Microsoft Sentinel: Building a Cloud-Native SOC From Scratch

The Security Operations Center (SOC) has traditionally meant expensive, complex on-premise SIEM solutions requiring dedicated hardware, constant maintenance, and a team just to keep the platform running. Microsoft Sentinel changes this fundamentally.

Why Cloud SIEM?

On-premise SIEM has three fundamental problems:

• Capacity planning — — you have to guess how much data you'll collect in a year and buy hardware accordingly
• Maintenance burden — — updates, patching, and troubleshooting consume time that should go to security
• Scaling challenges — — when data volume grows, you need to buy more hardware

Sentinel eliminates these problems by running on Azure Log Analytics. You pay for what you use, scale automatically, and never think about infrastructure.

Sentinel's Architecture

Sentinel is built on four core capabilities:

1. Data Collection

Data Connectors ingest logs from hundreds of sources — Azure AD, Microsoft 365, firewalls, Linux servers, cloud services. The key is starting with the most important sources:

• Azure AD / Entra ID sign-in logs — — detects compromised accounts
• Microsoft 365 audit logs — — reveals insider threats and data exfiltration
• Windows Security Events — — the foundation of endpoint detection
• Firewall/proxy logs — — network traffic and C2 communication

2. Analytics Rules

Scheduled and NRT (Near Real-Time) rules run KQL queries against log data. Sentinel ships with hundreds of built-in rules, but the best SOCs write custom rules tailored to their environment.

3. Incident Management

When a rule triggers, an incident is created with associated alerts, entities, and a timeline. Analysts can investigate incidents directly in Sentinel using the investigation graph.

4. Automation (SOAR)

Playbooks built on Logic Apps automate response — from enriching alerts with threat intelligence to blocking IP addresses and isolating machines. Automation is the difference between a SOC that drowns and one that scales.

How to Build a SOC with Sentinel

Start Small

Don't connect every log source on day one. Start with identity (Entra ID) and email (M365), then expand based on risk and maturity.

Invest in KQL

Kusto Query Language is Sentinel's foundation. Teams that master KQL build better detections, hunt more effectively, and understand their data more deeply.

Measure What Matters

• Mean Time to Detect (MTTD) — — how quickly do you spot attacks?
• Mean Time to Respond (MTTR) — — how quickly do you handle them?
• False positive rate — — how much noise do your rules generate?

Automate the Repetitive

Every time an analyst performs the same manual task three times, it should become a playbook.

Common Pitfalls

• Too many log sources too early — — costs explode before you have capacity to use the data
• Only built-in rules — — they're generic and create noise in your environment
• No response process — — Sentinel finds threats, but without processes it stops there
• Lack of expertise — — the tool is powerful but requires people who know how to use it

ForSec designs and operates cloud-native SOC solutions with Microsoft Sentinel. We help with everything from architecture and log strategy to rule development and 24/7 monitoring. Get in touch for a no-obligation assessment.