Uploading and Downloading Blobs

This document provides a comprehensive guide to uploading and downloading data to and from Azure Blob Storage using various methods and client libraries.

Overview

Azure Blob Storage is Microsoft's cloud object storage solution, optimized for storing massive amounts of unstructured data like text or binary data. Blobs can be accessed from anywhere in the world via HTTP or HTTPS. Blobs can be used to serve images or documents directly to a browser, store files for distributed access, stream video and audio, write to log files, store data for backup and restore, disaster recovery, and data archiving.

Methods for Uploading and Downloading

You can interact with Azure Blob Storage using several tools and SDKs. The most common methods are:

Azure Portal: A web-based interface for managing storage accounts and blobs.
Azure CLI: A command-line tool for managing Azure resources.
Azure PowerShell: A scripting environment for managing Azure resources.
Azure SDKs: Client libraries for various programming languages (e.g., .NET, Java, Python, Node.js, Go).
REST API: Direct HTTP/S requests for programmatic access.

Uploading Blobs

1. Using the Azure Portal

The Azure Portal offers a user-friendly way to upload individual files or folders.

Navigate to your storage account in the Azure Portal.
Select the container where you want to upload the blob.
Click the Upload button.
Choose files or a folder from your local machine.

2. Using Azure CLI

The Azure CLI provides efficient commands for uploading files. Replace <account-name>, <container-name>, and <local-path> with your specific values.


az storage blob upload \
    --account-name <account-name> \
    --container-name <container-name> \
    --name <blob-name> \
    --file <local-path>


Add-AzVhd -Destination "https://<account-name>.blob.core.windows.net/<container-name>/<blob-name>" -LocalFilePath "<local-path>"


az storage blob upload-append \
    --account-name <account-name> \
    --container-name <container-name> \
    --name <blob-name> \
    --file <local-path> \
    --offset <current-blob-size> \
    --block-size <block-size>


# PowerShell for append blobs is more complex and typically involves SDKs or multiple steps.
# Refer to official Azure documentation for detailed append blob operations in PowerShell.


az storage blob upload \
    --account-name <account-name> \
    --container-name <container-name> \
    --name <blob-name> \
    --file <local-path> \
    --type Page


# PowerShell for page blobs also involves specific cmdlets and is not a direct upload like block blobs.
# Use New-AzStorageBlob for page blob creation and Update-AzStorageBlob for page writes.

3. Using Azure SDKs (Python Example)

The Azure SDKs provide a programmatic way to upload blobs. Here's a Python example:


from azure.storage.blob import BlobServiceClient

connection_string = "YOUR_AZURE_STORAGE_CONNECTION_STRING"
container_name = "mycontainer"
local_file_name = "my_local_file.txt"
blob_name = "my_remote_blob_name.txt"

# Create the BlobServiceClient object
blob_service_client = BlobServiceClient.from_connection_string(connection_string)

# Get a client to interact with a specific blob
blob_client = blob_service_client.get_blob_client(container=container_name, blob=blob_name)

print(f"Uploading {local_file_name} to {blob_name}...")

with open(local_file_name, "rb") as data:
    blob_client.upload_blob(data)

print("Upload complete.")


const { BlobServiceClient } = require("@azure/storage-blob");

const connectionString = "YOUR_AZURE_STORAGE_CONNECTION_STRING";
const containerName = "mycontainer";
const blobName = "my_remote_blob_name.txt";
const localFilePath = "./my_local_file.txt"; // Path to your local file

async function uploadBlob() {
    const blobServiceClient = BlobServiceClient.from_connection_string(connectionString);
    const containerClient = blobServiceClient.getContainerClient(containerName);
    const blockBlobClient = containerClient.getBlockBlobClient(blobName);

    console.log(`Uploading ${localFilePath} to ${blobName}...`);

    const uploadResponse = await blockBlobClient.uploadFile(localFilePath, {
        onProgress: (progress) => console.log(`Progress: ${progress.loadedBytes} bytes`),
    });

    console.log("Upload complete.");
}

uploadBlob().catch((err) => {
    console.error("Error uploading blob:", err.message);
});


using Azure.Storage.Blobs;
using System;
using System.IO;

string connectionString = "YOUR_AZURE_STORAGE_CONNECTION_STRING";
string containerName = "mycontainer";
string blobName = "my_remote_blob_name.txt";
string localFilePath = "my_local_file.txt";

// Create the BlobServiceClient object
BlobServiceClient blobServiceClient = new BlobServiceClient(connectionString);

// Get a client to interact with a specific blob
BlobClient blobClient = blobServiceClient.GetBlobClient(blobName);

Console.WriteLine($"Uploading {localFilePath} to {blobName}...");

using (FileStream uploadFileStream = File.OpenRead(localFilePath))
{
    blobClient.UploadAsync(uploadFileStream, overwrite: true);
}

Console.WriteLine("Upload complete.");

Downloading Blobs

1. Using the Azure Portal

Similar to uploading, the portal allows easy download of blobs.

