Why is UnhandledPromiseRejectionWarning only appearing in production (Google Cloud Run)? - node.js

Question

I am having a very hard time trying to solve a few functions that work perfectly fine on my laptop development environment (even if I run it with NODE_ENV=production) but when I deploy it to Google Cloud Run I get errors such as
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2021-12-15T12:16:35.016406Z at TCP.done (_tls_wrap.js:564:7)
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2021-12-15T12:16:35.016414Z(Use `node --trace-warnings ...` to show where the warning was created)
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2021-12-15T12:16:35.016426Z(node:1) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
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2021-12-15T12:16:35.116284Z(node:1) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
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2021-12-15T12:16:35.116931Z(node:1) UnhandledPromiseRejectionWarning: Error: socket hang up
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2021-12-15T12:16:35.116954Z at connResetException (internal/errors.js:639:14)
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2021-12-15T12:16:35.116969Z at TLSSocket.socketCloseListener (_http_client.js:449:25)
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2021-12-15T12:16:35.116979Z at TLSSocket.emit (events.js:412:35)
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2021-12-15T12:16:35.116989Z at net.js:686:12
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2021-12-15T12:16:35.116999Z at TCP.done (_tls_wrap.js:564:7)
causing my script to halt. In my local version it continues without stopping. It is very frustrating as I need to upload the code to Cloud Run all the time in order to test my code. I am testing it blindly as the errors do not appear in my development version.
I am quite new to Node.js and are constantly having a hard time with .then(), chaining .then(), promises, using resolve() so the code is likely to be wrong.
My questions here:
Why is this error only appearing on Cloud Run?
How can I configure my local computer the same way so it shows the same warnings and errors - so I can troubleshoot this?
My code (simplified):
function createOrUpdateSpotterData(data) {
// NOTE: Data comes from API and not from DB, thus no info such as twitter_status
// TODO: Separate into a create or update, in order to not check twitter ID every time.
return new Promise( async function (resolve) {
var twitterId = await twitterApi.getTwitterIdFromUsername(cleanedUsername)
data['twitter_numeric'] = twitterId
resolve(data)
}).then( (data) => {
db.collection('spotters').doc(data.marker).set(data)
}).catch( (error) => { console.log(error) })
}
async function updateSpottersJsonToDb() {
console.log("> updateSpottersJsonToDb")
return new Promise( (resolve, reject) => {
readStorageData(remote_files['spotters'])
.then( async (spotterListJson) => {
var spotterList = JSON.parse(spotterListJson)
await spotterList.forEach((spotter) => {
createOrUpdateSpotterData(spotter)
})
})
.then(() => {
resolve()
})
.catch((error) => {console.error(error)})
}).catch((error) => {console.error(error)})

Answer 1

It is quite embarrasing to admit but I was a bit overwhelmed by the quantity of this 'error message' that I could not see the forest for the trees. It was after all just a warning and by filtering the logs (on Google Cloud Logs) on std.out I realized this was not causing any of the issues I was having in my application.
The cause of this issue however was that I was not catching errors in my Promises correctly, which is really another issue (being discussed here).
If you find this through Google later on, it could be good to know that you can surpress this warning with process.on().