Can not connect to database : Mongoose/MongoDB, virtual box - virtualbox

Question

Context
A MongoDB database runs on an Ubuntu Virtual Machine (VM).
An express server app serves a directory on my host machine (Windows 10).
This directory is shared with the VM.
Issue
I am trying to launch my express app locally without success.
On VM side, connecting to the database via the mongo shell works normally.
On the host side, i just used npm start to launch the app.
Do I need to do something else so my machine host/the app can communicate with the db in the VM ?
I have tried :
https://serverfault.com/questions/225155/virtualbox-how-to-set-up-networking-so-both-host-and-guest-can-access-internet
and
https://2buntu.com/articles/1513/accessing-your-virtualbox-guest-from-your-host-os/
...but it didn't work.
I get this error :
error with npm start
Thank you for you help

Answer 1

It seems that you are here mixing two things :
Connection to a remote database host on a Virtual Machine
Running an application on a Virtual Machine that communicates to a local database on the Virtual Machine too
From what you explains, it seems that your setup looks like this :
+-------------------------+ +------------------------+
| | | |
| Windows 10 host machine | -- Shared folder -| Virtual machine |
| | application | MongoDB running |
| | | |
+-------------------------+ +------------------------+
When you run npm run main on your host machine, the application needs to connect to the remote database using Virtual Machine network adresse. Sharing a folder with the Virtual Machine has no report with reaching database.
When you run npm run main on your local machine, you can connect using localhost
or Virtual machinbe network adresse.
Your issue is not related to npm or mongodb but on your Virtual Machine connection setup.
If the application runs on Windows 10, the easiest way to setup your Virtual Machine network and connect to database is to set Bridge adpater on the VirtualBox's VM settings.
Then, setting dhcp on the main network interface of your Ubuntu machine will provides you an address.
Edit /etc/networking/interfaces then restart network using sudo /etc/init.d/networking restart
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
auto enp0s3
iface enp0s3 inet dhcp
Use provided enp0s3 inet address to connect to your VM's database. To get the proivided adress, use ip addr on a shell.

Answer 2

#user7364588
i don't have the etc/networking/interfaces but etc/network/interfaces with only this message inside :
# ifupdown has been replaced by netplan(5) on this system. See
# /etc/netplan for current configuration.
# To re-enable ifupdown on this system, you can run:
# sudo apt install ifupdown
Should I still apply your advice or use netplan ?
Inside netplan, I have a file 50-cloud-init.yaml containing
network:
version: 2
renderer: networkd
ethernets:
eth0:
dhcp4: true
dhcp6: false
optional: true
nameservers:
addresses: [4.2.2.1, 4.2.2.2, 208.67.220.220]
ip addr :
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 08:00:27:e3:9f:67 brd ff:ff:ff:ff:ff:ff
inet 10.0.2.15/24 brd 10.0.2.255 scope global dynamic eth0
valid_lft 85581sec preferred_lft 85581sec
inet6 fe80::a00:27ff:fee3:9f67/64 scope link
valid_lft forever preferred_lft forever