Microsoft Sentinel: Cloud SIEM Fundamentals

What Microsoft Sentinel is

Microsoft Sentinel is Microsoft's cloud-native SIEM and SOAR solution. SIEM stands for security information and event management, and SOAR stands for security orchestration, automation and response. In practice, Sentinel collects logs from across the organization, applies analytics to detect threats and automates incident response.

Because it is cloud-native, it scales elastically without the need to provision and maintain collection infrastructure, which historically was one of the biggest costs of running a traditional SIEM.

How Sentinel works

Sentinel's value flow can be summarized in four movements:

1. Collect data from users, devices, apps and infrastructure through connectors.
2. Detect previously unknown threats with analytics and minimize false positives.
3. Investigate threats at scale with artificial intelligence and proactive hunting.
4. Respond to incidents quickly with built-in orchestration and automation.

Data connectors

Detection quality depends directly on the data ingested. Sentinel offers native connectors for virtually the entire Microsoft ecosystem and for many third-party sources.

An important decision is what to ingest. Collecting everything indiscriminately raises costs without improving detection. The criterion should be: does this log help detect, investigate or prove an incident?

Analytics rules

Analytics rules turn raw data into actionable alerts and incidents. There are different types:

• Built-in template rules, maintained by Microsoft and ready to use.
• Scheduled query rules, written in the Kusto query language for custom scenarios.
• Machine learning anomaly rules, which learn normal behavior and flag deviations.
• Fusion rules, which correlate multiple low-fidelity alerts into a high-fidelity incident.

Start by enabling the built-in templates relevant to your environment before investing in complex custom rules.

From alerts to incidents

One of the biggest challenges in security operations is alert overload. Sentinel groups related alerts into incidents, reducing noise and providing context. Each incident brings the involved entities, a timeline and evidence, letting the analyst quickly grasp the scope.

Effective incident management involves:

1. Triage by severity and confidence.
2. Assignment to a responsible analyst.
3. Investigation using the investigation graph and hunting.
4. Containment and remediation.
5. Closure with classification and lessons learned.

Automation with playbooks

The SOAR side of Sentinel materializes in playbooks, automated flows that respond to incidents. A playbook can, for example, enrich an alert with threat intelligence, disable a compromised account, isolate a device or open a ticket, all without manual intervention.

Automation reduces mean time to respond and frees analysts for higher-value investigative work. Start by automating repetitive, low-risk tasks, evolving to more autonomous responses as confidence grows.

Cost considerations

Sentinel is billed primarily by the volume of data ingested and retained. Good optimization practices include filtering logs at the source, using basic log tables for low-investigative-value data and setting retention policies aligned with regulatory requirements. A well-designed SIEM balances detection coverage and predictable cost.

Key takeaways

• Microsoft Sentinel is cloud-native SIEM and SOAR, with no infrastructure to maintain.
• Ingest data with judgment: every log should help detect, investigate or prove.
• Start with built-in template analytics rules before customizing.
• Incidents group related alerts, reducing noise and providing context.
• Playbooks automate responses, reducing mean time to respond.

RHC, a Microsoft Solutions Partner, designs and operates Sentinel deployments sized to risk and budget, integrating the SIEM with the rest of Defender XDR.