What metrics should be monitored to understand the application's status?

To understand the application's state, it is important to monitor the following metrics:

• Performance: response time, request processing time, requests per second (RPS).
• Resource usage: CPU, memory, disk, and network utilization.
• Errors: number of errors (4xx, 5xx), exceptions, and failures.
• Availability: uptime, downtime.
• Logging: log analysis for anomaly detection.
• Business logic metrics: for example, number of active users, transactions, etc.

Monitoring these metrics allows for quick identification of issues and taking measures to maintain the application's stability and performance.