How to parse a specific key of a json object and store it in a new field using vector remap language

[rk3094]

Hi,

I am new to vector and VRL. I have a metric thath I am trying to send to GCP cloud monitoring sink. We want to process the metric's value from a json and then set it in a new field. Here is a sample input:
{"name":"some_service.metric_name_sample","tags":{"key1":"val1","key2":"val2"},"kind":"absolute","gauge":{"value":1.0}}

I basically need to fetch the value from gauge and set it as one of the fields inside tags. Like expected output:
{"name":"some_service.metric_name_sample","tags":{"key1":"val1","key2":"val2", "value": 1},"kind":"absolute","gauge":{"value":1.0}}

Is it possible to do it using remap? I thought it would be as simple as:

[transforms.enrich_metrics]
type = "remap"
inputs = ["new_metrics"]
source = '''
.tags.value= .gauge.value
'''
Output : It was same as input i.e. {"name":"some_service.metric_name_sample","tags":{"key1":"val1","key2":"val2"},"kind":"absolute","gauge":{"value":1.0}}

On trying this:

[transforms.enrich_metrics]
type = "remap"
inputs = ["new_metrics"]
source = '''
.tags.value= to_string!(.gauge.value)
'''
Output: {"name":"some_service.metric_name_sample","tags":{"key1":"val1","key2":"val2","value":""},"kind":"absolute","gauge":{"value":1.0}}

It looks like gauge needs to be parsed somehow, I tried parse_json, but that also kind of didn't work. It looks like .gauge is getting null value somehow.

[transforms.enrich_metrics]
type = "remap"
inputs = ["new_metrics"]
source = '''
.tags.value= parse_json!(.gauge.value)
'''
Output : It was same as input i.e. {"name":"some_service.metric_name_sample","tags":{"key1":"val1","key2":"val2"},"kind":"absolute","gauge":{"value":1.0}}

Error: 2023-07-25T11:40:46.827680Z ERROR transform{component_kind="transform" component_id=enrich_metrics component_type=remap component_name=enrich_metrics}: vector::internal_events::remap: Mapping failed with event. error="function call error for \"parse_json\" at (346:365): expected string, got null" error_type="conversion_failed" stage="processing" internal_log_rate_limit=true

Can somebody help me with this? @jszwedko

[rk3094]

Vector version info:
INFO vector: Vector has started. debug="false" version="0.31.0" arch="x86_64" revision="0f13b22 2023-07-06 13:52:34.591204470"

Config:

[sources.vector_metrics_source]
type = "prometheus_scrape"
endpoints = [ "http://some_endpoint:port/metrics" ]

[transforms.filter_metrics]
type = "filter"
inputs = [ "vector_metrics_source" ]
condition = '.name == "some_service.metric_name_sample"'

[transforms.new_metrics]
type = "remap"
inputs = ["filter_metrics"]
source = '''
.tags.key1= "val1"
.tags.key2 = "val2"
'''

[transforms.enrich_metrics]
type = "remap"
inputs = ["new_metrics"]
source = '''
.tags.value= parse_json!(.gauge.value)
'''

[sinks.print]
type = "console"
inputs = ["enrich_metrics"]
encoding.codec = "json"