I know two ways:
1-) First Form:
You could take a machine from AWS, Azure or Digital Ocean and install the two applications on it and mongodb as well.
In this video the guy explains how to deploy a nodejs application with free SSL and explains some parts of server security as well:
https://www.youtube.com/watch?v=kR06NoSzAXY
To make the issue of /admin redirecting to another app, just see the Nginx rules to redirect to the other application.
Using this video I deployed a Nodejs+Mongo application to AWS and it worked well.
2-) The second form is:
You can use share hosting, which is the widely used shared hosting for small websites in PHP, has an answer in English that explains how to do:
https://stackoverflow.com/questions/24777750/how-to-host-a-node-js-application-in-shared-hosting
The author of the best answer created a project called Node.php on github, it might be interesting to take a look at the project and maybe even mongodb vc can install it this way.
I’ve never used nodejs this way (share hosting), I used a machine in AWS’s free Ier and met me for a specific project, on the digital Ocean vc spends $5 and has one or two months free and on AWS you have one year free.
It is up to you to evaluate the need of the application, as the number of users, requests in the database and other things, because AWS is expensive, the free Tier machine after a year are charged 20$ per month, in the digital Ocean are 5$, but I think it is a more modest machine and you have to consider that are the two app + a bank, maybe it is interesting to take a machine only for the database.
Edit:
The umbler has a very nice price to start(6 REAL per application in the most basic package of them the PP) also and they have nodejs+mongodb hosting, compensates vc of a look tb.
Yes, it is possible, there are several Clouds for hosting, one with certain restrictions but free and easy to use, like Heroku, I recommend that you study about.
– BrTkCa
Great Lucas Costa, thank you!
– Marzine