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How to Use the Blob Service from Node.js

This guide will show you how to perform common scenarios using the Windows Azure Blob service. The samples are written using the Node.js API. The scenarios covered include uploading, listing, downloading, and deleting blobs. For more information on blobs, see the Next Steps section.

Table of Contents

What is the Blob Service?

The Windows Azure Blob service is for storing large amounts of unstructured data that can be accessed from anywhere in the world via HTTP or HTTPS. A single blob can be hundreds of gigabytes in size, and a single storage account can contain up to 100TB of blobs. Common uses of Blobs include:

  • Serving images or documents directly to a browser
  • Storing files for distributed access
  • Streaming video and audio
  • Performing secure backup and disaster recovery
  • Storing data for analysis by an on-premises or Windows Azure-hosted service

You can use Blobs to expose data publicly to the world or privately for internal application storage.

Concepts

The Blob service contains the following components:

Blob1

  • URL format: Blobs are addressable using the following URL format:
    http://storageaccount.blob.core.windows.net/container/blob

    The following URL addresses one of the blobs in the diagram:
    http://sally.blob.core.windows.net/movies/MOV1.AVI

  • Storage Account: All access to Windows Azure Storage is done through a storage account. This is the highest level of the namespace for accessing blobs. An account can contain an unlimited number of containers, as long as their total size is under 100TB.

  • Container: A container provides a grouping of a set of blobs. All blobs must be in a container. An account can contain an unlimited number of containers. A container can store an unlimited number of blobs.

  • Blob: A file of any type and size. There are two types of blobs; block and page. Most files are block blobs. A single block blob can be up to 200GB in size. This tutorial uses block blobs. Page blobs, another blob type, can be up to 1TB in size, and are more efficient when ranges of bytes in a file are modified frequently.

Create a Windows Azure Storage Account

To use storage operations, you need a Windows Azure storage account. You can create a storage account by following these steps. (You can also create a storage account using the REST API.)

  1. Log into the Windows Azure Management Portal.

  2. At the bottom of the navigation pane, click +NEW.

    +new

  3. Click Storage Account, and then click Quick Create.

    Quick create dialog

  4. In URL, type a subdomain name to use in the URI for the storage account. The entry can contain from 3-24 lowercase letters and numbers. This value becomes the host name within the URI that is used to address Blob, Queue, or Table resources for the subscription.

  5. Choose a Region/Affinity Group in which to locate the storage. If you will be using storage from your Windows Azure application, select the same region where you will deploy your application.

  6. Click Create Storage Account.

Create a Node.js Application

Create a blank Node.js application. For instructions creating a Node.js application, see Create and deploy a Node.js application to a Windows Azure Web Site, Node.js Cloud Service (using Windows PowerShell), or Web Site with WebMatrix.

Configure Your Application to Access Storage

To use Windows Azure storage, you need to download and use the Node.js azure package, which includes a set of convenience libraries that communicate with the storage REST services.

Use Node Package Manager (NPM) to obtain the package

  1. Use a command-line interface such as PowerShell (Windows,) Terminal (Mac,) or Bash (Unix), navigate to the folder where you created your sample application.

  2. Type npm install azure in the command window, which should result in the following output:

    azure@0.6.0 ./node_modules/azure
├── easy-table@0.0.1
├── dateformat@1.0.2-1.2.3
├── xmlbuilder@0.3.1
├── eyes@0.1.7
├── colors@0.6.0-1
├── mime@1.2.5
├── log@1.3.0
├── commander@0.6.1
├── node-uuid@1.2.0
├── xml2js@0.1.14
├── async@0.1.22
├── tunnel@0.0.1
├── underscore@1.3.3
├── qs@0.5.0
├── underscore.string@2.2.0rc
├── sax@0.4.0
├── streamline@0.2.4
└── winston@0.6.1 (cycle@1.0.0, stack-trace@0.0.6, pkginfo@0.2.3, request@2.9.202)

  3. You can manually run the ls command to verify that a node_modules folder was created. Inside that folder find the azure package, which contains the libraries you need to access storage.

Import the package

Using Notepad or another text editor, add the following to the top the server.js file of the application where you intend to use storage:

var azure = require('azure');

Setup a Windows Azure Storage Connection

The azure module will read the environment variables AZURE_STORAGE_ACCOUNT and AZURE_STORAGE_ACCESS_KEY for information required to connect to your Windows Azure storage account. If these environment variables are not set, you must specify the account information when calling createBlobService.

For an example of setting the environment variables in a configuration file for a Windows Azure Cloud Service, see Node.js Cloud Service with Storage.

For an example of setting the environment variables in the management portal for a Windows Azure Web Site, see Node.js Web Application with Storage

How to: Create a Container

The BlobService object lets you work with containers and blobs. The following code creates a BlobService object. Add the following near the top of server.js:

var blobService = azure.createBlobService();

All blobs reside in a container. The call to createContainerIfNotExists on the BlobService object will return the specified container if it exists or create a new container with the specified name if it does not already exist. By default, the new container is private and requires the use of the access key to download blobs from this container.

blobService.createContainerIfNotExists(containerName, function(error){
    if(!error){
        // Container exists and is private
    }
});

If you want to make the files in the container public so that they can be accessed without requiring the access key, you can set the container’s access level to blob or container. Setting the access level to blob allows anonymous read access to blob content and metadata within this container, but not to container metadata such as listing all blobs within a container. Setting the access level to container allows anonymous read access to blob content and metadata as well as container metadata. The following example demonstrates setting the access level to blob:

blobService.createContainerIfNotExists(containerName
    , {publicAccessLevel : 'blob'}
    , function(error){
        if(!error){
            // Container exists and is public
        }
    });

Alternatively, you can modify the access level of a container by using setContainerAcl to specify the access level. The following example changes the access level to container:

blobService.setContainerAcl(containerName
    , 'container'
    , function(error){
        if(!error){
            // Container access level set to 'container'
        }
    });

How to: Upload a Blob into a Container

To upload data to a blob, use the createBlockBlobFromFile, createBlockBlobFromStream or createBlockBlobFromText methods. createBlockBlobFromFile uploads the contents of a file, while createBlockBlobFromStream uploads the contents of a stream. createBlockBlobFromText uploads the specified text value.

The following example uploads the contents of the test1.txt file into the 'test1' blob.

blobService.createBlockBlobFromFile(containerName
    , 'test1'
    , 'test1.txt'
    , function(error){
        if(!error){
            // File has been uploaded
        }
    });

How to: List the Blobs in a Container

To list the blobs in a container, use the listBlobs method with a for loop to display the name of each blob in the container. The following code outputs the name of each blob in a container to the console.

blobService.listBlobs(containerName, function(error, blobs){
    if(!error){
        for(var index in blobs){
            console.log(blobs[index].name);
        }
    }
});

How to: Download Blobs

To download data from a blob, use getBlobToFile, getBlobToStream, or getBlobToText. The following example demonstrates using getBlobToStream to download the contents of the test1 blob and store it to the output.txt file using a stream:

var fs=require('fs');
blobService.getBlobToStream(containerName
    , 'test1'
    , fs.createWriteStream('output.txt')
    , function(error){
        if(!error){
            // Wrote blob to stream
        }
    });

How to: Delete a Blob

Finally, to delete a blob, call deleteBlob. The following example deletes the blob named 'blob1'.

blobService.deleteBlob(containerName
    , 'blob1'
    , function(error){
        if(!error){
            // Blob has been deleted
        }
    });

Next Steps

Now that you’ve learned the basics of blob storage, follow these links to learn how to do more complex storage tasks.

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