Azure Monitor & Log Analytics for Security

Microsoft Sentinel runs on a Log Analytics workspace. Defender for Cloud, Defender XDR hunting tables, Activity logs, and Diagnostic settings also flow there. The workspace strategy decides whether your security telemetry is complete, compliant, and affordable — or two of three.

This skill covers the security-side decisions in workspace design: tiering, retention, DCRs, RBAC, and cost.

When to use

Designing or refactoring the Log Analytics workspace(s) that back Sentinel and the broader security telemetry estate.

Do not use this skill for Sentinel detection authoring (sentinel-detection-engineering), App Insights instrumentation (appinsights-instrumentation), or non-security observability.

Log table tiers — pick per table

Microsoft has been re-naming/re-shaping these — verify current naming and pricing in your region before commit.

Approach

1. Workspace topology.

- Default: one Sentinel workspace per tenant for security signal — keeps correlation easy. - Regional / sovereign: separate workspaces where data residency or sovereignty requires. - Multi-workspace Sentinel: only when business reasons (M&A boundary, MSSP model) force it. Cross-workspace queries work but add complexity. - Don't split per-team; that fragments correlation.

1. Use Azure Monitor Agent (AMA) for everything new. The Microsoft Monitoring Agent

(MMA / Log Analytics agent) is retired. Migration paths via Defender for Cloud auto-provisioning and Sentinel solutions.

1. Define DCRs per data class.

- One DCR per data source family (Windows security events, Linux Syslog, custom logs). - Use transformKql to drop noisy columns or whole event IDs at ingest. A 30% pre-ingest reduction beats any post-ingest tuning. - Validate transformations against detection KQL — don't drop a column a Sentinel analytic relies on.

1. Tier per table.

- Analytics: SecurityEvent (filtered), SigninLogs, AuditLogs, DeviceLogonEvents (Defender XDR), Sentinel-driven detection sources. - Basic: AzureDiagnostics for chatty resources, NSG flow logs, web server access logs (where you need them only for incident search). - Auxiliary: long-retention compliance feeds (e.g., raw firewall logs for 12 months). Tier choice changes ingestion + retention costs significantly.

1. Retention and archive.

- Interactive retention: 90 days default — extend to align with detection lookback windows (often 180–730 days). - Archive (cold) for compliance and IR replay (12-year max for some scenarios). - Search jobs rehydrate archived data when needed.

1. Cost control.

- Commitment tier at the workspace (100 GB/day → 5,000 GB/day) cuts per-GB price ~15–30%. - Identify and cap top sources (DNS, NSG flow, Linux Syslog) — usually 80% of cost. - Daily cap as a guardrail (drops data above cap; alert on hit). - Review monthly: top tables, top resources, ingest trend.

1. Customer-managed keys (CMK) on the workspace if your data classification

requires. Plan for the dedicated cluster requirement and the operational complexity.

1. RBAC.

- Workspace-level: Log Analytics Reader, Log Analytics Contributor. - Table-level RBAC: scope analyst access to specific tables (e.g., HR mailbox audit visible only to insider-risk team). - Sentinel: separate Sentinel Reader / Responder / Contributor roles. - Avoid Owner on the workspace for SOC analysts.

1. Cross-workspace and cross-tenant.

- Sentinel workspace manager (preview/GA per region) for MSSP-style multi-tenant. - Cross-workspace queries via union for federated estates.

Guardrails

• Default 90-day retention is rarely enough for security investigations. APT

dwell-time medians exceed that. Plan 180–730 days for primary detection sources.

• Don't ingest everything in Analytics tier "to be safe." Cost spirals; add Basic

for "store and search-if-needed."

• Transformations are powerful and dangerous. A column drop today breaks a

detection tomorrow. Source-control DCRs and review changes.

• Daily cap as a cost control drops data — including security data. Pair with

alerting; never set a cap below high-water mark for security tables.

• Don't deploy MMA in 2025+. Use AMA. Existing MMA workloads need a migration plan.
• CMK on workspace requires dedicated cluster and ≥500 GB/day commitment. Big

operational and cost step.

• Multi-workspace Sentinel = harder hunting. Justify per business reason, not per

team preference.

• Archive recall is search jobs, not native query. SLA assumptions for IR change.
• Diagnostic settings are per resource; per-subscription policy is what scales.

Enforce via Azure Policy.

Common anti-patterns

• "Per-team workspace because each team wants 'their data'" — correlation breaks,

cost balloons.

• "Analytics tier for everything" — 5x cost vs Basic for tables you query

reactively.

• "NSG flow logs full-fidelity to Sentinel forever" — top cost driver. Sample,

transform, or Basic-tier.

• "30-day retention to keep cost down" — incidents discovered in week 6 have no

data.

• "Daily cap below normal volume" — silent data loss, missed detections.
• "DCRs hand-edited in the portal across 50 subs" — drift, no audit. Bicep + Azure

Policy.

• "Sentinel + Defender XDR in two separate workspaces" — cross-product hunting

pain. Unify.

• "Upgraded to dedicated cluster for CMK without volume justification" — cost

surprise.

Example prompts

• `Design the Log Analytics workspace strategy for a 100,000-employee multi-region

Sentinel deployment with sovereignty constraints in EU and APAC.`

• `Migrate 6,000 servers from MMA to AMA via Defender for Cloud auto-provisioning;

identify gaps in detection coverage during cutover.`

• `Author DCRs that drop high-noise columns from SecurityEvent and Syslog with 35%

expected ingest reduction.`

• `Tier plan: which tables go Analytics vs Basic vs Auxiliary for a Sentinel + DfC

workload, with retention.`

• `Cost optimization: identify top 10 cost drivers in our 12 TB/day workspace and

propose targeted reductions.`

• `Configure table-level RBAC so insider-risk analysts see EmailEvents but not

DeviceProcessEvents.`

• `Customer-managed key rollout for the security workspace — dedicated cluster, key

rotation, recovery runbook.`

• `Daily cap and ingestion alerting strategy that protects budget without dropping

detection-critical tables.`

Microsoft Learn

• Log Analytics workspace design: https://learn.microsoft.com/azure/azure-monitor/logs/workspace-design
• Table tiers (Analytics / Basic / Auxiliary): https://learn.microsoft.com/azure/azure-monitor/logs/data-platform-logs#table-plans
• Retention and archive: https://learn.microsoft.com/azure/azure-monitor/logs/data-retention-archive
• Azure Monitor Agent: https://learn.microsoft.com/azure/azure-monitor/agents/azure-monitor-agent-overview
• Data collection rules: https://learn.microsoft.com/azure/azure-monitor/essentials/data-collection-rule-overview
• Ingestion-time transformations: https://learn.microsoft.com/azure/azure-monitor/essentials/data-collection-transformations
• Commitment tiers and pricing: https://learn.microsoft.com/azure/azure-monitor/logs/cost-logs
• Workspace customer-managed keys: https://learn.microsoft.com/azure/azure-monitor/logs/customer-managed-keys
• Table-level RBAC: https://learn.microsoft.com/azure/azure-monitor/logs/manage-access#table-level-azure-rbac
• Sentinel + workspace requirements: https://learn.microsoft.com/azure/sentinel/prerequisites
• MMA retirement guidance: https://learn.microsoft.com/azure/azure-monitor/agents/azure-monitor-agent-migration