AWS Lambda Error: Could not unzip uploaded file

ZipFile needs to be a Buffer.

That means you have to read the file and convert it to a Buffer object.

You can use fs.readFile() or fs.readFileSync() to do this.

Your ZipFile params is incorrect, it must be a buffer. Try change to :

var fs = require('fs');

var params = {
    FunctionName: 'FunctionName',
    ZipFile: fs.readFileSync('deploy_package.zip')
}

lambda.updateFunctionCode(params, function(err, data) {
    if (err) console.log(err, err.stack);
    else console.log(data);
});