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Aynchronous Functions

Asynchronous functions are queued up and run at some point in the future. Great for expensive or bulk operations.

Writing Async Functions

When writing functions, the only differences between an async function and a sync function are:

  1. There is no immediate response, output goes to the logs instead.
  2. The response when calling a function returns a JSON object containing the call_id.

Response:

{"call_id":"01BVJ2NZ1N07WGA00000000000"}

You can then use this call_id to retrieve information later.

Create a Function

Let's create a function and make it async:

user input

fn init --runtime go asyncfn
cd asyncfn

Now open `func.yaml` and add `type: async`, for example:

![user input](../images/userinput.png)
>```yaml
>name: asyncfn
>type: async
>version: 0.0.1
>runtime: go
>entrypoint: ./func

Now let's deploy it:

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fn deploy --local --app myapp

Now we've deployed it as an async function so when we call it, it will be queued up to run later.

And call the asyncfn function:

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fn call myapp /asyncfn

Now you'll get a response like:

{"call_id":"01BVJ5T7CA07WGE00000000000"}

Check Status and Get Logs

We can retrieve the function call status by checking the status endpoint in the API.

Using the CLI, try running the following, replacing CALL_ID with the call_id returned above.

user input

fn calls get myapp CALL_ID

You'll get something like the following:

ID: 01BVJ5T7CA07WGE00000000000
App: myapp
Route: /asyncfn
Created At: 2017-10-03T22:31:01.258Z
Started At: 2017-10-03T22:31:01.908Z
Completed At: 2017-10-03T22:31:02.615Z
Status: success

We can see that the Status is success which means the call finished properly. And you can see the time it started and completed.

But how do we check the logs to debug and ensure things ran properly? There's a log endpoint to allow you to check this and you can access it via the CLI with:

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fn logs get myapp CALL_ID

For this function, the logs will contain:

{"message":"Hello World"}

Wrapping Up

Congratulations! In this tutorial you learned how to create and setup an async function. It's not much different than a synchronous function as you learned, but it's a powerful difference for expensive, long running or batch operations.

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