Automatically generate thumbnail images triggered by S3 image upload using AWS lambda

Do not check enable trigger.
Enable it manually after checking the operation of the function that will be written later.
When you have finished entering your information, click Next.

We will actually write the function on this screen.
There is a field to enter the function name, but you can use any name you like.
Since we selected "s3-get-object" on the blueprint selection screen,
the code to retrieve the file from S3 has been written in advance.

'use strict'; console.log('Loading function'); const aws = require('aws-sdk'); const s3 = new aws.S3({ apiVersion: '2006-03-01' }); exports. handler = (event, context, callback) => { //console.log('Received event:', JSON.stringify(event, null, 2)); // 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, }; s3.getObject(params, (err, data) => { if (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); callback(message); } else { console.log('CONTENT TYPE:', data.ContentType ); callback(null, data.ContentType); } }); };

However, if this continues, you will be able to retrieve files from S3, but you
will not be able to generate thumbnail images.
I'll add a little bit to this code.

'use strict'; console.log('Loading function'); var fs = require('fs'); var im = require('imagemagick'); const aws = require('aws-sdk'); const s3 = new aws.S3({ apiVersion: '2006-03-01' }); exports.handler = (event, context, callback) => { 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, }; s3.getObject(params, ( err, data) => { if (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); callback(message); } else { var contentType = data.ContentType; var extension = contentType.split('/').pop(); console.log(extension); im.resize({ srcData: data.Body, format: extension, width: 100 }, function(err, stdout, stderr) { if (err) { context.done('resize failed', err); } else { var thumbnailKey = key.split('.')[0] + "-thumbnail." + extension; s3.putObject({ Bucket: bucket, Key: thumbnailKey, Body: new Buffer(stdout, 'binary'), ContentType: contentType }, function(err, res) { if (err) { context.done('error putting object', err); } else { callback(null, "success putting object"); } }); } }); } }); };

Once added, it will look like this.
The process is the same until the file is retrieved from S3, but
the retrieved image is resized using imagemagick and the
processed image is uploaded to S3 again as a thumbnail image.

After writing the code, configure the IAM Role as shown below.For
now, let's skip this part and automatically create a new Role from the template.
The policy for manipulating S3 objects will be attached to the role created here, so
if you do not set it correctly, the function may result in an error.
(Access Denied is a common problem due to lack of access privileges to S3)

When you click Next, a confirmation screen will appear, so press the "Create function" button.
Then a lambda function will be created.

The function you just created is displayed in the list!

③Function operation test

Test whether the function you created works correctly.

Select Test Event Settings from the actions at the top of the screen.

The test event input screen will then appear.
The test event is written in json format, but
please consider that lambda receives this json from S3 and executes the function.

we will test whether the lambda function works properly by assuming that we have uploaded an image file called test.jpg to an S3 bucket in advance and

A template is also provided for this test event, so
let's use the template called S3 Put.
Enter the following and click Save and Test.

{ "Records": [ { "eventVersion": "2.0", "eventTime": "1970-01-01T00:00:00.000Z", "requestParameters": { "sourceIPAddress": "*" }, "s3": { "configurationId": "testConfigRule", "object": { "eTag": "0123456789abcdef0123456789abcdef", "sequencer": "0A1B2C3D4E5F678901", "key": "test.jpg", "size": 1024 }, "bucket" : { "arn": "arn:aws:s3:::lambda-img-resize", "name": "lambda-img-resize", "ownerIdentity": { "principalId": "EXAMPLE" } }, " s3SchemaVersion": "1.0" }, "responseElements": { "x-amz-id-2": "EXAMPLE123/5678abcdefghijklambdaisawesome/mnopqrstuvwxyzABCDEFGH", "x-amz-request-id": "EXAMPLE123456789" }, "awsRegion": "ap-northeast-1", "eventName": "ObjectCreated:Put", "userIdentity": { "principalId": "EXAMPLE" }, "eventSource": "aws:s3" } ] }

A message was returned when the execution was successful!
Let's check if there are any changes in the contents of the S3 bucket.

Yes, the thumbnail image is being generated as if nothing had happened.
There seems to be no problem with the function execution itself.

④Lambda trigger settings

Finally, in the final stage, we will set the trigger.
The previous step was just a test, so
even if you upload a new image at this stage, a thumbnail image will not be created.
You need to set up a trigger so that the function runs automatically when the image is uploaded.
Click the Trigger tab from the lambda function you created.

The trigger itself was created when creating the function, so all that is left is to enable it.
Click Activate.

⑤Operation confirmation

Now, let's actually upload the image to S3 and check it.

・・・・・・It's been created, it's wonderful. . .

■Summary

What did you think?
It's a little complicated because you have to write code, but
it's convenient and interesting because you can do this without needing EC2.
This time I just touched on it briefly, but I'd like to try something a little more advanced.
That's all, thank you very much.

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