Traffic Director with internet network endpoint groups

You can configure Traffic Director to use internet network endpoint groups (NEGs) of the type INTERNET_FQDN_PORT. The external service is represented by its fully qualified domain name (FQDN) and port number in the NEG. The NEG can contain only one FQDN:Port pair, and the backend service can contain only one NEG of this type. The FQDN is resolved by using the underlying Virtual Private Cloud (VPC) network's name resolution order.

Expand the Traffic Director service mesh using FQDN backends

The Traffic Director service mesh can route traffic to private services that are reachable by using hybrid connectivity, including named on-premises, multi-cloud, and internet services. The remote service is referenced by its FQDN.

Extending the Traffic Director service mesh to on-premises or multi-cloud locations using FQDN backends over hybrid connectivity.
Extending the Traffic Director service mesh to on-premises or multi-cloud locations using FQDN backends over hybrid connectivity (click to enlarge)

You can also route traffic to services that are reachable over the public internet.

Extending the Traffic Director service mesh to an internet service using FQDN backends.
Extending the Traffic Director service mesh to an internet service using FQDN backends (click to enlarge)

Google Cloud resources and architecture

This section describes the resources and architecture for configuring Traffic Director with an internet NEG.

INTERNET_FQDN_PORT network endpoint group

To route traffic to an external service referenced by its FQDN, use the global internet NEG of the type INTERNET_FQDN_PORT. The NEG contains the FQDN of your service and its port number. Traffic Director programs the FQDN into Envoy proxies by using xDS configuration.

Traffic Director itself does not guarantee name resolution and reachability of the remote endpoints. The FQDN must be resolvable by the name resolution order of the VPC network to which the Envoy proxies are attached, and the resolved endpoints must be reachable from the Envoy proxies.

Health checks

Health checking behavior for network endpoints of the type INTERNET_FQDN_PORT differs from health checking behavior for other types of network endpoints used with Cloud Load Balancing and Traffic Director. While most other network endpoint types use Google Cloud's centralized health checking system, the NEGs used for endpoints in multi-cloud environments (INTERNET_FQDN_PORT and NON_GCP_PRIVATE_IP_PORT) use Envoy's distributed health checking mechanism. Envoy supports the following protocols for health checking:

  • HTTP
  • HTTPS
  • HTTP/2
  • TCP

You can configure health checks by using the Compute Engine APIs.

DNS considerations

There are two distinct considerations regarding DNS:

  • The DNS server that hosts the resource records of your external service.
  • The mode with which the Envoy proxy is configured to use DNS for connection management.

Cloud DNS server

You can create a Cloud DNS managed private zone to host the DNS records in your Google Cloud project. You can also use other features of Cloud DNS, such as forwarding zones, to fetch records from an on-premises DNS server.

Envoy DNS mode

Envoy DNS mode, which is also called service discovery, specifies how the Envoy proxy uses DNS records for managing outbound connections. Traffic Director configures Envoy to use strict DNS mode. Strict DNS mode enables load balancing to all resolved endpoints. It honors health check status and drains connections to endpoints that are unhealthy or no longer resolved by using DNS. You cannot change this mode.

For more information about service discovery, see the Envoy documentation.

Connectivity and routing

If you are routing traffic to a private service, the following are the requirements for the underlying network connectivity:

  • Hybrid connectivity between the VPC network and the on-premises data center or third-party public cloud is established by using Cloud VPN or Cloud Interconnect.
  • VPC firewall rules and routes are correctly configured to establish bi-directional reachability from Envoy to your private service endpoints and, if applicable, to the on-premises DNS server.
  • For successful regional high-availability failover, global dynamic routing must be enabled. For more details, see dynamic routing mode.

If you are routing traffic to an external service that is reachable on the internet, the following are the requirements:

  • The client virtual machine (VM) instances in the VPC network must have an external IP address or Cloud NAT.
  • The default route must be present to egress traffic to the internet.

In both of the preceding cases, traffic uses the VPC network's routing.

Security

FQDN backends are compatible with Traffic Director's security features and APIs. On the outbound connections to your external service, you can configure FQDN in the SNI header by using client TLS policies.

Limitations and considerations

  • Internet NEGs of the type INTERNET_IP_PORT are not supported with Traffic Director.
  • Envoy version 1.15.0 or later is required with FQDN backends.
  • Use the gcloud command-line tool or REST APIs to configure Traffic Director. End-to-end configuration using the Google Cloud Console is not supported.
  • FQDN backends are only supported with Envoy. Proxyless gRPC is not supported.
  • When you use the NEG type INTERNET_FQDN_PORT with Traffic Director, health checks of the remote endpoints are done using Envoy's distributed health checking mechanism. Whenever a new remote endpoint is added, all Envoy proxies start health checking it independently.

    Similarly, when a new Envoy proxy is added to the mesh, it starts checking all the remote endpoints. Therefore, depending on the number of Envoy proxies and remote endpoints in your deployment, the resulting health check mesh might cause significant network traffic and an undue load on the remote endpoints. You can choose not to configure health checks.

  • Health check status is not visible in the Cloud Console for FQDN backends.

  • Health checking that uses the UDP, SSL, and gRPC protocols is not supported.

  • The following health check options are not supported:

    • HTTP/HTTP2/HTTPS health check
      • --proxy-header
      • --response
    • TCP health check
      • --proxy-header
      • --request
      • --response

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