AWS Lambda Function Starter Template

AWS SAM local setup

• Install sam-cli - Details
• Install docker (required only to test functions locally)

Test application locally

Step1: Build

sam build -t sam/templates/template.yaml

Step2: Invoke

A lambda can be invoked locally using various event types. These events can be stored as json in a file. More details on generating events for local testing - Details

SQS

sam local invoke <lambda function resource name from template.yaml> -e sam/events/<filename>.json

example

sam local invoke SqsLambda -e sam/events/sqs.json

API

sam local start-api

It will start a localhost server on port 3000. To use different port use below command

sam local start-api -p 8000

Deployment

We can use SAM to deploy the lambda functions and create resources automatically - Details

Example

sam deploy --config-file sam/samconfig.toml --config-env dev

AWS Permissions

We need below roles with required permission in order to run SAM template.

Role for execute SAM deploy command

• S3 Access
• Cloudformation Access
• iam:PassRole Sample IAM Policy

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Statement1",
            "Effect": "Allow",
            "Action": [
                "iam:PassRole"
            ],
            "Resource": [
                "arn:aws:iam::1234567890:role/cloudformation-role"
            ]
        }
    ]
}

Role for cloudformation to create resources mentioned in SAM template

Add required permissions according to the resources added in the SAM template file.

Invoke Lambda

Lambda can be invoked in multiple ways. Following are few

• SQS
• function Url
• API Gateway
• AWS SKD eg. boto3

Invoke lambda without any external event trigger using boto3 - Details

Example code

import json
import boto3

# Create a Boto3 Lambda client
lambda_client = boto3.client('lambda')

# payload is optional
payload = {
    "key": "value"
}


# Invoke the Lambda function
# InvocationType="Event" -> just invoke
# InvocationType="RequestResponse" -> invoke and get function response
response = lambda_client.invoke(
    FunctionName="function_url_lambda",
    InvocationType="Event",
    Payload=json.dumps(payload)
)

print(response)

# if InvocationType is RequestResponse
response_data = response['Payload'].read()
print(json.loads(response_data))