Navigate to your storage account and then to the container.
Select the blob you wish to download.
Click the Download button.

2. Using Azure CLI

The Azure CLI simplifies downloading blobs to your local machine.


az storage blob download \
    --account-name <account-name> \
    --container-name <container-name> \
    --name <blob-name> \
    --file <local-path-to-save>


Get-AzStorageBlobContent -Container <container-name> -Blob <blob-name> -Destination <local-path-to-save> -Context (Get-AzStorageAccount -ResourceGroupName <resource-group-name> -Name <account-name>).Context

3. Using Azure SDKs (Python Example)

Programmatically download blobs using the Azure SDKs. Here's a Python example:


from azure.storage.blob import BlobServiceClient

connection_string = "YOUR_AZURE_STORAGE_CONNECTION_STRING"
container_name = "mycontainer"
blob_name = "my_remote_blob_name.txt"
local_file_name = "my_downloaded_file.txt"

# Create the BlobServiceClient object
blob_service_client = BlobServiceClient.from_connection_string(connection_string)

# Get a client to interact with a specific blob
blob_client = blob_service_client.get_blob_client(container=container_name, blob=blob_name)

print(f"Downloading {blob_name} to {local_file_name}...")

with open(local_file_name, "wb") as download_file:
    download_stream = blob_client.download_blob()
    download_file.write(download_stream.readall())

print("Download complete.")


const { BlobServiceClient } = require("@azure/storage-blob");

const connectionString = "YOUR_AZURE_STORAGE_CONNECTION_STRING";
const containerName = "mycontainer";
const blobName = "my_remote_blob_name.txt";
const localFilePath = "./my_downloaded_file.txt"; // Path to save the downloaded file

async function downloadBlob() {
    const blobServiceClient = BlobServiceClient.from_connection_string(connectionString);
    const containerClient = blobServiceClient.getContainerClient(containerName);
    const blockBlobClient = containerClient.getBlockBlobClient(blobName);

    console.log(`Downloading ${blobName} to ${localFilePath}...`);

    await blockBlobClient.downloadToFile(localFilePath);

    console.log("Download complete.");
}

downloadBlob().catch((err) => {
    console.error("Error downloading blob:", err.message);
});


using Azure.Storage.Blobs;
using System;
using System.IO;

string connectionString = "YOUR_AZURE_STORAGE_CONNECTION_STRING";
string containerName = "mycontainer";
string blobName = "my_remote_blob_name.txt";
string localFilePath = "my_downloaded_file.txt";

// Create the BlobServiceClient object
BlobServiceClient blobServiceClient = new BlobServiceClient(connectionString);

// Get a client to interact with a specific blob
BlobClient blobClient = blobServiceClient.GetBlobClient(blobName);

Console.WriteLine($"Downloading {blobName} to {localFilePath}...");

// Download the blob to a local file
Response downloadResult = blobClient.Download();

using (FileStream downloadFileStream = File.OpenWrite(localFilePath))
{
    downloadFileStream.WriteAsync(downloadResult.Value.Content.ToArray());
}

Console.WriteLine("Download complete.");

Best Practices

Use appropriate blob types: Block blobs for general-purpose storage, append blobs for logging, and page blobs for VM disks.
Handle errors gracefully: Implement retry logic for transient network issues.
Security: Use Shared Access Signatures (SAS) or Azure AD for authenticated access. Avoid storing connection strings directly in client-side code.
Performance: For large files, consider using parallel uploads/downloads with the SDKs.

Important: Always replace placeholder values like YOUR_AZURE_STORAGE_CONNECTION_STRING, <account-name>, <container-name>, <blob-name>, and <local-path> with your actual Azure Storage details.

For more advanced scenarios, such as managing blob properties, setting access tiers, or working with snapshots, please refer to the official Azure Blob Storage documentation.

Azure Storage Docs

Uploading and Downloading Blobs

Overview

Methods for Uploading and Downloading

Uploading Blobs

1. Using the Azure Portal

2. Using Azure CLI

3. Using Azure SDKs (Python Example)

Downloading Blobs

1. Using the Azure Portal

2. Using Azure CLI

3. Using Azure SDKs (Python Example)

Best Practices