What is the minimum requirement for an application to expose Prometheus metrics?
Prometheus collects metrics by scraping an HTTP endpoint exposed by the target application. Therefore, the only essential requirement for an application to expose metrics to Prometheus is that it serves metrics in the Prometheus text exposition format over HTTP.
This endpoint is conventionally available at /metrics and provides metrics in plain text format (e.g., Content-Type: text/plain; version=0.0.4). The application can run on any operating system, architecture, or network --- as long as Prometheus can reach its endpoint.
It does not need to be Internet-accessible (it can be internal) and is not limited to Linux or any specific bitness.
Verified from Prometheus documentation -- Exposition Formats, Instrumenting Applications, and Target Scraping Requirements sections.