Microsoft Sentinel and Cribl play important roles in modern log onboarding workflows, but they serve different (and often complementary) purposes. Here’s how each fits into log onboarding, especially when used together:

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Microsoft Sentinel – Log Onboarding

Sentinel is a cloud-native SIEM (Security Information and Event Management). Its log onboarding focuses on:

• Ingesting logs from various sources into Log Analytics (Azure Monitor).
• Using Data Connectors to pull in logs from Microsoft and third-party services (e.g., AWS, Cisco, Palo Alto, Syslog, Windows Event Logs, etc.).
• Schema normalization: Sentinel maps incoming logs to the Common Information Model (CIM) using Microsoft’s schema (e.g., SecurityEvent, Syslog, AzureActivity, CommonSecurityLog).

Key Onboarding Steps in Sentinel:

1. Enable a data connector in the Sentinel portal.
2. Configure the source system to send logs (often via agents like AMA/AMA-DS, Azure Arc, or direct API/syslog).
3. Verify ingestion using KQL queries in Log Analytics.
4. Normalize or enrich data using Data Collection Rules (DCRs) or Parser functions (KQL-based).

⚠️ Limitation: Sentinel’s ingestion can become expensive if you onboard high-volume or unfiltered logs. There’s limited pre-ingestion filtering or transformation.

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Cribl – Log Onboarding & Routing

Cribl (especially Cribl Stream) acts as a data pipeline/observability control plane before logs reach their destination (like Sentinel). It excels at:

• Pre-processing logs: filtering, redacting, sampling, parsing, and enriching.
• Routing decisions: send specific logs to Sentinel, others to Splunk, S3, etc.
• Cost optimization: drop low-value logs before they hit expensive platforms.
• Protocol mediation: normalize protocols (Syslog → JSON, CEF → CEF2, etc.).

Key Onboarding Steps with Cribl:

1. Deploy Cribl Edge or Stream (on-prem or cloud).
2. Configure a Source (e.g., Syslog listener, file tail, Kafka, etc.).
3. Define Routes + Pipelines:
   • Use Functions (e.g., filter, mask, parse_cef) to transform data.
   • Route security-relevant logs to Sentinel; operational logs elsewhere.
4. Send to Sentinel via:
   • HTTP Event Collector (HEC) → mapped to Azure Monitor DCR (via Cribl’s Azure Monitor destination).
   • Or Syslog → AMA → Log Analytics (less common now).

✅ Advantage: Cribl gives you observability into your observability data—you can inspect, test, and replay logs before committing to ingestion.

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Using Cribl + Sentinel Together (Recommended Pattern)

1. Collect logs from endpoints, network devices, cloud services → Cribl Stream.
2. Process in Cribl:
   • Drop noise (e.g., health checks, debug logs).
   • Parse & enrich (e.g., extract src_ip, add asset tags).
   • Redact PII if needed.
3. Route only relevant security logs to Microsoft Sentinel via Cribl’s Azure Monitor destination (which uses DCRs under the hood).
4. Optional: Send full fidelity logs to a low-cost lake (e.g., S3) for compliance.

This combo reduces Sentinel ingestion costs, improves data quality, and provides flexibility for multi-destination architectures.

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Practical Tips for Log Onboarding

• Start with high-value sources: firewall, EDR, cloud audit logs.
• Use DCRs in Azure to route/transform logs after ingestion (limited vs. Cribl’s pre-ingestion power).
• Monitor Cribl’s Stream dashboard to validate parsing and routing before enabling Sentinel alerts.
• Tag logs in Cribl with source_type, environment, etc., to simplify Sentinel hunting.