@mapbox/cloudfriend/lib/shortcuts/stream-lambda.js

Helper functions for assembling CloudFormation templates in JavaScript

'use strict';

const Lambda = require('./lambda');

/**
 * A Lambda function that runs in response to events in a DynamoDB or Kinesis
 * stream. Includes a Log Group, a Role, an Alarm on function errors, and an event
 * source mapping.
 *
 * @param {Object} options - Extends the options for [`Lambda`](#lambda) with the following additional attributes:
 * @param {String} options.EventSourceArn - See [AWS documentation](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-lambda-eventsourcemapping.html#cfn-lambda-eventsourcemapping-eventsourcearn).
 * @param {Number} [options.BatchSize=1] - See [AWS documentation](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-lambda-eventsourcemapping.html#cfn-lambda-eventsourcemapping-batchsize).
 * @param {Number} [options.MaximumBatchingWindowInSeconds=undefined] - See [AWS documentation](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-lambda-eventsourcemapping.html#cfn-lambda-eventsourcemapping-maximumbatchingwindowinseconds).
 * @param {Boolean} [options.Enabled=true] - See [AWS documentation](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-lambda-eventsourcemapping.html#cfn-lambda-eventsourcemapping-enabled).
 * @param {String} [options.StartingPosition='LATEST'] - See [AWS documentation](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-lambda-eventsourcemapping.html#cfn-lambda-eventsourcemapping-startingposition).
 * @param {Object} [options.FilterCriteria] - See [AWS documentation](https://docs.aws.amazon.com/lambda/latest/dg/invocation-eventfiltering.html).
 *
 * @example
 * const cf = require('@mapbox/cloudfriend');
 *
 * const myTemplate = { ... };
 *
 * const lambda = new cf.shortcuts.StreamLambda({
 *   LogicalName: 'MyLambda',
 *   Code: {
 *     S3Bucket: 'my-code-bucket',
 *     S3Key: 'path/to/code.zip'
 *   },
 *   EventSourceArn: cf.getAtt('MyStream', 'Arn'),
 * });
 *
 * // This lambda only gets invoked for 'INSERT' events for the DynamoDb event source
 * const lambdaWithFilterCriteria = new cf.shortcuts.StreamLambda({
 *  LogicalName: 'MyLambdaWithFilterCriteria',
 *  Code: {
 *    S3Bucket: 'my-code-bucket',
 *    S3Key: 'path/to/code.zip'
 *  },
 *  EventSourceArn: cf.getAtt('MyDynamoDbStream', 'Arn'),
 *  FilterCriteria: {
 *    Filters: [
 *      {
 *        Pattern: JSON.stringify({ eventName: ['INSERT'] }),
 *      }
 *    ]
 *  }
 * });
 *
 * module.exports = cf.merge(myTemplate, lambda, lambdaWithFilterCriteria);
 */
class StreamLambda extends Lambda {
  constructor(options) {
    if (!options) throw new Error('Options required');
    super(options);

    const {
      EventSourceArn,
      BatchSize = 1,
      MaximumBatchingWindowInSeconds,
      Enabled = true,
      StartingPosition = 'LATEST',
      FilterCriteria = undefined
    } = options;

    const required = [EventSourceArn];
    if (required.some((variable) => !variable))
      throw new Error('You must provide an EventSourceArn');

    this.Resources[`${this.LogicalName}EventSource`] = {
      Type: 'AWS::Lambda::EventSourceMapping',
      Condition: this.Condition,
      Properties: {
        BatchSize,
        MaximumBatchingWindowInSeconds,
        Enabled,
        EventSourceArn,
        FunctionName: { Ref: this.LogicalName },
        StartingPosition
      }
    };
    if (FilterCriteria) {
      if (Object.prototype.toString.call(FilterCriteria) !== '[object Object]'){
        throw new Error('`FilterCriteria` must be a JSON-like object');
      }
      if (!(FilterCriteria.Filters && Array.isArray(FilterCriteria.Filters))){
        throw new Error('`FilterCriteria` must contain property `Filter` of type array');
      }
      for (const filter of FilterCriteria.Filters){
        if (!filter.Pattern){
          throw new Error('An object in `FilterCriteria.Filter` was missing the required property `Pattern`');
        }
        try {
          JSON.parse(filter.Pattern);
        } catch (error) {
          throw new Error('An object in `FilterCriteria.Filter` contains a `Pattern` property that is not a JSON parseable string');
        }
      }
      this.Resources[`${this.LogicalName}EventSource`].Properties.FilterCriteria = FilterCriteria;
    }

    const generatedRoleRef = this.Resources[`${this.LogicalName}Role`];
    const streamStatement = {
      Effect: 'Allow',
      Action: [
        'dynamodb:GetRecords',
        'dynamodb:GetShardIterator',
        'dynamodb:DescribeStream',
        'dynamodb:ListStreams',
        'kinesis:GetRecords',
        'kinesis:GetShardIterator',
        'kinesis:DescribeStream',
        'kinesis:ListStreams'
      ],
      Resource: [
        EventSourceArn,
        { 'Fn::Sub': ['${arn}/*', { arn: EventSourceArn }] }
      ]
    };

    if (generatedRoleRef && generatedRoleRef.Properties.Policies) {
      generatedRoleRef.Properties.Policies[0].PolicyDocument.Statement.push(streamStatement);
    } else if (generatedRoleRef) {
      generatedRoleRef.Properties.Policies = [
        {
          PolicyName: 'StreamAccess',
          PolicyDocument: {
            Version: '2012-10-17',
            Statement: [streamStatement]
          }
        }
      ];
    }
  }
}

module.exports = StreamLambda;