Azure Blob Storage

1. What is Azure Blob Storage?

2. Core Concepts and Architecture

3. Blob Storage Tiers and Performance

• Access Tiers (Hot, Cool, Archive): Allows cost optimization by classifying blobs based on access frequency.
• Hot Tier for frequently accessed data.
• Cool Tier for infrequently accessed but available data with lower storage cost but higher access cost.
• Archive Tier for rarely accessed data with lowest storage cost but high latency and read cost on retrieval.

• Supports Standard (HDD) and Premium (SSD, Block blobs) performance tiers.

4. Pricing Model

5. Replication & Durability

6. Security & IAM

• Authentication: Supports Azure AD integration for Role-Based Access Control (RBAC) and Shared Access Signatures (SAS) for delegated access with fine-grained permissions.

• Encryption:
• Data encrypted at rest with Microsoft-managed keys or customer-managed keys (CMK) in Key Vault.
• TLS/SSL used for data in transit.

• Network Security: Supports Virtual Network (VNet) service endpoints, private endpoints (Azure Private Link), firewall, and IP restrictions.

• Access Control: Container and blob-level access policies; supports immutable blob storage for legal hold and retention.

7. Development & SDKs

Common ways to interact with Blob Storage:

• REST APIs over HTTP/HTTPS

• Azure SDKs (for .NET, Java, Python, JavaScript, Go, etc.)

• Azure CLI / PowerShell

• Azure Storage Explorer (GUI tool)

Sample: Uploading a block blob in C#

using Azure.Storage.Blobs;

string connectionString = "<your_storage_account_connection_string>";
string containerName = "mycontainer";
string blobName = "sample.txt";
string localFilePath = @"C:\temp\sample.txt";

// Create a BlobServiceClient
BlobServiceClient blobServiceClient = new BlobServiceClient(connectionString);

// Get the container client
BlobContainerClient containerClient = blobServiceClient.GetBlobContainerClient(containerName);

// Get the blob client
BlobClient blobClient = containerClient.GetBlobClient(blobName);

// Upload the file
await blobClient.UploadAsync(localFilePath, overwrite: true);

Sample: Download a blob

using Azure.Storage.Blobs;

string downloadFilePath = @"C:\temp\downloaded_sample.txt";
await blobClient.DownloadToAsync(downloadFilePath);

8. Blob Lifecycle Management & Features

• Blob Versioning: Automatically maintains versions of blobs upon modification or deletion.

• Soft Delete: Protects against accidental deletes by retaining deleted blobs for a retention period.

• Snapshots: Create point-in-time snapshots of blobs.

• Lifecycle Policies: Automate transitions between tiers (hot → cool → archive) and deletion of older blobs.

• Event Grid Integration: Blob storage can trigger events on blob creation/deletion to Azure Functions, Logic Apps, or Event Grid subscribers.

• Large File Uploads: Supports chunked (block) upload, resumable uploads, and parallel transfer.

9. Deployment and Configuration

• Create and manage via Azure Portal, Azure CLI, ARM/Bicep templates, PowerShell.

• Configure containers, permissions, Access Tiers, and lifecycle policies via portal or infrastructure-as-code.

• Key configuration in apps via connection strings or Managed Identity-based authentication.

• Access via URLs:
texthttps://<storage-account-name>.blob.core.windows.net/<container-name>/<blob-name>

10. Monitoring and Diagnostics

• Azure Monitor metrics for storage accounts (transactions, ingress/egress, availability).

• Diagnostic logs for read/write requests.

• Alerting on metrics thresholds.

• Use Azure Storage Explorer or third-party tools for deep inspection.

11. Best Practices

• Use SAS tokens with least privilege and short expiry to secure access.

• Use Managed Identities where possible for app access to storage.

• Prefer appropriate access tiers based on access patterns to save costs.

• Enable soft delete and versioning to protect data.

• Design for idempotent uploads and downloads to handle retries.

• Use lifecycle management to automate data retention and tier transitions.

• Optimize for large file performance using block blobs and parallel upload.

• Monitor storage performance and costs regularly.

Summary Table: Azure Blob Storage

FAQ

• Block blobs: Optimized for uploading large files as blocks; most common for file storage.

• Append blobs: Optimized for append operations, ideal for logging.

• Page blobs: Optimized for random read/write operations, commonly used for virtual hard disk (VHD) files for Azure virtual machines.

• Hot tier: For frequently accessed data; higher storage cost but low access cost.

• Cool tier: For infrequently accessed data; lower storage cost but higher access cost and retrieval latency.

• Archive tier: For rarely accessed data; lowest storage cost but requires hours to rehydrate data before access.

• Locally-redundant storage (LRS): Replicates data three times within a single datacenter.

• Zone-redundant storage (ZRS): Synchronously replicates data across availability zones within a region.

• Geo-redundant storage (GRS): Asynchronously replicates data to a paired secondary region for disaster recovery.

• Read-access geo-redundant storage (RA-GRS): Similar to GRS but allows read access to the secondary region.

• Authentication: Azure Active Directory (Azure AD) for RBAC and Shared Access Signatures (SAS) for delegated time-limited access.

• Encryption: Data is encrypted at rest with Microsoft-managed or customer-managed keys (via Azure Key Vault). Data in transit is secured via TLS/SSL.

• Network controls: Service endpoints, private endpoints (Azure Private Link), firewall rules, and IP restrictions.

• Access policies: Container- and blob-level permissions, immutable blob storage for retention and legal hold.

Intermediate and In-Depth Interview Questions and Answers

Advanced and Tricky Interview Questions and Answers