About

This example shows how to create a scheduled lambda function that will look for new HackerNews stories containing certain keywords and send links to a slack channel. It will also send notifications when a chosen user posts a comment/story or when someone comments on their comment/story.

How it works

Here we are using the official HackerNews API which is described here. We will also make use of the mantil KV store to persist data about items we have already processed.

When the function is invoked, it first fetches the ID of the last processed item from the KV store and the ID of the newest item from the HN API. For each item, it then checks if it contains certain keywords. In this case, we are interested in stories that contain discussions about lambdas in go or general serverless topics. When such an item is found, we traverse its parents until we find the associated story and send the link to a slack channel via the provided webhook.

For user activity alerts, we check if each item is:

• a story posted by the user
• a comment on a story posted by the user
• a comment posted by the user
• a reply to a comment posted by the user

For example, here we check if the item is a comment on the user's story.

Prerequisites

This example is created with Mantil. To download Mantil CLI on Mac or Linux use Homebrew

brew tap mantil-io/mantil
brew install mantil

or check direct download links.

To deploy this application you will need an AWS account.

Installation

To locally create a new project from this example run:

mantil new app --from hn-alerts
cd app

Configuration

Before deploying your application you will need to create a Slack webhook and add it as an environment variable for your function which will be used to post notifications to your Slack channel.

Detailed instructions on how to create a webhook can be found here.

Once your webhook is created you need to add URL to the config/environment.yml file as env variable for your function.

project:
  stages: 
    - name: development
      functions:
      - name: alerts
        cron: "* * * * ? *"
        env:
          SLACK_WEBHOOK: # add your slack webhook here

Here you can also choose a user to receive notifications for by setting the HN_USER variable:

project:
  stages: 
    - name: development
      functions:
      - name: alerts
        cron: "* * * * ? *"
        env:
          SLACK_WEBHOOK: # add your slack webhook here
          HN_USER: # add a HackerNews username here

You can also change the function's schedule by changing the cron field. For example, this config will result in the function being invoked every 5 minutes:

project:
  stages: 
    - name: development
      functions:
      - name: alerts
        cron: "*/5 * * * ? *"
        env:
          SLACK_WEBHOOK: # add your slack webhook here
          HN_USER: # add a HackerNews username here

For more information refer to the docs.

Deploying the application

Note: If this is the first time you are using Mantil you will need to install Mantil Node on your AWS account. For detailed instructions please follow the setup guide

mantil aws install

Then you can proceed with application deployment.

mantil deploy

This command will create a new stage for your project with the default name development and deploy it to your node.

The alerts function will be invoked every minute by default. You can also manually invoke it using manil invoke alerts.

Cleanup

To remove the created stage from your AWS account destroy it with:

mantil stage destroy development

Final thoughts

With this example you learned how to create a scheduled lambda function. It also uses persistent key/value storage that you can learn more about in todo example.

If you have any questions or comments on this template or would just like to share your view on Mantil contact us at [email protected].