@middy/cloudwatch-metrics/index.js

import awsEmbeddedMetrics from 'aws-embedded-metrics'

const defaults = {}

const cloudwatchMetricsMiddleware = (opts = {}) => {
  const { namespace, dimensions } = { ...defaults, ...opts }
  const cloudwatchMetricsBefore = (request) => {
    const metrics = awsEmbeddedMetrics.createMetricsLogger()

    // If not set, defaults to aws-embedded-metrics
    if (namespace) {
      metrics.setNamespace(namespace)
    }

    // If not set, keeps defaults as defined here https://github.com/awslabs/aws-embedded-metrics-node/#configuration
    if (dimensions) {
      metrics.setDimensions(dimensions)
    }
    Object.assign(request.context, { metrics })
  }

  const cloudwatchMetricsAfter = async (request) => {
    await request.context.metrics.flush()
  }
  const cloudwatchMetricsOnError = async (request) => {
    try {
      await cloudwatchMetricsAfter(request)
    } catch (e) {}
  }

  return {
    before: cloudwatchMetricsBefore,
    after: cloudwatchMetricsAfter,
    onError: cloudwatchMetricsOnError
  }
}

export default cloudwatchMetricsMiddleware