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Azure Blob Upload

Upload JSON data to Azure Blob Storage from an Elsa 3.8.0 workflow.

The Elsa.Storage.AzureStorage extension provides one workflow activity, Upload blob. It serializes a non-null value as JSON and uploads the result to an existing Azure Blob Storage container as a block blob.

This is a server-side activity. The Elsa Server needs network access to Azure Storage and the authority represented by the container URI. Studio only edits the activity inputs; it does not upload the data from the browser.

Install and register the activity

Install the package in the application that executes workflows:

dotnet add package Elsa.Storage.AzureStorage --version 3.8.0

In 3.8.0, this package does not provide a UseAzureStorage() extension method. AzureStorageFeature registers the client factories, but does not register the activity itself. Configure both explicitly:

using Elsa.Extensions;
using Elsa.Storage.AzureStorage.Activities;
using Elsa.Storage.AzureStorage.Features;

builder.Services.AddElsa(elsa =>
{
    elsa.Use<AzureStorageFeature>();
    elsa.AddActivitiesFrom<UploadBlob>();
});

AddActivitiesFrom<UploadBlob>() scans the assembly containing UploadBlob for exported activity types. If you omit either registration, the activity cannot execute; if you omit the activity registration, it also will not appear in the server's activity descriptors for Studio.

Configure the activity

The activity has three inputs and no output:

Input
Type
Release behavior

Content

object

Serialized as JSON using the runtime type of the value. The value must be non-null and JSON-serializable.

ConnectionString

string

Despite its name, 3.8.0 parses this value as a Uri for an Azure container, not as a conventional DefaultEndpointsProtocol=... account connection string.

BlobName

string

Used as the blob path, with .json appended unconditionally.

For example, the following targets the workflow-files container using a SAS URI and creates orders/2026/00042.json:

The activity does not return the URI, ETag, or upload response. If a later step needs the location, keep the container URI and blob-name expression as workflow data or use a custom activity that exposes the result you need.

What is uploaded?

The activity is a JSON uploader, not a general binary-file uploader.

  • A string is uploaded as a JSON string value, including its quotes.

  • A byte[] is serialized according to System.Text.Json rather than copied as raw binary bytes.

  • Objects must be supported by the runtime JSON serializer.

  • The generated JSON is split into blocks and committed to Azure. The activity uses the uploader's 4 MiB approximate block-size and maximum concurrency of four defaults; it does not expose those settings as inputs.

Serialization is piped into the uploader instead of first constructing one complete JSON string. Pending blocks are still buffered in memory while they are staged, so set reasonable payload limits and account for concurrent workflow executions.

The implementation obtains a BlobContainerClient from the supplied URI and gets a BlockBlobClient for the resulting name. It does not create the container. Provision the container first and grant the SAS or other URI authority permission to stage and commit blocks.

Use it from Elsa Studio

After the server is configured and restarted, connect Studio to that server and search for Upload blob in the Storage category. Configure:

  1. Content with a literal or expression that evaluates to the JSON value.

  2. ConnectionString with the server-reachable container URI.

  3. BlobName with the path stem, without the .json suffix.

Studio has no Azure-specific connection picker or browser-side upload path for this activity in the 3.8.0 release. The inputs are sent to and evaluated by the server that runs the workflow. Installing the NuGet package in a Studio host alone does not make the activity available or executable.

Security and operations

  • Prefer a short-lived, least-privilege SAS URI or another host-controlled way to supply a scoped container URI. The ConnectionString input is still a raw string input in 3.8.0; the activity does not use Elsa's Connections API.

  • Do not commit account keys or long-lived SAS tokens in workflow definitions, examples, or logs. If the value is supplied through an expression, ensure the expression source is protected and that activity input logging is appropriate.

  • Treat BlobName as untrusted data when it is derived from external input; validate naming and length rules at the workflow boundary.

  • Use a unique name when previous blobs must be retained. Reusing a name targets the same blob path and can replace its committed block list.

  • Monitor activity failures and Azure Storage diagnostics. Authentication, invalid URI, missing-container, network, staging, and commit errors fault the activity; the source does not add a separate retry or dead-letter policy.

Troubleshooting

The activity is missing from Studio

Confirm that Elsa.Storage.AzureStorage is installed in the execution host, that Use<AzureStorageFeature>() and AddActivitiesFrom<UploadBlob>() run during Elsa configuration, and that Studio is connected to that server.

The URI is rejected

Use a valid container URI such as https://account.blob.core.windows.net/container?<sas-token>. A conventional storage-account connection-string value is not accepted by the 3.8.0 activity implementation despite the input label.

The upload fails with a storage resource error

Check that the container already exists and that the URI's credentials permit block staging and block-list commit. The activity does not provision the container.

The blob has an unexpected name or content

Remember that .json is appended to every BlobName, and that Content is serialized as JSON. This activity cannot be used to upload an arbitrary raw file stream without a custom activity or a different integration.

Release source

The behavior described here is based on the release/3.8.0 branches:

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