Durable Functions

Durable Functions let you write stateful workflows in Azure Functions. You can chain, fan out, and wait for external events in a serverless environment.

Key Capabilities

• Orchestrate complex workflows with code
• Chain and fan-out/fan-in function calls
• Wait for human interaction or external events
• Track state and progress automatically

When to Use

Use Durable Functions when you need to:

• Implement long-running workflows
• Coordinate multiple Azure Functions
• Wait for external events or approvals

Example: Orchestrator Function

C#

[FunctionName("E1_HelloSequence")]
public static async Task<List<string>> Run(
    [OrchestrationTrigger] IDurableOrchestrationContext context)
{
    var outputs = new List<string>();
    outputs.Add(await context.CallActivityAsync<string>("E1_SayHello", "Tokyo"));
    outputs.Add(await context.CallActivityAsync<string>("E1_SayHello", "Seattle"));
    outputs.Add(await context.CallActivityAsync<string>("E1_SayHello", "London"));
    return outputs;
}

Java

public class HelloSequenceOrchestrator {
    @FunctionName("HelloSequence")
    public List<String> run(
        @OrchestrationTrigger(name = "context") DurableOrchestrationContext context) {
        List<String> outputs = new ArrayList<>();
        outputs.add(context.callActivity("SayHello", "Tokyo", String.class));
        outputs.add(context.callActivity("SayHello", "Seattle", String.class));
        outputs.add(context.callActivity("SayHello", "London", String.class));
        return outputs;
    }
}

Python

def main(context):
    outputs = []
    outputs.append(yield context.call_activity('SayHello', 'Tokyo'))
    outputs.append(yield context.call_activity('SayHello', 'Seattle'))
    outputs.append(yield context.call_activity('SayHello', 'London'))
    return outputs

Resources

• Durable Functions documentation