Here's how to get an instance of MongoDB up and running on your Opalstack server:

Create a shell user and make a note of the shell username. I'll use myuser as the username in the remainder of this procedure.
Create a "proxy port" application and make a note of the app name its port assignment. I'll use mongoapp and port 55555 in the remainder of this procedure.

SSH to your shell user from step 1 and run the following commands:

cd ~/apps/mongoapp
wget https://fastdl.mongodb.org/linux/mongodb-linux-x86_64-rhel70-4.4.1.tgz
tar zxf mongodb-linux-x86_64-rhel70-4.4.1.tgz
ln -s $PWD/mongodb-linux-x86_64-rhel70-4.4.1 mongodb
wget https://downloads.mongodb.com/compass/mongosh-1.8.0-linux-x64.tgz
tar zxf mongosh-1.8.0-linux-x64.tgz
ln -s $PWD/mongosh-1.8.0-linux-x64 mongosh
mkdir data
./mongodb/bin/mongod --dbpath $PWD/data --port 55555 --logpath $HOME/logs/apps/mongoapp/mongo.log --pidfilepath $PWD/pid --fork

The MongoDB server is now running in the background. Connect to it and create your Mongo superuser with the following commands:

~/apps/mongoapp/mongosh/bin/mongosh localhost:55555/admin
# you're now in the mongo shell, next command creates your mongo superuser
# replace USERNAME and PASSWORD with your desired mongo username and pw
db.createUser({user: "USERNAME", pwd: "PASSWORD", roles: [ "root" ]})
# verify that it was created
show users
# then exit
exit

Finally, stop the running mongodb process and restart it with auth enabled:

kill $( cat $HOME/apps/mongoapp/pid)
$HOME/apps/mongoapp/mongodb/bin/mongod --dbpath $HOME/apps/mongoapp/data --port 55555 --logpath $HOME/logs/apps/mongoapp/mongo.log --pidfilepath $HOME/apps/mongoapp/pid --fork --auth

Your MongoDB instance is now running in the background waiting for authenticated connections.

You'll probably want to reconnect as your superuser from step 4 above to create less-privileged users with the roles necessary for your application:

~/apps/mongoapp/mongodb/bin/mongo localhost:55555/admin --username USERNAME

Please refer to the MongoDB docs for how to create additional users: MongoDB: Add Users

Here are the commands to start and stop it:

Start: $HOME/apps/mongoapp/mongodb/bin/mongod --dbpath $HOME/apps/mongoapp/data --port 55555 --logpath $HOME/logs/apps/mongoapp/mongo.log --pidfilepath $HOME/apps/mongoapp/pid --fork --auth
Stop: kill $( cat $HOME/apps/mongoapp/pid)

That's it - now go forth and Mongo! 🍃