AWS Lambda: Determine Event Source from event object. Note that this is an approximation as anybody can send a payload that resembles the real thing.

get-lambda-event-source.js

function getLambdaEventSource(event) {
    if (event.Records && event.Records[0].cf) return 'isCloudfront';

    if (event.configRuleId && event.configRuleName && event.configRuleArn) return 'isAwsConfig';

    if (event.Records && (event.Records[0].eventSource === 'aws:codecommit')) return 'isCodeCommit';

    if (event.authorizationToken === "incoming-client-token") return 'isApiGatewayAuthorizer';

    if (event.StackId && event.RequestType && event.ResourceType) return 'isCloudFormation';

    if (event.Records && (event.Records[0].eventSource === 'aws:ses')) return 'isSes';

    if (event.pathParameters && event.pathParameters.proxy) return 'isApiGatewayAwsProxy';

    if (event.source === 'aws.events') return 'isScheduledEvent';

    if (event.awslogs && event.awslogs.data) return 'isCloudWatchLogs';

    if (event.Records && (event.Records[0].EventSource === 'aws:sns')) return 'isSns';

    if (event.Records && (event.Records[0].eventSource === 'aws:dynamodb')) return 'isDynamoDb';

    if (event.records && event.records[0].approximateArrivalTimestamp) return 'isKinesisFirehose';

    if (event.records && event.deliveryStreamArn && event.deliveryStreamArn.startsWith('arn:aws:kinesis:')) return 'isKinesisFirehose';

    if (event.eventType === 'SyncTrigger' && event.identityId && event.identityPoolId) return 'isCognitoSyncTrigger';

    if (event.Records && event.Records[0].eventSource === 'aws:kinesis') return 'isKinesis';

    if (event.Records && event.Records[0].eventSource === 'aws:s3') return 'isS3';

    if (event.operation && event.message) return 'isMobileBackend';
    
    if (event.Records && (event.Records[0].eventSource === 'aws:sqs')) return 'isSqs';

}

I would like to show this code block on my master thesis. Can you confirm that this code is licensed under public domain?
Alternatively, could you grant me permission to publish it?

For SQS:

if (event.Records && (event.Records[0].eventSource === 'aws:sqs')) return 'isSqs';

Guys, this slipped under my radar. I don't know why github does not send notifications for gists.
silvav: if it's still relevant for you, then yes you can use it under public domain.
CowChris: thanks, I'll add it

For Python: You can check this out https://gist.github.com/Necromancerx/abed07138690d37d170a6cf15b40d749. This is just based on your gist. Thank you.

Would you kindly add a if statement for a lambda being triggered by application load balancer?

For API Gateway HTTP:

if (event.requestContext && event.requestContext.resourceId) return 'isApiGatewayHttp';

This is probably not the best idea as it relies on AWS implementation details which may change.

Interesting and useful. I have struggled with the best approach to knowing my invoker. Although this may not persist well over time it is better than putting a caller flag in the payload. The only other option I see is multiple similar functions, which leads to logic sprawl but avoids the conditional overhead.

For SQS add this

elif 'Records' in event and len(event['Records']) > 0 and 'eventSource' in event['Records'][0] and event['Records'][0]['eventSource'] == 'aws:sqs':
return 'sqs'

if (event.requestContext.elb.targetGroupArn) return 'is ALBEvent'