Set Blob Immutability Policy

The Set Blob Immutability Policy operation sets the immutability policy on a blob. This operation doesn't update the blob's ETag. This API is available as of version 2020-06-12.

Request

The Set Blob Immutability Policy request may be constructed as follows. We recommend that you use HTTPS. Replace myaccount with the name of your storage account and myblob with the blob name for which the immutability policy is to be changed.

Method	Request URI	HTTP version
PUT	https://myaccount.blob.core.windows.net/mycontainer/myblob?comp=immutabilityPolicies	HTTP/1.1

URI parameters

You can specify the following additional parameters on the request URI:

Parameter	Description
snapshot	Optional. The snapshot parameter is an opaque DateTime value that, when it's present, specifies the blob snapshot to set a tier on. For more information about working with blob snapshots, see Create a snapshot of a blob
versionid	Optional for version 2019-12-12 and later. The versionid parameter is an opaque DateTime value that, when it's present, specifies the version of the blob to set a tier on.
timeout	Optional. The timeout parameter is expressed in seconds. For more information, see Set time-outs for Blob Storage operations.

Request headers

The required and optional request headers are described in the following table:

Request header	Description
Authorization	Required. Specifies the authorization scheme, storage account name, and signature. For more information, see Authorize requests to Azure Storage.
Date or x-ms-date	Required. Specifies the Coordinated Universal Time (UTC) for the request. For more information, see Authorize requests to Azure Storage.
x-ms-immutability-policy-until-date	Required. Indicates the retention until date to be set on the blob. This is the date until which the blob can be protected from being modified or deleted. For blob storage or general purpose v2 account, valid values are with RFC1123 format. Past times are not valid.
x-ms-immutability-policy-mode	Optional. If not specified, default value is Unlocked. Indicates the immutability policy mode to be set on the blob. For blob storage or general purpose v2 account, valid values are Unlocked/Locked. unlocked indicates the user may change the policy by increasing or decreasing the retention until date. locked indicates that these actions are prohibited.
x-ms-version	Required for all authorized requests. Specifies the version of the operation to use for this request. For more information, see Versioning for the Azure Storage services.
x-ms-client-request-id	Optional. Provides a client-generated, opaque value with a 1-kibibyte (KiB) character limit that's recorded in the logs when logging is configured. We highly recommend that you use this header to correlate client-side activities with requests that the server receives. For more information, see Monitor Azure Blob Storage.

This operation also supports the use of conditional headers to set the blob only if a specified condition is met. For more information, see Specify conditional headers for Blob Storage operations.

Request body

None.

Response

The response includes an HTTP status code and a set of response headers.

Status code

A successful operation returns status code 200 (OK).

For information about status codes, see Status and error codes.

Response headers

The response for this operation includes the headers below. The response may also include additional standard HTTP headers. All standard headers conform to the HTTP/1.1 protocol specification.

Response header	Description
x-ms-request-id	Uniquely identifies the request that was made and can be used to troubleshoot the request. For more information, see Troubleshoot API operations.
x-ms-version	Indicates the Blob Storage version that was used to execute the request. Returned for requests made against version 2009-09-19 and later.
x-ms-client-request-id	Can be used to troubleshoot requests and corresponding responses. The value of this header is equal to the value of the x-ms-client-request-id header if it's present in the request and the value contains no more than 1,024 visible ASCII characters. If the x-ms-client-request-id header isn't present in the request, it won't be present in the response.
x-ms-immutability-policy-until-date	Indicates the retention-until date to be set on the blob. This is the date until which the blob can be protected from being modified or deleted.
x-ms-immutability-policy-mode	Indicates the immutability policy mode that's set on the blob. Values are unlocked and locked. Theunlocked value indicates that the user may change the policy by increasing or decreasing the retention-until date, and locked indicates that these actions are prohibited.

Authorization

Authorization is required when calling any data access operation in Azure Storage. You can authorize the Set Blob Immutability Policy operation as described below.

Microsoft Entra ID

Azure Storage supports using Microsoft Entra ID to authorize requests to blob data. With Microsoft Entra ID, you can use Azure role-based access control (Azure RBAC) to grant permissions to a security principal. The security principal may be a user, group, application service principal, or Azure managed identity. The security principal is authenticated by Microsoft Entra ID to return an OAuth 2.0 token. The token can then be used to authorize a request against the Blob service.

