Initial connection returns other errors than just "failed to connect to server X on first connect"

[thernstig]

Do you want to request a feature or report a bug?
bug (I am not 100% sure it is a bug though)

What is the current behavior?

Consider this example:

const log4js = require('log4js');
const mongoose = require('mongoose');

const logger = log4js.getLogger('mongodb');

const connections = [];

const ip = 'mongodb';
const port = 27017;
const uri1 = `mongodb://${ip}:${port}/$test`;

const options = {
  useNewUrlParser: true,
  useCreateIndex: true,
  reconnectTries: Number.MAX_VALUE,
  reconnectInterval: 5000
};

[uri1].forEach(uri => {
  const db = mongoose.createConnection(uri, options);
  db.catch(() => {}); // handle 'Unhandled promise rejection' warning
  connections.push(db);

  db.on('connected', () => {
    logger.info(`MongoDB client: connection initialized to ${uri}`);
  });

  db.on('error', err => {
    if (
      err.message &&
      err.message.match(/failed to connect to server .* on first connect/)
    ) {
      setTimeout(() => {
        logger.info(`MongoDB client: connection attempt to ${uri}`);
        db.openUri(uri).catch(() => {});
      }, 5000);
    } else {
      logger.error(`MongoDB client: error for database ${uri}: ${err}`);
    }
  });
});
module.exports = {
  db1: connections[0]
};

This worked fine in mongoose 5.0.7 if mongodb 3.6.3 had not been started. However upgrading to mongoose 5.5.2 I get new failures. I've seen both Error: getaddrinfo ENOTFOUND mongodb mongodb:27017 and Error: connect ECONNREFUSED 10.0.51.11:27017.

All this is launched with docker stack, so sometimes the above code is launched before the mongodb docker container. Hence why I need to do this check at all. But I do not want to add extra checks for all kind of errors that can happen like the ones above.

Is it to be exected that ENOTFOUND and ERCONNREFUSED can happen in these scenarios, or should mongoose always report failed to connect to server .* on first connect during the first start-up attempts?

If the current behavior is a bug, please provide the steps to reproduce.

1. Put the above code in a file and build it in a docker container.
2. Start docker compose (or a docker stack) with mongodb as the only service and the built docker in step 1 as a service and start up the stack.

What is the expected behavior?
I was expecting failed to connect to server .* on first connect to always be returned during initial connect to mongodb in case the mongodb service is not completely up, not matter the state the service is in.

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.
Node.js: 10.13.0
Mongoose: 5.5.2
MongoDB: 3.6.3

[thernstig]

I still have no idea if this is a bug or not, but I re-wrote my code to better account for any errors on initial connection.

[vkarpov15]

We'll take a look and see if this is expected behavior or not. But realistically, we don't use docker, so if it turns out this issue only happens with docker we'll have to close it.

[vkarpov15]

I opened a PR in the mongodb driver for this ☝️