Create custom metric

CloudWatch metric provides several metrics for Lambda functions such as:

  • The number of times the function is executed
  • The execution time of each time, error rates
  • Throttle count.

We will create a new metric that sums up the number of hits to DynamoDB that fail

  1. In the upload_docs function console, select Codetab and add the following line of code at the top of the function
client_cloudwatch = boto3.client('cloudwatch')
  • Add the following code to the except block of put_item to DynamoDB table before returning results
        client_cloudwatch.put_metric_data(
            Namespace='BooksList_Lambda',
            MetricData=[
                {
                    'MetricName': 'FailedConnectToDynamoDB',
                    'Dimensions': [
                        {
                            'Name': 'env',
                            'Value': 'staging'
                        },
                    ],
                    'Value': 1.0,
                    'Unit': 'Seconds'
                },
            ]
        )
  • The code helps you to create a new metric and push the data into it every time the connection to DynamoDB fails

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  1. Give the function permission to access and push data into metric - Select Configure tab and select Permissions on the left menu. - Select the execution role

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  1. Expand the policy, then click Edit

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  1. Add the following to the JSON tab and click Review policy
{
    "Sid": "VisualEditor0",
    "Effect": "Allow",
    "Action": "cloudwatch:PutMetricData",
    "Resourse": "*"
},

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  1. Click Save changes

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  1. Test POST API again with API Gateway
  2. Open the CloudWatch dashboard
  3. Click on Metrics in the left menu, then click All metrics
  4. In the Custom namespaces section appears the metric you created - UploadDocs_Lambda. Click it

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  1. Click env

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  1. Select staging, data display chart

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  1. You can choose to display parameters according to 1 day or 1 week time, line or number displayed at the top of the graph.

So we have created a custom metric. Next step we will use it to create a CloudWatch Alarm