To learn more about authorization using Microsoft Entra ID, see Authorize access to blobs using Microsoft Entra ID.

Permissions

Listed below are the RBAC action necessary for a Microsoft Entra user, group, or service principal to call the Set Blob Immutability Policy operation, and the least privileged built-in Azure RBAC role that includes this action:

• Azure RBAC action: Microsoft.Storage/storageAccounts/blobServices/containers/write
• Least privileged built-in role: Storage Blob Data Contributor

To learn more about assigning roles using Azure RBAC, see Assign an Azure role for access to blob data.

Shared access signatures (SAS)

A shared access signature (SAS) provides secure delegated access to resources in a storage account. With a SAS, you have granular control over how a client can access data. You can specify what resource the client may access, what permissions they have to those resources, and how long the SAS is valid.

The Set Blob Immutability Policy operation supports three types of shared access signatures: user delegation SAS, service SAS, and account SAS.

As a security best practice, we recommend that you use Microsoft Entra credentials rather than the storage account key, which can be more easily compromised. If your application design requires shared access signatures, use Microsoft Entra credentials to create a user delegation SAS, when possible.

When Shared Key access is disallowed for the storage account, a service SAS token or an account SAS token will not be permitted on a request to Blob Storage. To learn more, see Understand how disallowing Shared Key affects SAS tokens.

User delegation SAS

A user delegation SAS is secured with Microsoft Entra credentials and also by the permissions specified for the SAS.

Calling the Set Blob Immutability Policy operation using a SAS token delegated to a container or blob resource requires the Immutable storage (i) permission as part of the user delegation SAS token.

To learn more about the user delegation SAS, see Create a user delegation SAS.

Service SAS

A service SAS is secured with the storage account key. A service SAS delegates access to a resource in a single Azure Storage service, such as blob storage.

Calling the Set Blob Immutability Policy operation using a SAS token delegated to a container or blob resource requires the Immutable storage (i) permission as part of the service SAS token.

To learn more about the service SAS, see Create a service SAS.

Account SAS

An account SAS is secured with the storage account key. An account SAS delegates access to resources in one or more of the storage services. All of the operations available via a service or user delegation SAS are also available via an account SAS.

The following table indicates the signed resource type and signed permissions to specify when delegating access:

Operation	Signed service	Signed resource type	Signed permission
Set Blob Immutability Policy	Blob (b)	Object (o)	Immutable storage (i)

To learn more about the account SAS, see Create an account SAS.

Shared key

The Set Blob Immutability Policy operation supports Shared Key authorization. Authorizing with account keys is not recommended for most scenarios, as it's less secure.

Microsoft recommends disallowing Shared Key authorization for the storage account when possible. For more information, see Prevent authorization with Shared Key.

Remarks

Setting the blob's immutability policy on a blob storage or general purpose v2 account has the following restrictions:

• Setting an immutability policy on a snapshot or a version is allowed as of REST version 2020-06-12.
• When the immutability policy is in unlocked mode, users can update the retention until date. When the immutability policy is in locked mode, users can extend the retention until date only. Immutability policy mode can be changed from unlocked to locked, but not from locked to unlocked.
• When there's an immutability policy on a blob, and there's also a default immutability policy on container or account, the blob immutability policy takes precedent.
• For a blob-level immutability policy, PutBlockList/PutBlob/CopyBlob operations are allowed, because these operations generate a new version.
• When the immutability policy is in unlocked mode, users can delete the immutability policy by using the following API:

Method	Request URI	HTTP version
Delete	https://myaccount.blob.core.windows.net/mycontainer/myblob?comp=immutabilityPolicies	HTTP/1.1

Note

For more information, see Immutable storage.

Billing

Pricing requests can originate from clients that use Blob Storage APIs, either directly through the Blob Storage REST API, or from an Azure Storage client library. These requests accrue charges per transaction. The type of transaction affects how the account is charged. For example, read transactions accrue to a different billing category than write transactions. The following table shows the billing category for Set Blob Immutability Policy requests based on the storage account type:

Operation	Storage account type	Billing category
Set Blob Immutability Policy	Premium block blob Standard general-purpose v2 Standard general-purpose v1	Other operations

To learn about pricing for the specified billing category, see Azure Blob Storage Pricing.

See also

Authorize requests to Azure Storage
Status and error codes
Blob Storage error codes
Set time-outs for Blob Storage operations