AWS Serverless Lambda Scheduled Events to Store Tweets in Couchbase

Arun GuptaJanuary 19th, 2017Last Updated: January 19th, 2017

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This blog has explained a few Serverless concepts with code samples:

This particular blog entry will show how to use AWS Lambda to store tweets of a tweeter in Couchbase. Here are the high level components:

The key concepts are:

Lambda Function deployed using Serverless Application Model
Triggered every 3 hours using Scheduled Events
Uses Twitter4J API to query new tweets since the last fetch
Use Couchbase Java SDK API to store JSON documents in the Couchbase Server

Complete sample code for this blog is available at github.com/arun-gupta/twitter-n1ql.

Serverless Application Model

Serverless Application Model, or SAM, defines simplified syntax for expressing serverless resources. SAM extends AWS CloudFormation to add support for API Gateway, AWS Lambda and Amazon DynamoDB. Read more details in Microservice using AWS Serverless Application Model and Couchbase.

For our application, SAM template is available at github.com/arun-gupta/twitter-n1ql/blob/master/template-example.yml and shown below:

AWSTemplateFormatVersion : '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: Twitter Feed Analysis using Couchbase/N1QL
Resources:
  TrumpFeed:
    Type: AWS::Serverless::Function
    Properties:
      Handler: org.sample.twitter.TwitterRequestHandler
      Runtime: java8
      CodeUri: s3://arungupta.me/twitter-feed-1.0-SNAPSHOT.jar
      Timeout: 30
      MemorySize: 1024
      Environment:
        Variables:
          COUCHBASE_HOST: <value>
          COUCHBASE_BUCKET_PASSWORD: <value>
      Role: arn:aws:iam::598307997273:role/microserviceRole
      Events:
        Timer:
          Type: Schedule
          Properties:
            Schedule: rate(3 hours)

What do we see here?

Function is packaged and available in a S3 bucket
Handler class is org.sample.twittter.TwitterRequestHandler and is at github.com/arun-gupta/twitter-n1ql/blob/master/twitter-feed/src/main/java/org/sample/twitter/TwitterRequestHandler.java. It looks like:

public class TwitterRequestHandler implements RequestHandler<Request, String> {
 
    @Override
    public String handleRequest(Request request, Context context) {
        if (request.getName() == null)
            request.setName("realDonaldTrump");
        
        int tweets = new TwitterFeed().readFeed(request.getName());
        
        return "Updated " + tweets + " tweets for " + request.getName() + "!";
    }
    
}

By default, this class reads the twitter handle of Donald Trump. More fun on that coming in a subsequent blog.
COUCHBASE_HOST and COUCHBASE_BUCKET_PASSWORD are environment variables that provide EC2 host where Couchbase database is running and the password of the bucket.
Function can be triggered by different events. In our case, this is triggered every three hours. More details about the expression used here are at Schedule Expressions Using Rate or Cron.

Fetching Tweets using Twitter4J

Tweets are read using Twitter4J API. It is an unofficial Twitter API that provides a Java abstraction over Twitter REST API. Here is a simple example:

Twitter twitter = getTwitter();
Paging paging = new Paging(page, count, sinceId);
List<Status> list = twitter.getUserTimeline(user, paging);

Twitter4J Docs and Javadocs are pretty comprehensive.

Twitter API allows to read only last 200 tweets. Lambda function is invoked every 3 hours. The tweet frequency of @realDonaldTrump is not 200 every 3 hours, at least yet. If it does reach that dangerous level then we can adjust the rate to trigger Lambda function more frequently.

JSON representation of each tweet is stored in Couchbase server using Couchbase Java SDK. AWS Lambda supports Node, Python and C#. And so you can use Couchbase Node SDK, Couchbase Python SDK or Couchbase .NET SDK to write these functions as well.

Twitter4J API allows to fetch tweets since the id of a particular tweet. This allows to ensure that duplicate tweets are not fetched. This requires us to sort all tweets in a particular order and then pick the id of the most recent tweet. This was solved using the simple N1QL query:

SELECT id FROM twitter ORDER BY id DESC LIMIT 1

The syntax is very SQL-like. More on this in a subsequent blog.

Store Tweets in Couchbase

The final item is to store the retrieved tweets in Couchbase.

Value of COUCHABSE_HOST environment variable is used to connect to the Couchbase instance. The value of COUCHBASE_BUCKET_PASSWORDenvironment variable is to connect to the secure bucket where all JSON documents are stored. Its very critical that the bucket be password protected and not directly specified in the source code. More on this in a subsequent blog.

The JSON document is upserted (insert or update) in Couchbase using the Couchbase Java API: