Posts Tagged - CloudWatch

Not long ago I came across the problem that I wanted to know in detail how much of the allocated memory my individual lambda functions consumes.

Since memory consumption is not part of the standard Lambda metrics, I had to find an individual solution.

As each lambda execution logs the memory usage I thought about implementing a metric filter extracting this information to create a custom metric in AWS CloudWatch.

A sample metric filter was quickly found on the AWS forums (related thread).

You can test the metric filter by applying it to the log group of a lambda function like I did in the example below:

Now since verified the metric filter is actually working I only had to implement it in CloudFormation to be able to evaluate the memory consumption. It is important that a function name is defined so that the log group belonging to the Lambda function can also be created using the CloudFormation template.

You can find the template below:

Now you can find the memory consumption metric under StackName > LambdaFunctionName > Memory in AWS CloudWatch:

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Recently I had the following problem, a CloudWatch Alarm based on the Error-Metric of a critical Lambda Function occasionaly caused notifications.

The reason for the notifications was quickly found through a search in the lambda logs. The errors were caused by lambda timeouts. Since lambda timeouts are not critical in the utilised architecture I was looking for a way to ignore them in the CloudWatch Alarms.

The solution is called Metric Math.

Metric math enables you to query multiple CloudWatch metrics and use math expressions to create new time series based on these metrics.

Source: Using Metric Math by AWS

Herewith it is possible to create a new metric excluding the timeouts by subtracting timeouts from errors. By default there is no metric for timeouts within lambda functions. But this metric can be extracted with a simple Metric Filter applied to the loggroup of the respective lambda function:

Then a CloudWatch Alarm can be created with a mathematical expression:

In the CloudWatch console the result of the template looks like this:

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