On-call rotation is a practice commonly used in Engineering/ DevOps teams, where a developer takes turns to be “on-call” during non-business hours, such as weekends, or holidays.
On-call rotations make sure that important applications and services are observed all the time, even when developers aren't available. This keeps the applications reliable and reduces downtime. This is important for teams that work all around the world or promise top-notch SLAs.
On-call engineer is the one who is responsible for handling urgent issues and incidents that occur outside of working hours as mentioned above.
They are responsible for monitoring, troubleshooting, incident management, documentation, communication, and alert response. For example, Google has an alert delivery system, that can dispatch pages via multiple mechanisms (email, SMS, robot call, app) across multiple devices.
Here’s a link to Life of an on-call engineer by Google SRE.
Additionally, you might be interested to know more about Incident Response, Alert Fatigue, and SLOs.
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