In today post we will talk about how we can replicate content in multiple storage accounts of Azure. If you remember the last post that I had, this one is related to it and describes the replication process. First of all Why we need to do something like this? There are cases when we have a system that is distributed on multiple data centers and we want to be able to have the specific content in all locations around the globe. We don’t want a user from China to requests binary content from Europe if the system is deployed in China also. We could use CDNs but CDNs don’t have support for Shared Access Signature (SAS) Beside this, if we have a lot of clients that will requests the same blob content than we will have a problem. A blob can handle maximum 500 requests and the bandwidth that is available per blob is around 60MB. This mean that if we have 100 clients, that wants to download the content with 1MB each than... will have a small problem. When we talk about replication don’t imagine that replication needs to be done on different datacenters. The content can be replicated in the same datacenters on different blobs under the same storage account or using different storage accounts. Below, we can see a diagram that present a replication schema that is: On two storage accounts in the main datacenters On four other datacenters (one storage account per data centers) The secret around replication action is ‘StartCopyFromBlobAsync’. This method allow us to trigger a copy action from a blob to another blob. In this way we can easily copy all the content of a blob (including properties, metadata and payload) to another blob without having manually to manage each step. Once the action is triggered, you will need to check the async operation status and make sure that the copy action finished with success. await destinationBlob.StartCopyFromBlobAsync(new Uri(sourceBlobUri)); The status that is returned by can be: CopyStatus.Aborded – the copy action was aborted CopyStatus.Failed – an error occurred CopyStatus.Pending – copy is still in progress CopyStatus.Success – copy was finished We don’t have any control at how long the copy action will take. Because of this we need to wait the action to finish and check the status code. As input uri, we can even use a secure blob storage that has a SAS token. public class BlobReplication { public async Task ReplicateBlobAsync(string blobSasUri, CancellationToken cancellationToken = default(CancellationToken)) { List destBlobs = new List(); try { var sasUri = new Uri(blobSasUri); var blobClient = new CloudBlobClient(sasUri); ICloudBlob sourceBlob = blobClient.GetBlobReferenceFromServer(sasUri); var startCopyTasks = new List>(); foreach (var destConnectionString in configuration.ReplicationStorageAccounts.Select(c => c.ConnectionString)) { var destStorageAccount = CloudStorageAccount.Parse(destConnectionString); if (destStorageAccount.BlobEndpoint.ToString() != storageAccount.BlobEndpoint.ToString()) { var task = StartReplicationAsync(sourceBlob, blobSasUri, destStorageAccount, cancellationToken); startCopyTasks.Add(task); } } await Task.WhenAll(startCopyTasks); destBlobs = startCopyTasks.Select(t => t.Result).ToList(); await WaitForBlobCopy(destBlobs, cancellationToken); } catch (OperationCanceledException) { foreach (var dest in destBlobs) { try { var destBlob = dest.Container.GetBlobReferenceFromServer(dest.Name); if (destBlob.CopyState.Status == CopyStatus.Pending) { destBlob.AbortCopy(destBlob.CopyState.CopyId); } } catch (Exception) { ... } } throw; } } private async Task StartReplicationAsync(ICloudBlob sourceBlob, string sourceBlobSasUri, CloudStorageAccount destStorageAccount, CancellationToken cancellationToken = default (CancellationToken)) { string containerName = sourceBlob.Container.Name; CloudBlobContainer destContainer = await destStorageAccount.GetBlobContainerAsync(containerName); ICloudBlob destBlob; if (sourceBlob.Properties.BlobType == BlobType.BlockBlob) { destBlob = destContainer.GetBlockBlobReference(sourceBlob.Name); } else { destBlob = destContainer.GetPageBlobReference(sourceBlob.Name); } await destBlob.StartCopyFromBlobAsync(new Uri(sourceBlobSasUri), cancellationToken); return destBlob; } private async Task WaitForBlobCopy(List blobs, CancellationToken cancellationToken = default(CancellationToken)) { Dictionary failedAttempts = blobs.ToDictionary(k => k.Uri.ToString(), v => 0); bool pendingCopy = true; while (pendingCopy) { cancellationToken.ThrowIfCancellationRequested(); pendingCopy = false; foreach (var dest in blobs) { pendingCopy |= await IsCopyInProgress(dest, failedAttempts, cancellationToken); } if (pendingCopy) { await Task.Delay(configuration.ReplicationStatusPollingInterval, cancellationToken); } } } private async Task IsCopyInProgress(ICloudBlob dest, IDictionary failedAttempts, CancellationToken cancellationToken = default(CancellationToken)) { bool pendingCopy = false; var destBlob = await dest.Container.GetBlobReferenceFromServerAsync(dest.Name, cancellationToken); switch (destBlob.CopyState.Status) { case CopyStatus.Aborted: case CopyStatus.Failed: int numberOfFailes; if (failedAttempts.TryGetValue(destBlob.Uri.ToString(), out numberOfFailes) && numberOfFailes