How to pass parameters to an AWS Lambda Function using Python

Question

I have written an AWS Lambda function in Python that filters through instances and turns them on or off depending on how they are tagged. This will show you a working function, and the set-up needed to get it working. If you have questions on anything post it in the comments.

Here is my Lambda Function as of now:

import boto3
def lambda_handler(event, context):
    startStop = event['startStop']
    vertical = event['vertical']
    isRunning = ''

    if(startStop == 'start'):
        isRunning = 'stopped'
    elif (startStop == 'stop'):
        isRunning = 'running'

    ec2 = boto3.resource('ec2')
    filters = [
        {
            'Name': 'instance-state-name', 
            'Values': [isRunning] 
        },
        {
            'Name': 'tag:Vertical',
            'Values': [vertical]
        }
    ]

    instances = ec2.instances.filter(Filters=filters)

    runningInstances = [instance.id for instance in instances]

    if len(runningInstances) > 0:
        if(startStop == 'start'):
            shuttingDown = ec2.instances.filter(InstanceIds=runningInstances).start()
        elif (startStop == 'stop'):
            shuttingDown = ec2.instances.filter(InstanceIds=runningInstances).stop()

For reference, here is my mapping template:

{
    "startStop":"$input.params('startStop')",
    "vertical":"$input.params('vertical')"
}

And this is how I am passing in the parameters within the URL:

https://awslambdaapiurl.../prod/-params?startStop=start&vertical=TEST

I ended up figuring out the answer to my original question, so I have posted the working code as a resource for anyone to look at. — Doug Andres
– Doug Andres, Commented Jul 19, 2017 at 20:31
Can you just paste what you did as an answer and mark this as answered. — Abhigna Nagaraja
– Abhigna Nagaraja, Commented Jul 21, 2017 at 17:50
Sure, should I just delete the post and then re-post it as an answer? @AbhignaNagaraja — Doug Andres
– Doug Andres, Commented Jul 21, 2017 at 18:31
@DougAndres It's not necessary to repost. Just rollback the changes in the question as it was at the beginning (stackoverflow.com/revisions/45198321/1), and add what you did as an answer for this question. Then, mark it as answered and that's it! :-) — JonDoe297
– JonDoe297, Commented Jul 12, 2018 at 22:45

cellepo · Accepted Answer · 2019-12-28 21:21:15Z

5

Pass in parameter values in a mapping template:

{
    "startStop":"$input.params('startStop')",
    "vertical":"$input.params('vertical')"
}

Read parameter values via event Object:

    startStop = event['startStop']
    vertical = event['vertical']

answered Dec 28, 2019 at 21:21

cellepo

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Comments

Chandra Shekhar Goka · Accepted Answer · 2020-09-24 09:17:42Z

4

You can use the queryStringParameters on event object.

request_data = event['queryStringParameters']
startStop = request_data['startStop']
vertical = request_data['vertical']

answered Sep 24, 2020 at 9:17

Chandra Shekhar Goka

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Comments

Weston A. Greene · Accepted Answer · 2024-01-11 16:29:53Z

4

The Asker answered their question by editing their post, but for other newbies: When passing parameters via URL, the event parameter within the lambda_handler function is a dictionary where the URL parameters are within the queryStringParameters key:

Entering in your browser https://awslambdaapiurl/?startStop=start&vertical=TEST would be accessed by python within the lambda_handler function as:

event['queryStringParameters']['startStop']
event['queryStringParameters']['vertical']

answered Jan 11, 2024 at 16:29

Weston A. Greene

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1 Comment

Weston A. Greene Over a year ago

My answer is identical to stackoverflow.com/a/64043328/4420657, just more wordy. I am leaving my answer in addition since I feel the more verbose explanation was needed for my brain.

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