You can achieve that by running a reverse proxy server (such as nginx) in front of the applications.

First, install nginx on your droplet that is hosting the containers:

sudo apt-get update
sudo apt-get install nginx

Then, for each application, create a server block:

sudo nano /etc/nginx/sites-available/app1.domain.com

and insert the following into the file (replace app1.domain.com and 2368 as needed):

server {
    listen 80;
    server_name app1.domain.com;

    location / {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header Host $http_host;
        proxy_set_header X-NginX-Proxy true;

        proxy_pass http://127.0.0.1:2368;
    }
}

Enable the server block:

sudo ln -s /etc/nginx/sites-available/app1.domain.com /etc/nginx/sites-enabled/

Once you have done that for all applications, restart nginx:

sudo service nginx restart