gcp create metric health checks from health check logs - google-cloud-platform

Question

I'm trying to create a metric on health check for a backend service (load balancer). I need this metric to trigger alerts on failed health checks.
From: https://cloud.google.com/monitoring/api/v3/kinds-and-types
Emulating string-valued custom metrics
String values in custom metrics are not supported, but you can
replicate string-valued metric functionality in the following ways:
Create a GAUGE metric using an INT64 value as an enum that
maps to a string value. Externally translate the enum to a string
value when you query the metric.
Create a GAUGE metric with a BOOL value and a label whose
value is one of the strings you want to monitor. Use the boolean to
indicate if the value is the active value.
For example, suppose you want to create a string-valued metric called "status" with possible options OK, OFFLINE, or PENDING. You could make a GAUGE metric with a label called status_value. Each update would write three time series, one for each status_value (OK, OFFLINE, or PENDING), with a value of 1 for "true" or 0 for "false".
Using Terraform, I tried this, but not sure if it's really converting the values "UNHEALTHY" and "HEALTHY" to 0/1s. I tried to switch metric_type to GAUGE instead of DELTA, but the error from Terraform said I needed to use DELTA, and DISTRIBUTION is required for the value_type. Has anybody tried the docs above where it says GAUGE metric with BOOL value? Don't we need some kind of map of strings to boolean?
Here is my terraform:
resource "google_logging_metric" "logging_metric" {
name = var.name
filter = "logName=projects/[project_id]/logs/compute.googleapis.com%2Fhealthchecks"
metric_descriptor {
metric_kind = "DELTA"
value_type = "DISTRIBUTION"
labels {
key = "status"
value_type = "STRING"
description = "status of health check"
}
display_name = var.display_name
}
value_extractor = "EXTRACT(jsonPayload.request)"
label_extractors = {
"status" = "EXTRACT(jsonPayload.healthCheckProbeResult.healthState)"
}
bucket_options {
linear_buckets {
num_finite_buckets = 3
width = 1
offset = 1
}
}
}