A playbook is like a recipe book specifically tailored to address and resolve issues that may occur in an application. Just like following a recipe to cook a meal, a playbook provides a set of predefined steps and actions to take when a particular incident arises.
For example, let's say there's an unexpected spike in the error rate of a web application. The playbook for this scenario could include steps such as checking the server logs, analyzing recent code changes, and scaling up the infrastructure if necessary. By following the playbook, the on-call developer can systematically work through the issue and bring the error rate back to normal.
Playbooks are helpful for known issues that occur repeatedly, but can be useless or even harmful when dealing with a new type of issue, as they can send the on-call team on the wrong path, instead of identifying the root cause of the issue.