Capturing output from process spawned from NodeJS Lambda

Question

I'm trying to capture the output from an external program launched from an AWS Lambda written in NodeJS. Full example code below. Any test event would do since it's not really used.

exports.handler = async (event) => {
    console.log ("Entering lambda" + JSON.stringify(event))

    var spawn = require('child_process').spawnSync;

    child_process = spawn ('aws', [' --version'], {
        stdio: 'inherit',
        stderr: 'inherit',
        shell: true
    })

    console.log ("done");
    const response = {
        statusCode: 200,
        body: JSON.stringify('done'),
    };
    return response;
};

When I run it, I get the following as output (I removed the test event details for brevity, since it's irrelevant).

What I don't see is the results of the aws --version command that I expected (I'm using it to test the correct invocation of the AWS CLI, but any Linux command would do). The code does execute synchronously because if I replace the invocation with child_process = spawn ('sleep', ['1'], {, lambda's execution time grows to 1117.85 ms, so the one-second sleep happens. But there's nothing captured in the execution logs.

START RequestId: 0c1287e2-d2ee-4436-a577-bc8ec3608120 Version: $LATEST
2019-01-16T19:12:45.130Z    0c1287e2-d2ee-4436-a577-bc8ec3608120    Entering lambda {...}
2019-01-16T19:12:45.143Z    0c1287e2-d2ee-4436-a577-bc8ec3608120    done
END RequestId: 0c1287e2-d2ee-4436-a577-bc8ec3608120
REPORT RequestId: 0c1287e2-d2ee-4436-a577-bc8ec3608120  Duration: 13.29 ms  Billed Duration: 100 ms     Memory Size: 128 MB Max Memory Used: 20 MB  

Am I doing something wrong? Or is there any other way to capture the output (status code, stdio, stderr) for a Lambda written in NodeJS?

Answer 1

This works for me (node.js 8.10 runtime)

exports.handler = async (event) => {
    const spawnSync = require('child_process').spawnSync;
    const process = spawnSync('echo', ['hello', 'world'], {
        stdio: 'pipe',
        stderr: 'pipe'
    });
    console.log(process.status);
    console.log(process.stdout.toString());
};

When trying to run with aws, it throws a ENOENT error. In other words, the command is not available. As mentioned in the question comments by @jarmod, I also believe the awscli is not available in the Lambda container.

What is available is the SDK, so that you can require('aws-sdk'); without bundling it to your Lambda deployment package.

Answer 2

aws-cli is a python package and is not installed in a Lambda environment.
To verify my statement, you can type shell commands here http://www.lambdashell.com/ and check what is installed by default in your execution environment or check the official documentation.

Your code above returns no output, because trying to execute aws returns ENOENT, meaning the file is not available.

If you want to run aws inside your lambda function, you can follow these instructions : Call aws-cli from AWS Lambda

I would however question why do you want to do this ? The AWS-SDK is included in the local runtime environment and you can call any AWS API directly from your code, without the need to spawn a process and deal with stdin/stdout. I would strongly advise to not spawn aws cli from your code but rather use the SDK instead.

But, if you do want to run a process from Lambda and capture stdout and stderr, here is how I am doing it.

'use strict';

const childProcess = require('child_process');

/*
 * Handle the chile process and returns a Promise
 * that resoved when process finishes executing
 * 
 * The Promise resolves an  exit_code
 */ 
function handleProcess(process) {


    return new Promise((resolve, reject) => {
        process.stdout.on('data', (data) => {
            console.log(`stdout: ${data}`);
            console.log('stdout');
        });

        process.stderr.on('data', (data) => {
            console.log(`stderr: ${data}`);
        });

        process.on('close', (code) => {
            console.log(`child process exited with code ${code}`);
            if (code === 0) {
                resolve(code);
            } else {
                reject(code);
            }
        });
    });
}



exports.handler = (event, context, callback) => {

    // console.log(JSON.stringify(process.env, null, 2));
    // console.log(JSON.stringify(event, null, 2));

    return handleProcess(childProcess.spawn('ls', ['--version']))

        .then((exit_code) => {

            console.log(`exit_code = ${exit_code}`)
            let response = {
                statusCode: (0 == exit_code) ? 200 : 500,
                body: exit_code
            };                
            callback(null, response);

        })

        .catch((error) => {
            console.error(error);
            let response = {
                statusCode: 500,
                body: error
            };
            callback(null, response);
        });

}