Watermarking an image on AWS Lambda with node.js and gm - node.js

Question

I'm trying to resize and watermark an image (downloaded from S3) in an AWS Lambda function.
The resizing part is working well, based on the sample code from the "getting started" project of AWS Lambda.
Now, I have a problem adding a watermark to my files.
On my local system, I can do this:
gm('martinrose.jpg')
.draw(['image Over 0,0 0,0 wm-bas.png'])
.write('brol.jpg', function(e){
console.log(e||'done');
});
And it works without problem.
In the Lambda environment, I added the wm-bas.png file to the zip file uploaded to Amazon, and it seems to be found by my js code (I tested using lstatSync), but the real watermarking does not work.
Here is the relevant part of what I do:
gm(response.Body).size(function(err, size) {
var scalingFactor = Math.min(
newSize / size.width,
newSize / size.height
);
var width = scalingFactor * size.width;
var height = scalingFactor * size.height;
var fs = require('fs');
var stats = fs.lstatSync('wm-bas.png');
console.log(stats); // this outputs meaningful info, so, the file exists
var ctx = this.resize(width, height);//this works
if (shouldWatermark)
{
console.log("trying to watermark");
ctx = ctx.draw(['image Over 0,0 0,0 wm-bas.png']) //this doesn't work, although the previous log is written
}
ctx.toBuffer(imageType, function(err, buffer)
{
if (err) {
next(err);
} else {
next(null, response.ContentType, buffer);
}
}
);
});
What am I missing? Why doesn't this work? Is it related to the fact that I save in a buffer and not in a file?
I import gm with this code, BTW:
var gm = require('gm')
.subClass({ imageMagick: true });

Answer 1

You need to package all of your node_modules with your Lambda deployment. Install your modules locally in your project and package them with your Lambda code. Another very important fact is Amazon Lambda still relies on installed system libraries. Your Node.js module may be using a library that may not be installed on the system where Lambda is executed, you need to package everything with your Lambda deployment.
See this official post about modules and
Node.js packages in Lambda

Answer 2

I have used "sharp" library before to add a text watermark with a custom font using a Nodejs lambda function. I wrote a story on Medium you can read Watermark with an AWS lambda
//...
const textedSVG = Buffer.from(`<svg xmlns="http://www.w3.org/2000/svg"
xml:lang="en"
height="40"
width="200">
<text
font-family="MyFont"
font-style="italic"
x="0" y="20" font-size="16" fill="#fff">
${process.env.WATERMARK_TEXT}
</text></svg>`);
let imgDst = sharp(origimage.Body);
var buffer = await imgDst
.composite([
{
input: textedSVG,
gravity: "southeast",
},
])
// Use the Sharp module to resize the image and save in a buffer.
.resize(width)
.jpeg({ quality: 70 }) //decrease the image quality
.toBuffer();
//...