You are collecting metrics and want to trigger email alerts when thresholds are reached. What tools do you use for this?

A common stack for metric collection, threshold evaluation, and email alerting is Prometheus + Alertmanager. Prometheus scrapes metrics from services, stores them in a time‑series database, and allows you to write PromQL queries to define thresholds. Alertmanager receives alerts from Prometheus, deduplicates them, and can route them to email, Slack, PagerDuty, etc. For visualization, Grafana can be used to build dashboards that display the same metrics. If you prefer a SaaS solution, Datadog, New Relic, or Splunk can ingest metrics, provide built‑in alerting, and send email notifications. The key steps are: 1) instrument your application to expose metrics (e.g., /metrics endpoint). 2) configure Prometheus to scrape those endpoints. 3) write alert rules that fire when a metric crosses a threshold. 4) set up Alertmanager to send an email when an alert fires. This pipeline gives you real‑time visibility and automated notification.