Why is GetMetricData returning an empty set of values? - amazon-web-services

Question

Using the JS AWS SDK and passing the following parameters:
{
"StartTime": 1548111915,
"EndTime": 1549321515,
"MetricDataQueries": [
{
"Id": "m1",
"MetricStat": {
"Metric": {
"MetricName": "NetworkOut",
"Namespace": "AWS/EC2",
"Dimensions": [
{
"Name": "InstanceId",
"Value": "i-[redacted]"
}
]
},
"Period": 300,
"Stat": "Average",
"Unit": "Gigabytes"
}
}
]
}
This is the output:
[
{
"Id": "m1",
"Label": "NetworkOut",
"Timestamps": [],
"Values": [],
"StatusCode": "Complete",
"Messages": []
}
]
The query closely matches the sample request found at https://docs.aws.amazon.com/AmazonCloudWatch/latest/APIReference/API_GetMetricData.html#API_GetMetricData_Examples
I am sure that the instance is a valid instance that has definitely had NetworkOut traffic during that date range.
What reason could account for the lack of elements in Values array?

Answer 1

A better solution was to omit "Unit" altogether, which allowed AWS to choose the appropriate unit, not only in scale but in category.

Answer 2

I tried it and got the same (empty) result as you.
I then changed Gigabytes to Bytes and got a result. So, it could be that you need to reduce your Unit size.
Here's the command I used for the AWS CLI:
aws cloudwatch get-metric-data --start-time 1548111915 --end-time 1549321515 --metric-data-queries '[
{
"Id": "m1",
"MetricStat": {
"Metric": {
"MetricName": "NetworkOut",
"Namespace": "AWS/EC2",
"Dimensions": [
{
"Name": "InstanceId",
"Value": "i-xxx"
}
]
},
"Period": 300,
"Stat": "Average",
"Unit": "Bytes"
}
}
]'

Answer 3

For future inquisitors, there are multiple reasons for which the aws cli silently returns an empty dataset instead of an error, because the input requirements are stricter than the standard user's expectations, but the output requirements are much looser. Examples
wrong unit
incomplete list of dimensions
typos, case-sensitivity, etc
References:
https://aws.amazon.com/premiumsupport/knowledge-center/cloudwatch-getmetricstatistics-data/
https://github.com/grafana/grafana/issues/9852#issuecomment-395023506