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Details in Saga pattern - Azure Design Patterns | Microsoft Learn |
Problem
Data consistency is a major issue in distributed transaction scenarios.
Cross-service data consistency requires a cross-service transaction management strategy : transactions must be atomic, consistent, isolated and durable (ACID).
If a transaction (step) fails, the pattern will execute compensating transactions that counteract the preceding transactions.
Solution
Orchestration is a way to coordinate sagas where a centralized controller tells the saga participants waht local transactions to execute.
Orchestrator executes saga requests, stores and interprets the states of each task, and handles failure recovery with compensating transactions.
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Saga In Practice
Example of orchestration with Azure Function Apps and 2 different triggers : Call API from Web App (client application) or a change in a blob Storage.
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Example of Triggering with Azure Blob Storage
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public static class BlobTriggerStart
{
[FunctionName("BlobTriggerStart")]
public static async Task HttpBlobStart(
[BlobTrigger("photoscontainer/{name}", Connection = "StorageConnectionString")] CloudBlockBlob myCloudBlob, string name, ILogger log,
[DurableClient] IDurableOrchestrationClient starter)
{
try
{
log.LogInformation($"Started orchestration trigged by BLOB trigger. A blob item with name = '{name}'");
log.LogInformation($"BLOB Name {myCloudBlob.Name}");
// Function input comes from the request content.
if (myCloudBlob != null)
{
var newUploadedBlobItem = new CloudBlobItem
{
Name = myCloudBlob.Name,
BlobUrl = myCloudBlob.Uri.AbsoluteUri.ToString(),
Metadata = (Dictionary<string, string>)myCloudBlob.Metadata,
FileType = myCloudBlob.BlobType.ToString(),
Size = myCloudBlob.Name.Length.ToString(),
ETag = myCloudBlob.Properties.ETag.ToString()
};
var instanceId = await starter.StartNewAsync("AzureStorageOrchestrator", newUploadedBlobItem);
log.LogInformation($"Started orchestration with ID = '{instanceId}'.");
}
else
{
log.LogError($"The blob was trigged but myCloudBlob was empty");
}
}
catch (Exception ex)
{
//Errorhandling
log.LogError("Something went wrong. Error : " + ex.InnerException);
throw;
}
}
} |