About Private Service Connect health for automatic cross-region failover

Private Service Connect health lets service producers define health states that support automatic cross-region failover for service consumers that use Private Service Connect backends. These health states are based on the aggregated health of the service producer's backends (VMs or network endpoints), providing consumers a more accurate failover signal than outlier detection, which infers health from response failures.

To enable cross-region failover, both the service producer and consumer must use a multi-region deployment. When you configure Private Service Connect health, the health state of each regional published service is automatically propagated to the consumer's load balancer. If a service instance in one region becomes unhealthy, the consumer's load balancer stops routing traffic to that service and instead routes traffic to a healthy service instance in an alternate region.

Deployment requirements

To use Private Service Connect health for automatic failover, both the service producer and the service consumer must configure their resources for a multi-region deployment, as described in this section. For more information about requirements for load balancer and backend types, see Specifications.

Producer configuration:

Consumer configuration:

This example shows a consumer global external Application Load Balancer that connects to a service that is published in multiple regions. Accessing a multi-region service with a supported global or cross-regional load balancer lets the service consumer take advantage of Private Service Connect health for automatic cross-region failover (click to enlarge).

Private Service Connect health components

Private Service Connect health uses the following components to support automatic cross-region failover.

Multiple health sources, each with a health aggregation policy, are combined in a composite health check, which updates the Health Destination.

This diagram shows the key components of Private Service Connect health. Health aggregation policies define conditions for health sources to be considered healthy. Health states for individual health sources are combined into a single state by a composite health check, and the result is delivered to a health destination.

Health aggregation policy

A health aggregation policy is a resource that you create to define the conditions that a backend service must meet to be considered healthy. A policy aggregates the health states of a backend service's backends (VMs in an instance group or network endpoints in a NEG), as determined by regular health checks.

A backend service is considered healthy if two configurable conditions are met:

  • Percentage of healthy endpoints: The minimum percentage of backends that must be healthy. The default is 60%.

  • Minimum number of healthy endpoints: The minimum number of backends that must be healthy. The default value is 1.

For example, you can create a policy that specifies a backend service must have at least 75% of its backends healthy and at least three healthy backends. If the number of healthy backends falls below either of those thresholds, the backend service is considered unhealthy.

Health source

A health source is a resource that makes the health of a single backend service available for aggregation as part of a composite health check. When you create a health source, you specify the following:

  • A backend service to monitor
  • A health aggregation policy that determines the backend service's health

The health source uses the conditions defined in the health aggregation policy to determine the health state of the associated backend service.

Composite health check

A composite health check is a resource that aggregates the health states of one or more health sources to produce a single composite health state for a regional published service. The published service is considered healthy if each of the associated health sources are healthy. If any of the health sources are unhealthy, the service is considered unhealthy.

Health destination

A health destination receives the final composite health state from a composite health check. For a published service, the health destination is the forwarding rule of the producer's load balancer. The health state is automatically propagated to consumer load balancers that connect to this forwarding rule.

Specifications

Private Service Connect health has the following specifications.

  • Behavior:

    • The health of individual backends within a backend service is determined by standard health checks.
    • A configurable health aggregation policy determines the overall health state of a backend service based on the health of its individual backends.
    • A composite health check aggregates the health states from one or more backend services that are configured as health sources, creating a composite health state.
    • The composite health state is provided to a health destination, which must be the forwarding rule of a published service.
    • The composite health state is automatically propagated to connected consumer load balancers, where unheatlhy states trigger automatic cross-region failover.

  • Configuration:

Limitations

Private Service Connect health has the following limitations:

  • Composite health states produced by Private Service Connect health are only visible to the consumer load balancer and can't be viewed in logs.
  • All Private Service Connect health resources, including the backend services and forwarding rules they reference, must exist in the same project.
  • You can't use the composite health state of one service as a health source for another service.
  • There is no mode to test a health check configuration that doesn't affect connected consumers. Any configured composite health checks can immediately trigger failover.
  • Private Service Connect health only supports Private Service Connect backends that access published services.

Pricing

There is no additional charge for using Private Service Connect health. However, you are charged for resources and network traffic in your VPC network.

For more information, see VPC pricing.

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