How to do it...

1. Create the project from the following template:

$ sls create --template-url https://github.com/danteinc/js-cloud-native-cookbook/tree/master/ch2/db-first-cognito --path cncb-db-first-cognito

2. Navigate to the cncb-db-first-cognito directory with cd cncb-db-first-cognito.
3. Review the file named serverless.yml with the following content:

service: cncb-db-first-cognito

provider:
  name: aws
  runtime: nodejs8.10
  ...

functions:
  trigger:
    handler: handler.trigger
    events:
      - stream:
          type: kinesis
          arn:
            Fn::GetAtt: [ CognitoStream, Arn ]
          ...
    environment:
      STREAM_NAME: ${cf:cncb-event-stream-${opt:stage}.streamName}

resources:
  Resources:
    CognitoStream:
      Type: AWS::Kinesis::Stream
      Properties:
          ShardCount: 1

    IdentityPool:
      Type: AWS::Cognito::IdentityPool
      Properties:
        CognitoStreams:
          StreamName:
            Ref: CognitoStream
    ...

  Outputs:
    identityPoolId:
      Value: 
        Ref: IdentityPool
    identityPoolName:
      Value: 
        Fn::GetAtt: [ IdentityPool, Name ]

4. Review the file named handler.js with the following content:

module.exports.trigger = (event, context, cb) => {
  _(event.Records)
    .flatMap(recordToSync)
    .map(toEvent)
    .flatMap(publish)
    .collect().toCallback(cb);
};

const recordToSync = r => {
  const data = JSON.parse(Buffer.from(r.kinesis.data, 'base64'));
  return _(data.kinesisSyncRecords.map(sync => ({
    record: r,
    data: data,
    sync: sync,
    thing: JSON.parse(sync.value)
  })));
}

const toEvent = uow => ({
  id: uuid.v1(),
  type: `thing-created`,
  timestamp: uow.sync.lastModifiedDate,
  partitionKey: uow.thing.id,
  tags: {
    region: uow.record.awsRegion,
    identityPoolId: uow.data.identityPoolId,
    datasetName: uow.data.datasetName
  },
  thing: {
      identityId: uow.data.identityId, // the end user
      ...uow.thing,
  },
  raw: uow.sync
});

...

5. Install the dependencies with npm install.
6. Run the tests with npm test -- -s $MY_STAGE.
   
7. Review the contents generated in the .serverless directory.
8. Deploy the stack:

$ npm run dp:lcl -- -s $MY_STAGE

> cncb-db-first-cognito@1.0.0 dp:lcl <path-to-your-workspace>/cncb-db-first-cognito
> sls deploy -v -r us-east-1 "-s" "john"

Serverless: Packaging service...
...
Serverless: Stack update finished...
...
functions:
  trigger: cncb-db-first-cognito-john-trigger

Stack Outputs
identityPoolName: IdentityPool_P6awUWzjQH0y
identityPoolId: us-east-1:e51ba12c-75c2-4548-868d-2d023eb9398b
...

9. Review the stack, function, and identity pool in the AWS Console.
10. Update the file named ./index.html with the  identityPoolId from the previous output.

11. Open the file named ./index.html in a browser, enter a name and description, and press Save and then Synchronize, as shown in the following screenshot:

12. Take a look at the logs:

$ sls logs -f trigger -r us-east-1 -s $MY_STAGE

START ...
2018-04-19 00:50:15 ... {"id":"2714e290-438d-11e8-b3de-2bf7e0b964a2","type":"thing-created","timestamp":1524113413268,"partitionKey":"fd398c3b-8199-fd26-8c3c-156bb7ae8feb","tags":{"region":"us-east-1","identityPoolId":"us-east-1:e51ba12c-75c2-4548-868d-2d023eb9398b","datasetName":"things"},"thing":{"identityId":"us-east-1:28a2c685-2822-472e-b42a-f7bd1f02545a","id":"fd398c3b-8199-fd26-8c3c-156bb7ae8feb","name":"thing six","description":"the sixth thing"},"raw":{"key":"thing","value":"{\"id\":\"fd398c3b-8199-fd26-8c3c-156bb7ae8feb\",\"name\":\"thing six\",\"description\":\"the sixth thing\"}","syncCount":1,"lastModifiedDate":1524113413268,"deviceLastModifiedDate":1524113410528,"op":"replace"}}
2018-04-19 00:50:15 ... params: {"StreamName":"john-cncb-event-stream-s1","PartitionKey":"fd398c3b-8199-fd26-8c3c-156bb7ae8feb","Data":{"type":"Buffer","data":[...]}}
END ...
REPORT ... Duration: 217.22 ms    Billed Duration: 300 ms ... Max Memory Used: 40 MB    

13. Remove the stack once you have finished with npm run rm:lcl -- -s $MY_STAGE