Infrastructure monitoring and alerting is the DevOps backbone, delivering real-time visibility into performance, latency, and resource use to prevent outages, cut costs, and refine architecture. Build it with data collection, alerts, and dashboards (Prometheus, Grafana, Datadog/New Relic, Kibana); set clear thresholds, tiered escalation, and test often. Case studies and an e-commerce workflow show faster MTTR and resilient, secure, high-quality apps.