Relevant telegraf.conf:

System info:

Telegraf version: 1.10.5

Steps to reproduce:

1. Enable StringAsLabel flag and configure Prometheus client
2. Send metrics which has no numeric field and contains a colon (example: a:b)

Expected behavior:

Metrics are sent without any errors

Actual behavior:

Error happens and metrics are not sent

Additional info:

The issue is that the regex check, as per the data model of Prometheus a label must contain only alphanumeric and underscore but the regex used is ^[a-zA-Z_][a-zA-Z0-9_]*

The above regex returns true for a_b:c because it matches it till b however, this label name is not acceptable by Prometheus.