async.md

Asynchronous actions

Returning asynchronous results

JavaScript functions that run asynchronously may need to return the activation result after the main function has returned. You can accomplish this by returning a Promise in your action.

1. Save the following content in a file called asyncAction.js.

function main(args) {
     return new Promise(function(resolve, reject) {
       setTimeout(function() {
         resolve({ done: true });
       }, 2000);
    })
 }

Notice that the main function returns a Promise, which indicates that the activation hasn't completed yet, but is expected to in the future.

The setTimeout() JavaScript function in this case waits for two seconds before calling the callback function. This represents the asynchronous code and goes inside the Promise's callback function.

The Promise's callback takes two arguments, resolve and reject, which are both functions. The call to resolve()fulfills the Promise and indicates that the activation has completed normally.

A call to reject() can be used to reject the Promise and signal that the activation has completed abnormally.

Testing asynchronous timeouts

1. Run the following commands to create the action and invoke it:

   ibmcloud fn action create asyncAction asyncAction.js

   ibmcloud fn action invoke --result asyncAction

   {
       "done": true
   }

   Notice that you performed a blocking invocation of an asynchronous action.

2. Fetch the last activation log to see how long the async activation took to complete:

   ibmcloud fn activation get --last
   

   {
      ...
      "start": 1574133220119,
      "end": 1574133222155,
      "duration": 2036,
      ...
   }

   Checking the duration field in the activation record, you can see that this activation took slightly over two seconds to complete.

{% hint style="info" %} Actions have a timeout parameter that enforces the maximum duration for an invocation. This value defaults to 60 seconds and can be changed to a maximum of 5 minutes. {% endhint %}

Let's look at what happens when an action invocation takes longer than the timeout.

1. Update the asyncAction timeout to 1000ms.

   ibmcloud fn action update asyncAction --timeout 1000

   ok: updated action asyncAction
   

2. Invoke the action and block on the result.

   ibmcloud fn action invoke asyncAction --result

   {
       "error": "The action exceeded its time limits of 1000 milliseconds."
   }

   The error message returned by the platform indicates the action didn't return a response within the user-specified timeout. If we change the timeout back to a value higher than the artificial delay in the function, it should work again.

3. Update the asyncAction timeout to 10000 ms.

   ibmcloud fn action update asyncAction --timeout 10000

   ok: updated action asyncAction
   

4. Invoke the action and block on the result.

   ibmcloud fn action invoke asyncAction --result

   {
       "done": true
   }

{% hint style="tip" %} Asynchronous actions are necessary for calling other APIs or cloud services. Don't forget about that timeout though! {% endhint %}

{% hint style="success" %} 🎉Bonus Exercise Try out this exercise Calling an external API from an Async action to test your knowledge! 🎉 {% endhint %}