title: Monitoring Python 3.6 Functions on AWS Lambda

slug: monitor-python-3-6-example-code-aws-lambda-rollbar

meta: Monitor your Python 3.6 application code on Amazon Web Services (AWS) Lambda functions using Rollbar.

category: post

date: 2018-04-20

modified: 2018-04-20

newsletter: False

headerimage: /img/180420-monitor-aws-lambda/header.jpg

headeralt: Python, AWS Lambda and Rollbar logos are copyright their respective owners.

[Amazon Web Services (AWS) Lambda](/aws-lambda.html) is a usage-based

execution environment that can run Python 3.6 code. If you have never

previously used AWS Lambda then you can read

[How to Create Your First Python 3.6 AWS Lambda Function](/blog/aws-lambda-python-3-6.html).

However, this tutorial will give you every step to follow even if you

are completely new to AWS.

In this post we are going to monitor Python code that is running on AWS

Lambda by using a hosted [monitoring](/monitoring.html) service,

[Rollbar](/rollbar.html).

A local [development environment](/development-environments.html) is not

required to follow this tutorial. All the work will happen in a web

browser through the [AWS Console](https://console.aws.amazon.com/console/).

The example code can be copy and pasted from this blog post or you

can access it on GitHub under the

[Full Stack Python blog-post-examples](https://github.com/fullstackpython/blog-code-examples)

repository within the

[monitor-aws-lambda-python-3-6 directory](https://github.com/fullstackpython/blog-code-examples/monitor-aws-lambda-python-3-6).

[Sign into your existing AWS account](https://aws.amazon.com/console)

or sign up for a [new account](https://aws.amazon.com/). AWS Lambda

comes with a free tier so you can test code and execute basic

applications without cost.

<img src="/img/180420-monitor-aws-lambda/aws-amazon-com.jpg" width="100%" class="shot rnd outl" alt="AWS Lambda landing page.">

AWS has a boatload of services so use the search box to enter

"lambda" and select "Lambda" when it appears to get to the appropriate

starting page.

<img src="/img/180420-monitor-aws-lambda/search-for-lambda.jpg" width="100%" class="shot rnd outl" alt="Search for lambda in the dashboard text box.">

Click "Create a Lambda function" and the "Select Blueprint" page should

appear.

<img src="/img/180420-monitor-aws-lambda/select-blueprint.jpg" width="100%" class="shot rnd outl" alt="The Select Blueprint Lambda screen.">

Select "Blank Function". The "Configure triggers" page should appear next.

A trigger is how the Lambda function typically knows

when to execute based on an event from another AWS service like

[Cloudwatch](https://aws.amazon.com/cloudwatch/) or

[API Gateway](https://aws.amazon.com/api-gateway/).

<img src="/img/180420-monitor-aws-lambda/configure-triggers.jpg" width="100%" class="shot rnd outl" alt="Screen for configuring the AWS Lambda trigger.">

You do not need to configure a trigger to move to the next screen so

we will not configure a trigger for this function. We can manually

kick off the Lambda to test it when we are done with configuring it. Leave

the trigger icon blank and click "Next" to continue.

<img src="/img/180420-monitor-aws-lambda/blank-lambda.jpg" width="100%" class="shot rnd outl" alt="Blank AWS Lambda function.">

Ok, finally we arrive at the "Configure function" screen where we can write

our code.

Enter a name for the Lambda function, such as "python_3_6_lambda_test",

as well as a description. A description is optional but it is useful

when you have a dozens or hundreds of different Lambda functions and

need to keep them straight. In the Runtime drop-down, select Python 3.6 for

the programming language.

<img src="/img/170429-aws-lambda-python-3-6/python-3-6-lambda.jpg" width="100%" class="technical-diagram img-rounded bordered" alt="Enter a name, description and use Python 3.6 for the Lambda.">

Beneath the Runtime drop-down there is a large text box for code,

prepopulated with a `lambda_handler` function definition. The

"Code entry type" drop-down can also be changed to allow uploading a ZIP

file or inputing a file from an S3 bucket. For our simple first

Lambda function we will stick to the "Edit code inline" option. Copy or type

in the following code, replacing what is already in the text box. This

code is also available on [this open source GitHub repository](https://github.com/fullstackpython/blog-code-examples/blob/master/aws-lambda-python-3-6/).

import os

def lambda_handler(event, context):

what_to_print = os.environ.get("what_to_print")

how_many_times = int(os.environ.get("how_many_times"))

# make sure what_to_print and how_many_times values exist

if what_to_print and how_many_times > 0:

for i in range(0, how_many_times):

# formatted string literals are new in Python 3.6

print(f"what_to_print: {what_to_print}.")

return what_to_print

return None

The code above contains a required `lambda_handler` function, which is

AWS Lambda's defined hook so it knows where to begin execution. Think of

`lambda_handler` as a `main` function, like the

`if __name__ == "__main__":` conditional line commonly used in Python files

to ensure a block of code is executed when a script is run from the

command line.

