Azure Storage Blobs

Overview

Update Blobs in Azure Storage

This article describes how to update the data of a block blob in Azure Storage. Azure Blob Storage is a service for storing large amounts of unstructured data, such as text or binary data. Anything that can be stored as text or binary data can be stored in Blob Storage.

Note: In Azure Blob Storage, a blob is immutable by design. Updating a blob actually means overwriting the entire blob with new content. There is no direct "update" operation that modifies a portion of a blob.

You can update blob content using the Azure portal, Azure CLI, Azure PowerShell, or client SDKs.

Methods for Updating Blobs

1. Overwriting a Blob using the Azure Portal

The simplest way to update a blob is through the Azure portal. This involves uploading a new file with the same name as the existing blob, which effectively overwrites it.

  1. Navigate to your Storage Account in the Azure portal.
  2. Select Containers under Data storage.
  3. Open the container that contains the blob you want to update.
  4. Locate the blob, select its ellipsis (...) menu, and choose Upload new version.
  5. Select the new file from your local machine.

2. Overwriting a Blob using Azure CLI

You can use the Azure CLI to overwrite a blob. The following command demonstrates how to upload a local file, overwriting an existing blob if it has the same name:

az storage blob upload --account-name  \
    --container-name  \
    --name  \
    --file  \
    --auth-mode login \
    --overwrite

Replace the placeholders with your specific values. The --overwrite flag is crucial for this operation.

3. Overwriting a Blob using Azure PowerShell

Azure PowerShell provides cmdlets to manage Azure resources, including blob storage.

Set-AzStorageBlobContent -Container  `
    -Blob  `
    -File  `
    -Force `
    -Context (Get-AzStorageAccount -ResourceGroupName  -Name ).Context

The -Force parameter ensures that the blob is overwritten if it already exists.

4. Overwriting a Blob using Client SDKs

You can programmatically update blobs using the Azure Storage SDKs for various languages like Python, .NET, Java, and Node.js. The general approach involves creating a blob client and then using an upload or overwrite method.

Here's an example using the Azure Blob Storage SDK for Python:


from azure.storage.blob import BlobServiceClient, BlobClient, ContainerClient

connect_str = ""
container_name = ""
blob_name = ""
local_file_path = ""

try:
    blob_service_client = BlobServiceClient.from_connection_string(connect_str)
    blob_client = blob_service_client.get_blob_client(container=container_name, blob=blob_name)

    with open(local_file_path, "rb") as data:
        blob_client.upload_blob(data, overwrite=True)
    print(f"Blob '{blob_name}' updated successfully.")

except Exception as e:
    print(f"An error occurred: {e}")

In this Python example, overwrite=True is the key parameter to update the blob.

Considerations When Updating Blobs

  • Immutability: Remember that each "update" is a complete replacement of the blob's content.
  • Cost: Each overwrite operation incurs transaction costs.
  • Performance: For very large blobs, overwriting can take time. Consider chunked uploads or other strategies for large data.
  • Lease Management: If your blob has an active lease, you may need to manage the lease during the update process, depending on your requirements.
  • Access Tiers: Updating a blob does not typically change its access tier unless explicitly managed.

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