Traffic Director limitations with Envoy

This document describes limitations that apply to Traffic Director, including advanced traffic management limitations. For information about limits, see Quotas and limits.

General limitations

The limitations of Traffic Director include the following:

  • Traffic Director only supports Google Cloud APIs. Traffic Director does not support Istio APIs.
  • You can use Traffic Director to configure the following request protocols: HTTP (HTTP/1.1 or HTTP/2), HTTPS, TCP, and gRPC.
  • When you use Envoy as the dataplane proxy, the stream_idle_timeout value defaults to 5 minutes. This is not configurable through Traffic Director.
  • When you use the target TCP proxy resource to configure the TCP request protocol, you cannot use the advanced traffic management features. Advanced traffic management is only available when you configure the data plane to handle HTTP or gRPC requests.

  • Traffic Director supports Shared VPC. Note the following:

    • With the load balancing APIs, a forwarding rule and its associated target proxy, URL map, backend service, and backend must be in a single project, which can be a host or service project. If you have multiple service projects, each service project can have its own set of these resources.
    • With the load balancing APIs, by default, a forwarding rule that references a Shared VPC network is advertised to all Envoy proxies in the host and service projects attached to the host project, as long as these proxies specify the Shared VPC network in their bootstrap/sidecar.env files. To tailor this behavior, use config filtering.
    • You can access Traffic Director only by the service accounts of projects that have at least one forwarding rule with the load-balancing scheme INTERNAL_SELF_MANAGED associated with the Shared VPC network.

  • Traffic Director supports VPC Network Peering with the service routing APIs, but not with the load balancing APIs.

  • Traffic Director does not support server-first protocols.

  • You cannot use Traffic Director with services running in Knative or Google Cloud Serverless Computing.

  • This document discusses Envoy proxies, but you can use any open standard API (xDS) proxy with Traffic Director. However, Google has tested Traffic Director only with the Envoy proxy.

  • To work with Traffic Director, use Envoy version 1.9.1 or later.

  • To use regular expression, use Envoy version 1.12.0 or later. Envoy versions earlier than 1.12.0 do not support regular expression.

  • To ensure that all known security vulnerabilities are mitigated, we recommend that you use the most recent Envoy version. For information about Envoy security advisories, see Envoy Security Advisories.

  • The Google Cloud console does not support hybrid connectivity network endpoint groups (NEGs). To create or delete hybrid connectivity NEGs, use the Google Cloud CLI.

  • Because your data plane handles health checks, you cannot use the Google Cloud console, API, or gcloud CLI to retrieve health check status.

  • Check iptables and ensure that it is set up correctly. For more information about how to configure iptables, see Envoy's notes about configuring HTTP filtering.

    • If you use the Google Cloud console to create virtual machine (VM) instances, some ipv6-related modules are not installed and available before a restart. As a result, iptables.sh fails due to missing dependencies. In such a case, restart the VM and rerun the run.sh script.
    • If you use the gcloud CLI to create Compute Engine VMs, you are not expected to have this problem.

Advanced traffic management limitations

The limitations of advanced traffic management include the following:

  • If the value of BackendService.sessionAffinity is not NONE, and BackendService.localityLbPolicy is set to a load-balancing policy other than MAGLEV or RING_HASH, the session affinity settings do not take effect.
  • The gcloud import command doesn't delete top-level fields of the resource, such as the backend service and the URL map. For example, if a backend service is created with settings for circuitBreakers, you can use a subsequent gcloud import command to update those settings. However, you cannot delete those settings from the backend service. You can delete and recreate the resource itself without the circuitBreakers settings.
  • Import for forwarding rules doesn't work properly; you can't re-import an exported YAML file. The workaround is to export the configuration file, make changes, delete the forwarding rule, and import the configuration file.

Limitations with Service Directory

  • Service Directory and Traffic Director do not guarantee network reachability for clients.

  • A backend service can only reference one of the following:

    • Managed instance group or unmanaged instance group
    • Network endpoint group
    • Service bindings

  • Service Directory services can only be used with global backend services with load-balancing-scheme=INTERNAL_SELF_MANAGED.

  • A Service Directory service that is referenced by a service binding can be deleted. If the underlying Service Directory service to which the backend service is attached is deleted, applications that use Traffic Director cannot send traffic to this service, therefore, requests fail. See Observability and debugging for best practices.

Health checks

When you bind a Service Directory service to a backend service, you cannot configure a health check on the backend service.

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