My First Encounter with Azure Durable Function
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| pexels image from Arina Krasnikova |
Recently, I need to have an orchestrator in Azure Function App to monitor the status of a long-running job. Azure Duration Function comes in handy. In this blog, I am going to simplify the use case to focus solely on how Duration Function works.
User Case: A long-running job is executed and we need to monitor its status and log this status in a database.
Referencing the diagram above.
This is where the Duration Function is executed.
| (A) | fx is an Azure Function where the job is started. Following that, it makes a IDurableOrchestrationClient.StartNewAsync call to start a new Duration Function. We have the Job-Id and the expiration time in the context of this function. Essentially, Duration Function is an internal HTTP endpoint in Azure Function App. It looks like this[FunctionName("JobMonitoring")]
public async Task RunMonitor(
[OrchestrationTrigger] IDurableOrchestrationContext context)
{
...
}
|
| (B) | Here the JobMonitoring Durable Function is called. The following is the pseudocode.
[FunctionName("JobMonitoring")]
public async Task RunMonitor(
[OrchestrationTrigger] IDurableOrchestrationContext context)
{
var data = context.GetInput<ContextData>();
var expireTime = data.ExpireTime;
if (context.CurrentUtcDateTime < expireTime)
{
var status = await context.CallActivityAsync<string>(
"GetJobStatus", data.JobId);
if (status == "Processing")
{
var nextCheckpoint = context.CurrentUtcDateTime.AddMinutes(1);
await context.CreateTimer(nextCheckpoint, CancellationToken.None);
context.ContinueAsNew(data);
}
else
{
// store status in database
}
}
}
It checks if the All the information (context, function name, etc) around calling this function again in 1 minute is stored in Azure Blob Storage. The red circles show information stored and retrieved from Blob Storage. |
| (B') | After one minute, the Durable Function is executed again. |
| (BC) | Here the JobMonitoring Durable Function is called and the job status is completed. Job Status is stored in the database and the Durable Function ended. |
Essentially, the context of the Durable Function call is stored in Azure Blob Storage. During the time to invoke the function, a new runtime context object is created from the persisted blob entry.
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