Whisking Functions with Promises using OpenWhisk

Over the past few weeks I have been learning and enhancing my skills around the new buzz word “serverless” and trying to understand what this buzz is all about.  As an ardent open-source developer, I was looking for a platform where I can develop and deploy the serverless functions, which is when I stumbled upon Apache OpenWhisk.

In this blog I will demonstrate how to build a simple nodejs function that can do reverse geocoding using Google Maps API, and how to deploy the functions on to Apache OpenWhisk.

The context is to show building an Apache OpenWhisk JavaScript action, which involves a callback.  As most of us are familiar with Google Maps API (which has lots of callbacks), it provides a good example for this blog.

The source code of this blog is available on my github repository.

Since I am a newbie to nodejs development, I did make several mistakes around configuration, function, definition, and invoking the function.  This blog will explain what I did wrong, and what I did to make the function work as expected.

With the context set, lets start writing the function (first of the wrong way ;)) that does the reverse geocoding for us using the Google Maps API:

For the sake of brevity and sticking to the context of this blog, I am skipping details of source repo and related npm scripts. For the rest of this blog we only need know:

  • build is npm run build
  • action deploy is npm run deploy
  • action invoke is npm run dev

After we build npm run build, deploy  npm run deploy  the function, we invoke the action via npm run dev  always returning the result as:

{status: status,location: Unknown}

I did not have any clue on why that did not work. 🙁
However, with a bit of research and consulting the OpenWhisk actions document I found that I was not properly handling the callback function of the Google Map client “reverseGeocode” method. I then decided to wrap the callback within Promise and return a Promise as a response of the OpenWhisk nodejs Action.

Following the OpenWhisk actions documentation, I tried updating the code as:

Invoking the action post doing npm run build took me from bad to worse, with action hung and no response. 🙁

Polling the OpenWhisk logs via wsk activation poll showed the following lines:

Activation: ‘location-finder’ (750f66bd750d426d8f66bd750d026d2a)[
“2018-02-23T05:27:06.453Z stderr: There was an issue while collecting your logs. Data might be missing.”
]

With further analysis and debug, I found that I need to make the Google Map client promise aware.

I did the further and final modification to the function as:

Two important changes:

  • Line#11 – where I created the Google Maps client to promise aware.
  • I modified the node function to return the promise from the location function via asPromise() method.

Doing a rebuild, deploy, and run returned the expected response:

{
“location”: “New Row, London WC2N 4LH, UK”,
“status”: “OK”
}

In this example we saw how Promise can be configured on the Google Map client. If you are using similar functions from the other API, you need to check on how to hook on to the API call that can give you a handle to a Promise.

In summary, the crucial learnings here are about how to return a Promise the correct way from an Apache OpenWhisk JavaScript action. When invoking the OpenWhisk action, it should return the response which will be part of the future (Promise), and should not exit the function immediately after the main function ends.

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