Durable Functions for workflows in Azure - Step-by-Step Execution

Process Flow - Durable Functions for workflows

Start Workflow Trigger

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Orchestrator Function

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Call Activity Function 1

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Wait for Activity 1 Completion

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Call Activity Function 2

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Wait for Activity 2 Completion

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Complete Workflow

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Return Result to Caller

The workflow starts with a trigger, then the orchestrator calls activity functions one by one, waits for each to finish, and finally completes the workflow returning the result.

Execution Sample

Azure

async function orchestrator(context) {
  const result1 = await context.callActivity('Activity1');
  const result2 = await context.callActivity('Activity2');
  return result1 + result2;
}

This orchestrator function calls two activities in order, waits for each to finish, then returns the combined result.

Process Table

Step	Action	Function Called	Waiting	Result	Next Step
1	Start workflow trigger	Orchestrator	No	N/A	Call Activity1
2	Call Activity1	Activity1	Yes	N/A	Wait for Activity1 completion
3	Activity1 completes	Activity1	No	5	Call Activity2
4	Call Activity2	Activity2	Yes	N/A	Wait for Activity2 completion
5	Activity2 completes	Activity2	No	10	Complete workflow
6	Return combined result	Orchestrator	No	15	End

💡 Workflow ends after all activities complete and orchestrator returns combined result.

Status Tracker

Variable	Start	After Step 3	After Step 5	Final
result1	undefined	5	5	5
result2	undefined	undefined	10	10
combinedResult	undefined	undefined	undefined	15

Key Moments - 3 Insights

Why does the orchestrator wait after calling an activity function?

The orchestrator pauses to wait for the activity function to complete and return a result before moving on, as shown in steps 2 and 4 in the execution_table.

Can the orchestrator call multiple activities at the same time?

Yes, but in this example it calls them one after another to keep the workflow simple and ordered, as seen in the sequential calls in the execution_table.

What happens if an activity function fails?

The orchestrator can retry or handle errors, but this example assumes success to keep the flow clear, focusing on waiting and result collection.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of result1 after step 3?

A 5

B undefined

C 10

D 15

💡 Hint

Check the 'Result' column at step 3 where Activity1 completes.

At which step does the orchestrator call Activity2?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Function Called' column to find when Activity2 is called.

If Activity1 returned 7 instead of 5, what would be the final combinedResult?

A 12

B 17

C 15

D 10

💡 Hint

combinedResult is the sum of result1 and result2 as shown in variable_tracker.

Concept Snapshot

Durable Functions orchestrate workflows by calling activity functions in order.
The orchestrator waits for each activity to finish before continuing.
Results from activities can be combined and returned.
This enables reliable, stateful workflows in the cloud.

Full Transcript

Durable Functions let you build workflows that run in the cloud. A workflow starts with a trigger that calls an orchestrator function. The orchestrator calls activity functions one by one. It waits for each activity to finish before moving on. Each activity returns a result. The orchestrator can combine these results and return a final output. This process ensures the workflow is reliable and can handle long-running tasks. The execution table shows each step: starting the workflow, calling activities, waiting, and completing. Variables like result1 and result2 track activity outputs. Beginners often wonder why the orchestrator waits; it does so to keep the workflow ordered and consistent. They also ask about parallel calls and error handling, which are possible but not shown here. The visual quiz tests understanding of variable values and step order. This summary helps beginners see how Durable Functions manage workflows step-by-step.