idle event

There seems to be a use case with serverless functions, AWS Lambdas specifically:

You need to explicitly close the connection so the lambda can end properly, otherwise it will run until configured timeout is reached. And if you are doing many get/set calls you can't always know in a practical way which and when is the last one processed

let client;

function downloadXML(url) {
    return new Promise( //code to download, resolve/reject );
}

function saveToReds(key, data) {
    client.set(key, data);
}

exports.handler = async (event, context, callback) => {
    client = redis.createClient(elastiCacheRedis);
    someXML = await downloadXML(url);
    objectsArrayXmlElements = libxmljs.parseXmlString(someXML);

    objectsArrayXmlElements.forEach(
        /*do stuff, then call saveToRedis(key, data); */
    );

    client.unref();
}

The code above will fail to write the first time to redis because client.unref() seems to be called before the file is downloaded and parsed. The weird thing is the second time the lambda function is run it will write correctly.
Using process.nextTick() didn't seem to make any difference, exactly the same behaviour
The only way it did work as expected was calling client.unref() inside the idle event.

Start by examining the node-redis client’s idle event and unref() behavior, then reproduce the reported AWS Lambda flow with asynchronous set calls. Done should mean pending Redis writes complete reliably before the Lambda exits, without requiring a second invocation or manual idle-event workaround.