HealthStatus

JSON representation 
{
  "ipAddress": string,
  "ipv6Address": string,
  "port": integer,
  "instance": string,
  "healthState": enum (HealthState),
  "ipv6HealthState": enum (HealthState),
  "annotations": {
    string: string,
    ...
  },
  "forwardingRuleIp": string,
  "forwardingRule": string,

  // Union field weight_report can be only one of the following:
  "weight": string,
  "weightError": enum (WeightError)
  // End of list of possible types for union field weight_report.
}
Fields
ipAddress

string

For target pool based Network Load Balancing, it indicates the forwarding rule's IP address assigned to this instance. For other types of load balancing, the field indicates VM internal ip.
ipv6Address

string
port

integer

The named port of the instance group, not necessarily the port that is health-checked.
instance

string

URL of the instance resource.
healthState

enum (HealthState)

Health state of the IPv4 address of the instance.
ipv6HealthState

enum (HealthState)

Health state of the IPv6 address of the instance.
annotations

map (key: string, value: string)

Metadata defined as annotations for network endpoint.
forwardingRuleIp

string

A forwarding rule IP address assigned to this instance.
forwardingRule

string

URL of the forwarding rule associated with the health status of the instance.

Union field weight_report.

weight_report can be only one of the following:
weight

string
weightError

enum (WeightError)

WeightError

This indicates why Health Checkers are not reporting a valid backend weight.

Enums
WEIGHT_NONE This is the default value when WeightReportMode is DISABLE, and is also the initial value when WeightReportMode has just updated to ENABLE or DRY_RUN and there has not been sufficient time to parse and report the backend weight.
UNAVAILABLE_WEIGHT This is the value when the accompanied health status is either TIMEOUT (i.e.,the Health Check probe was not able to get a response in time) or UNKNOWN. For the latter, it should be typically because there has not been sufficient time to parse and report the weight for a new backend (which is with 0.0.0.0 ip address). However, it can be also due to an outage case for which the health status is explicitly reset to UNKNOWN.
MISSING_WEIGHT The response to a Health Check probe did not have the HTTP response header field X-Load-Balancing-Endpoint-Weight.
INVALID_WEIGHT The response to a Health Check probe had the HTTP response header field X-Load-Balancing-Endpoint-Weight, but its content was invalid (i.e., not a non-negative single-precision floating-point number in decimal string representation).

HealthState

HealthState enum. Can be HEALTHY or UNHEALTHY.

Enums
HEALTHY
UNHEALTHY