AWS Classroom notes – 12/08/2021

AWS Lambda functions

• Lambda function to stop ec2 instances

import json
import boto3

print('Loading function')


def lambda_handler(event, context):
    #print("Received event: " + json.dumps(event, indent=2))
    print(type(context))
    print(type(event))
    name = event['Key']
    value = event['Value']
    instance_ids = get_ec2_instance_id(key=name, value=value)
    stop_ec2(instance_ids)
    return instance_ids  # Echo back the first key value
    #raise Exception('Something went wrong')


def get_ec2_instance_id(key='Name', value='Web1'):
    ec2 = boto3.client('ec2')
    response = ec2.describe_instances(Filters = [
        {
            'Name': f'tag:{key}',
            'Values': [
                value,
            ]
        }])
    instance_ids = []
    for reservation in response['Reservations']:
        instance_ids.append(reservation['Instances'][0]['InstanceId'])
        print(reservation['Instances'][0]['InstanceId'])
    
    return instance_ids

def stop_ec2(instance_ids=[]):
    ec2 = boto3.client('ec2')
    try:
        if len(instance_ids) > 0:
            ec2.stop_instances(InstanceIds=instance_ids)
    except Exception as e:
        print(e)

• Lambda function which will be triggered has the following syntax is reffered as handler

def lambda_handler(event, context):
   pass

• The event is a dictionary which holds the values passed when triggering a lambda function
• context is a bootstrap.LambdaContext which has information about the current function and other details Refer Here

Invoation Types

• At a high level, lambda functions can be invoked using the following
  • A push: This is synchronous type of invocation where we make a request for the function to be invoked and wait for the function response.
  • An event: The asynchronous or event method for invoking functions is mainly used by other AWS services in the AWS ecosystem to prompt a lambda function as result of some action (example: when s3 object is uploaded invoke lambda function)
  • A Stream-based model

Event Sources

• The following are the ways in which we can invoke a lambda function
  • Via AWS Lambda Invoke API Refer Here
  • By using SDK Refer Here. Refer invoke and invoke async methods in Client of lambda
  • Event Sources