Inconsistent results making API call from AWS Lambda - node.js

Question

Let me just apologize for this abysmal code ahead of time. I have almost zero node experience, and write all of my JS with React apps and Elixir on the back end. I am struggling to write a correct Lambda function in NodeJS, and have basically cobbled something together from Googling/SO/trial and error, etc.
What I'm doing is the following:
User wants to upload a file so they send some info to back end.
Back end generates a presigned key.
Front end sends file to S3.
S3 fires event and Lambda executes
Lambda now checks for mimetype and if it's a bad file, will delete the file from the S3 bucket and make a DELETE API call to my backend to tell it to delete the row the photo upload belongs to.
Where I'm struggling is when I make the API call to my backend inside of the s3.deleteObject call, I am getting wildly inconsistent results. A lot of time it's sending two delete requests back to back in the same Lambda execution. Sometimes it's like it never even calls the backend and just runs and shows complete without really logging anything to Cloudwatch.
My code is as follows:
const aws = require('aws-sdk');
const s3 = new aws.S3({apiVersion: '2006-03-01'});
const fileType = require('file-type');
const imageTypes = ['image/gif', 'image/jpeg', 'image/png'];
const request = require('request-promise');
exports.handler = async (event, context) => {
// Get the object from the event and show its content type
const bucket = event.Records[0].s3.bucket.name;
const key = decodeURIComponent(
event.Records[0].s3.object.key.replace(/\+/g, ' ')
);
const params = {
Bucket: bucket,
Key: key,
};
try {
const {Body} = await s3.getObject(params).promise();
const fileBuffer = new Buffer(Body, 'base64');
const fileTypeInfo = fileType(fileBuffer);
if (
typeof fileTypeInfo !== 'undefined' &&
fileTypeInfo &&
imageTypes.includes(fileTypeInfo.mime)
) {
console.log('FILE IS OKAY.');
} else {
await s3
.deleteObject(params, function(err, data) {
console.log('FILE IS NOT AN IMAGE.');
if (err) {
console.log('FAILED TO DELETE.');
} else {
console.log('DELETED ON S3. ATTEMPTING TO DELETE ON SERVER.');
const url =
`http://MYSERVERHERE:4000/api/event/${params.Key.split('.')[0]}`;
const options = {
method: 'DELETE',
uri: url,
};
request(options)
.then(function(response) {
console.log('RESPONSE: ', response);
})
.catch(function(err) {
console.log('ERROR: ', err);
});
}
})
.promise();
}
return Body;
} catch (err) {
const message = `Error getting object ${key} from bucket ${bucket}. Make sure they exist and your bucket is in the same region as this function.`;
console.log(message);
throw new Error(message);
}
};
This has been driving me mad for days. Any help is appreciated to explain why I would be getting unexpected results from a Lambda function like this.

Answer 1

Please check after update your else part with proper await use
Please try below code.
exports.handler = async (event, context) => {
// Get the object from the event and show its content type
const bucket = event.Records[0].s3.bucket.name;
const key = decodeURIComponent(
event.Records[0].s3.object.key.replace(/\+/g, ' ')
);
const params = {
Bucket: bucket,
Key: key,
};
try {
const {Body} = await s3.getObject(params).promise();
const fileBuffer = new Buffer(Body, 'base64');
const fileTypeInfo = fileType(fileBuffer);
if (
typeof fileTypeInfo !== 'undefined' &&
fileTypeInfo &&
imageTypes.includes(fileTypeInfo.mime)
) {
console.log('FILE IS OKAY.');
} else {
await s3.deleteObject(params).promise(); //fail then catch block execute
console.log('DELETED ON S3. ATTEMPTING TO DELETE ON SERVER.');
const url =
`http://MYSERVERHERE:4000/api/event/${params.Key.split('.')[0]}`;
const options = {
method: 'DELETE',
uri: url,
};
let response = await request(options); ////fail then catch block execute
console.log(response);
}
return Body;
} catch (err) {
console.log(err);
const message = `Error getting object ${key} from bucket ${bucket}. Make sure they exist and your bucket is in the same region as this function.`;
console.log(message);
throw new Error(message);
}
};

Answer 2

S3 delete operation is eventual consistent in all regions.
Hence as par AWS (captured relevant info),
A process deletes an existing object and immediately attempts to read it. Until the deletion is fully propagated, Amazon S3 might return the deleted data.
A process deletes an existing object and immediately lists keys within its bucket. Until the deletion is fully propagated, Amazon S3 might list the deleted object.
Ref: https://docs.aws.amazon.com/AmazonS3/latest/dev/Introduction.html#ConsistencyModel