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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
711
A Python lambda function behaves like a normal function in regard to arguments. Therefore, a lambda parameter can be initialized with a default value: the parameter n takes the outer n as a default value. The Python lambda function could have been written as lambda x=n: print(x) and have the same result.
Just like a normal function, a Lambda function can have multiple arguments with one expression. In Python, lambda expressions (or lambda forms) are utilized to construct anonymous functions. To do so, you will use the lambda keyword (just as you use def to define normal functions).
We can declare a lambda function and call it as an anonymous function, without assigning it to a variable. Above, lambda x: x*x defines an anonymous function and call it once by passing arguments in the parenthesis (lambda x: x*x)(5) .
Defaults in Python Lambda ExpressionIn Python, and in other languages like C++, we can specify default arguments.
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']
You can use the queryStringParameters on event object.
request_data = event['queryStringParameters']
startStop = request_data['startStop']
vertical = request_data['vertical']
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