Create and manage blob leases with JavaScript
This article shows how to create and manage blob leases using the Azure Storage client library for JavaScript. You can use the client library to acquire, renew, release, and break blob leases.
Prerequisites
- The examples in this article assume you already have a project set up to work with the Azure Blob Storage client library for JavaScript. To learn about setting up your project, including package installation, importing modules, and creating an authorized client object to work with data resources, see Get started with Azure Blob Storage and JavaScript.
- The authorization mechanism must have permissions to work with a blob lease. To learn more, see the authorization guidance for the following REST API operation:
About blob leases
A lease creates and manages a lock on a blob for write and delete operations. The lock duration can be 15 to 60 seconds, or can be infinite. A lease on a blob provides exclusive write and delete access to the blob. To write to a blob with an active lease, a client must include the active lease ID with the write request.
To learn more about lease states and when you can perform a given action on a lease, see Lease states and actions.
All container operations are permitted on a container that includes blobs with an active lease, including Delete Container. Therefore, a container may be deleted even if blobs within it have active leases. Use the Lease Container operation to control rights to delete a container.
Lease operations are handled by the BlobLeaseClient class, which provides a client containing all lease operations for blobs and containers. To learn more about container leases using the client library, see Create and manage container leases with JavaScript.
Acquire a lease
When you acquire a blob lease, you obtain a lease ID that your code can use to operate on the blob. If the blob already has an active lease, you can only request a new lease by using the active lease ID. However, you can specify a new lease duration.
To acquire a lease, create an instance of the BlobLeaseClient class, and then use one of the following methods:
The following example acquires a 30-second lease for a blob:
async function acquireBlobLeaseAsync(blobClient) {
const leaseClient = blobClient.getBlobLeaseClient();
await leaseClient.acquireLease(30);
return leaseClient;
}
Renew a lease
You can renew a blob lease if the lease ID specified on the request matches the lease ID associated with the blob. The lease can be renewed even if it has expired, as long as the blob hasn't been modified or leased again since the expiration of that lease. When you renew a lease, the duration of the lease resets.
To renew a lease, use one of the following methods on a BlobLeaseClient instance:
The following example renews a lease for a blob:
async function renewBlobLeaseAsync(blobClient, leaseID) {
const leaseClient = blobClient.getBlobLeaseClient(leaseID);
await leaseClient.renewLease();
}
Release a lease
You can release a blob lease if the lease ID specified on the request matches the lease ID associated with the blob. Releasing a lease allows another client to acquire a lease for the blob immediately after the release is complete.
You can release a lease using one of the following methods on a JavaScript BlobLeaseClient instance:
The following example releases a lease on a blob:
async function releaseBlobLeaseAsync(blobClient, leaseID) {
const leaseClient = blobClient.getBlobLeaseClient(leaseID);
await leaseClient.releaseLease();
}
Break a lease
You can break a blob lease if the blob has an active lease. Any authorized request can break the lease; the request isn't required to specify a matching lease ID. A lease can't be renewed after it's broken, and breaking a lease prevents a new lease from being acquired until the original lease expires or is released.
You can break a lease using one of the following methods on a BlobLeaseClient instance:
The following example breaks a lease on a blob:
async function breakBlobLeaseAsync(blobClient) {
const leaseClient = blobClient.getBlobLeaseClient();
await leaseClient.breakLease();
}
Lease states and actions
The following diagram shows the five states of a lease, and the commands or events that cause lease state changes.
The following table lists the five lease states, gives a brief description of each, and lists the lease actions allowed in a given state. These lease actions cause state transitions, as shown in the diagram.
| Lease state | Description | Lease actions allowed |
|---|---|---|
| Available | The lease is unlocked and can be acquired. | acquire |
| Leased | The lease is locked. | acquire (same lease ID only), renew, change, release, and break |
| Expired | The lease duration has expired. | acquire, renew, release, and break |
| Breaking | The lease has been broken, but the lease will continue to be locked until the break period has expired. | release and break |
| Broken | The lease has been broken, and the break period has expired. | acquire, release, and break |
When a lease expires, the lease ID is maintained by the Blob service until the blob is modified or leased again. A client may attempt to renew or release the lease using the expired lease ID. If this operation is successful, the client knows that the blob hasn't been changed since the lease ID was last valid. If the request fails, the client knows that the blob was modified, or the blob was leased again since the lease was last active. The client must then acquire a new lease on the blob.
If a lease expires rather than being explicitly released, a client may need to wait up to one minute before a new lease can be acquired for the blob. However, the client can renew the lease with their lease ID immediately if the blob hasn't been modified.
A lease can't be granted for a blob snapshot, since snapshots are read-only. Requesting a lease against a snapshot results in status code 400 (Bad Request).
Resources
To learn more about managing blob leases using the Azure Blob Storage client library for JavaScript, see the following resources.
REST API operations
The Azure SDK for JavaScript contains libraries that build on top of the Azure REST API, allowing you to interact with REST API operations through familiar JavaScript paradigms. The client library methods for managing blob leases use the following REST API operation: