Explanation:

When configuring the Syslog via Azure Monitor Agent (AMA) connector in Microsoft Sentinel , the Data Collection Rule (DCR) determines which Linux system logs are ingested. Syslog messages are filtered based on facility (the subsystem that generated the message) and severity level (priority) .
According to Microsoft's "Collect Syslog data sources using Azure Monitor Agent" documentation:
"Syslog facilities define which type of process generated the log (e.g., authentication, cron, daemon), and log levels define the severity (0=emerg, 1=alert, 2=crit, 3=err, etc.). To minimize data ingestion and cost, select only the facility and the highest severity level required for your investigation." In this scenario:
* You need to collect logs related to App1 , a background process (non-kernel, non-authentication, non- cron). Typically, such custom or application-level processes send logs to LOG_AUTH or LOG_DAEMON , depending on configuration. If App1 is an application that uses authentication or security features, the LOG_AUTH facility is appropriate.
* You must collect only logs with a critical priority , which corresponds to Syslog severity 2 (critical) .
In Syslog terminology, that maps to the LOG_EMERG or "emergency" level and above.
However, to ensure minimum data collection while still capturing critical events, Sentinel's best practice is to configure the Syslog DCR to collect only the specific facility associated with the application and the exact required severity level. For "critical only," LOG_EMERG is the correct choice because it ensures that only the most urgent (critical/emergency) events are ingested, reducing data volume and cost.
# Final Configuration:
Setting
Correct Option
Purpose
Facility
LOG_AUTH
Collects security/authentication-related logs for App1
Log level
LOG_EMERG
Collects only critical/emergency events (priority # 0) to minimize ingestion volume In summary:
Selecting LOG_AUTH and LOG_EMERG satisfies both requirements - capturing only the highest- severity logs relevant to App1 while keeping the ingestion volume minimal, in line with Microsoft Sentinel Syslog DCR configuration guidance.