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RBAC (Role Based Access Control) vs ACL (Access Control List)

🔹 RBAC (Role-Based Access Control)

  • Scope: At the Azure Resource level (Subscription → Resource Group → Storage Account → Container/File System).
  • Purpose: Controls management and broad access to resources.
  • Assigned via: Azure Active Directory (Azure AD).

  • Examples of RBAC roles:

  • Storage Blob Data Reader → can read blobs/files.

  • Storage Blob Data Contributor → can read/write/delete.
  • Storage Blob Data Owner → full control.

✅ Strengths:

  • Centralized (assign once at container level, applies to all).
  • Great for coarse-grained permissions.
  • Easy to manage across thousands of users.

❌ Limitations:

  • Not file/folder level → If you grant access to a file system, users see everything inside.
  • Cannot express “User A can only read /raw/sales/2025 but not /raw/hr.”

🔹 ACL (Access Control Lists)

  • Scope: At the data level (directory and file).
  • Purpose: Provides fine-grained, POSIX-like permissions within the hierarchical namespace.
  • Assigned via: Set on directories/files using ADLS Gen2 APIs, CLI, or Databricks/Spark.

  • ACLs have three types:

  • Read ® – view file contents, list directory.

  • Write (w) – modify contents.
  • Execute (x) – traverse directory / access child objects.

✅ Strengths:

  • Very granular (control at file/folder level).
  • Mimics traditional file systems (POSIX model).
  • Perfect for multi-team data lakes where each team should only see their zone.

❌ Limitations:

  • Can get complex to manage if you have thousands of folders.
  • Inheritance isn’t automatic unless you set default ACLs.

🔹 How RBAC and ACL Work Together in ADLS Gen2

👉 Think of it as two layers of security:

  1. RBAC decides: Can this user access this storage account / file system at all?
  2. ACLs decide: Within that file system, what directories and files can they actually read/write?

🔑 Rule: RBAC grants the door key, ACLs decide which rooms inside you can enter.

🔹 Example

Scenario:

  • Storage account: datalakeprod
  • File system: finance
  • Directory: /finance/reports/2025/

User: Alice (Finance Analyst)

  1. RBAC: Assign Storage Blob Data Reader at the finance file system level → Alice can access the file system.

  2. ACL:

  3. /finance/reports/2025/ → grant Alice read + execute

  4. /finance/raw/ → deny access

👉 Result: Alice can see and read reports from 2025, but she cannot even list or open files in the raw folder.

🔹 Summary

Feature RBAC ACL
Scope Azure resource level File system (directory/file)
Granularity Broad Fine-grained
Assigned via Azure AD POSIX-like model
Use case “Who can access this storage account or container?” “Within the container, what files/folders can they access?”
Best for Coarse access control Detailed data lake permissions

👉 In short:

  • RBAC = Door access to the building.
  • ACL = Which rooms and drawers inside you can open.