Lambda nodejs cant connect to documentDB

Good morning all, I'm trying to connect with NodeJs to my documentdb cluster with mongoose without ssl: I get {"message":"Internal server error"} with ssl i get pem file not found {"message":"ENOENT: no such file or directory, open '/var/task/rds-combined-ca-bundle.pem'"}

Here is my code with ssl

import { APIGatewayProxyEvent, APIGatewayProxyResult } from 'aws-lambda'
import mongoose = require('mongoose')
import fs = require("fs")
import path = require("path")

export const lambdaHandler = async (event: APIGatewayProxyEvent): Promise<APIGatewayProxyResult> => {
  let response: APIGatewayProxyResult;
  try {
    const filePath = path.join(__dirname, 'rds-combined-ca-bundle.pem')
    const databaseUri = 'mongodb://myuser:mypassword@mycluster.docdb.amazonaws.com:27017/?ssl=true&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false'
    const client = await mongoose.connect(databaseUri, {
        ssl: true,
        sslValidate: false,
        sslCA: filePath,
        useNewUrlParser: true,
        useUnifiedTopology: true
    })

    // Return result
    response = { statusCode: 200, body: JSON.stringify({ test: 'test mongoose', client: client }) }
  } catch (err: unknown) {
    console.log('4',err)
    response = { statusCode: 500, body: JSON.stringify({ message: err.message }) }
  }
  return response;
}

Here is my code without ssl

import { APIGatewayProxyEvent, APIGatewayProxyResult } from 'aws-lambda'
import mongoose = require('mongoose')

export const lambdaHandler = async (event: APIGatewayProxyEvent): Promise<APIGatewayProxyResult> => {
  let response: APIGatewayProxyResult;
  try {
    const client = await mongoose.connect(
    'mongodb://myuser:mypassword@mycluster.docdb.amazonaws.com:27017/sample-database?replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false',
    {
     useNewUrlParser: true
    })
    //Return result
    response = { statusCode: 200, body: JSON.stringify({ test: 'test mongoose', client: client }) }
  } catch (err: unknown) {
    console.log('4',err)
    response = { statusCode: 500, body: JSON.stringify({ message: err.message }) }
  }
  return response;
}

Could you help me ? thank you sincerely