director looks for forwarding rules with load balancing scheme set to INTERNAL_SELF_MANAGED to find forwarding rules whose port matches the port specified in the target URI.
  • Traffic Director finds the target gRPC or HTTP proxy for each of these forwarding rules.
  • Traffic Director finds the URL maps referenced by these target gRPC or HTTP proxies.
  • Traffic Director checks the host rules in the URL map, which also have the hostname[:port] format, and looks for a match.
  • When a match is found, Traffic Director returns routing rules and service information to the gRPC client.

Note that, if more than one match is found, the behavior is undefined and can lead to unpredictable behavior. This generally happens when the following conditions are both met:

  • The same hostname is used across multiple URL maps.
  • Multiple forwarding rules with the load balancing scheme INTERNAL_SELF_MANAGED specify the same port.

For this reason, we recommend that you do not re-use the same hostname across multiple URL maps that are referenced by forwarding rules specifying the same port.

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