Use Azure Function trigger to avoid costly Logic Apps polling

Logic Apps polling for files or messages can be rather costly if the requirements are such that the file or message must be taken care of within shortly.

Polling every 10th second (one Logic App) for one month will generate 6 * 60 * 24 * 30 => 259200 actions.

The monthly cost for this will be 250000 * 0,000675 + 9200 * 0,000338 = 171,8596 Euro Actual prices 2017-08-11, SeeĀ Logic App Pricing

Suppose we have at least 10 scenarios like this and the yearly cost will be approximately 172 * 10 * 12 = 20640 Euro

One way to eliminate (almost) the polling cost is to let Azure Function triggers do the job. The cost for that is almost nothing (less than one Euro), only cost for storage account and execution of function when the function is triggered.

So how do we do this?

In this example we want to take action when a new file is stored in a Dropbox folder.

Create a new Azure function and choose External File as input trigger. Select Dropbox as the API Connection.

Logic Apps Polling, Azure Function Bindings

Bindings:
Logic Apps Polling, Azure Function Bindings

Create a message to the Logic App containing data about the actual file. The function will then call the Logic App. Function:
Logic Apps Polling, Azure Function Code

The Logic App is triggered by the call from the Azure Function and the file can be processed.
Logic Apps Polling, Logic Apps Designer

Logic Apps Polling, Logic Apps Codeview

Other blog posts that addresses the Logic Apps polling case:
Be careful of the Logic App Consumption Prizing model
Save costs by scheduling Logic Apps

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