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@jeshan
Last active June 23, 2023 13:01
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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.
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';
}
@gpmilliken
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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.

@gpmilliken
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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'

@bullett445
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if (event.requestContext.elb.targetGroupArn) return 'is ALBEvent'

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