The Python code expects two environment variables that are read by the

`os` module with the `environ.get` function. With the `what_to_print` and

`how_many_times` variables set by the environment variables, our code then

then prints a message zero or more times, based on the amount defined in

the `how_many_times` variable. If a message is printed at least once then

the function returns the `what_to_print` string, if nothing is printed

then `None` is returned.

Below the code input text box on this function configuration screen there

is a section to set environment variable key-value pairs.

Enter the keys named `what_to_print` and `how_many_times` then enter their

values. Use a string message for `what_to_print`'s value and an integer

whole number above 0 for `how_many_times`. Our Python code's error handling

is not very robust so a value other than a number in the `how_many_times`

variable will cause the script to throw an error when it is executed due

to the forced casting of `how_many_times` via the `int()` function.

<img src="/img/170429-aws-lambda-python-3-6/environment-variables.jpg" width="100%" class="technical-diagram img-rounded bordered" alt="Section to set environment variables for the Lambda function.">

The Python 3.6 code and the environment variables are now in place. We

just need to handle a few more AWS-specific settings before we can test the

Lambda function.

Scroll past the environment variables to the

"Lambda function handler and role" section, which contains a few more

required function configuration items.

Keep the default handler set to `lambda_function.lambda_handler`. Select

"Create a new Role from template(s)" from the drop-down then for the

"Role name" field enter "dynamodb_access". Under "Policy templates"

select the "Simple Microservice permissions".

The "Simple Microservice permissions" allows our Lambda to access

[AWS DynamoDB](https://aws.amazon.com/dynamodb/). We will not use DynamoDB in

this tutorial but the service is commonly used either as permanent or

temporary storage for Lambda functions.

<img src="/img/170429-aws-lambda-python-3-6/lambda-handler-and-role.jpg" width="100%" class="technical-diagram img-rounded bordered" alt="For the final configuration, keep the default handler, create a new role from a template for Simple Microservice permissions and save it with a unique name.">

Our code and configuration is in place so click the "Next" button

at the bottom right corner of the page.

<img src="/img/170429-aws-lambda-python-3-6/review-lambda.jpg" width="100%" class="technical-diagram img-rounded bordered" alt="Review Lambda configuration.">

The review screen shows us our configuration settings to make sure we

selected the appropriate values for our new Lambda function. Scroll down

press "Create function".

<img src="/img/170429-aws-lambda-python-3-6/create-function.jpg" width="100%" class="technical-diagram img-rounded bordered" alt="Click the create function button to continue.">

Success message should appear on the next page below the "Test" button.

<img src="/img/170429-aws-lambda-python-3-6/test.jpg" width="100%" class="technical-diagram img-rounded bordered" alt="Test button on the execution screen.">

Click the "Test" button to execute the Lambda. Lambda will prompt us for

some data to simulate an event that would kick off our function. Select

the "Hello World" sample event template, which contains some keys but our

Lambda will not use that in its execution. Click the "Save and test" button

at the bottom of the modal.

<img src="/img/170429-aws-lambda-python-3-6/sample-event-template.jpg" width="100%" class="technical-diagram img-rounded bordered" alt="Sample event template for Lambda execution.">

Scroll down to the "Execution result" section where we can see our output.

<img src="/img/170429-aws-lambda-python-3-6/execution-results.jpg" width="100%" class="technical-diagram img-rounded bordered" alt="Results from executing our new Lambda function.">

The log output shows us the return value of our function, which in this

execution was the string message from `what_to_print`. We can also see

our print function produced output five times as expected based on the

amount set in the `how_many_times` environment variable.

We just wrote and executed a Python 3.6 function on AWS Lambda then

captured the exception message into our Rollbar logs. Now you can

continue building out your Python code knowing that when something

goes wrong you will have full visibility on what happened.

Check out the [AWS Lambda section](/aws-lambda.html) for

more tutorials by other developers.

Further questions? Contact me on Twitter

or [@mattmakai](https://twitter.com/mattmakai). I am also on GitHub with

the username [mattmakai](https://github.com/mattmakai).

Something wrong with this post? Fork

[this page's source on GitHub](https://github.com/mattmakai/fullstackpython.com/blob/master/content/posts/180420-monitor-aws-lambda-python-3-6.markdown)

and submit a pull request.