MultipleHosting

Hosting Multiple MarkUs-App Instances on a Server

Say, one wants to host a Markus application per course offered by the CS department. Each single application instance would share the same application code (by facilitating symbolic links) and uses its own configuration (hence, database), log files and tmp directory. The architecture might be as follows. Apache acts as a reverse-proxy and establishes the connection the the locally listening mongrel clusters depending on the requested URL:

apache (or any other reverse proxy)
  |
  |
  `-> mongrel_cluster1: ports 8000-8002
  |-> mongrel_cluster2: ports 8003-8005
  \-> mongrel_cluster3: ports 8006-8008

Each mongrel cluster would serve the MarkUs application for one course. Say we would want to host the MarkUs apps on machine 'master.example.com'. The URI-scheme could then look like so:

http://master.example.com/markus/csc108/  # MarkUs for course 108
http://master.example.com/markus/csc209/  # MarkUs for course 209
http://master.example.com/markus/csc148/  # MarkUs for course 148

and so on.

One application will provide the "main" MarkUs application. All subsequent applications will use their own copy of configuration files, tmp and log directories with the rest of the application "symlinked" to the "main" MarkUs application. Next we assume the following directory structure for the "main" MarkUs app:

<path-to-main-markus-app>/
   app                  # application code
   config               # application configuration
   db                   # db-setup files
   doc
   lib                  # ruby/rails libraries
   log                  # directory where logging information goes
   public               # public files (might be configured as DocumentRoot when using Apache httpd)
   script               # rails utility scripts
   test                 # application tests
   tmp                  # pid-files, session-files, other temporary data
   vendor               # rails plugins, vendor code, etc.

These are the directories typically present for a Rails application. The public directory should be accessible by the Webserver. For information as to how to set up the "main" application, see the [deployment notes](wiki:InstallProd)

MarkUs applications running in parallel to the "main" application do not require their own copy of the Rails application code. In fact, they require their own copy of the following directories only:

<path-to-additional-markus-app>/
  config               # copy
  log                  # copy
  script               # copy
  tmp                  # copy

All other files and directories should be symlinked to the "main" MarkUs application. Hence the structure would look as follows:

<path-to-additional-markus-app>/
  app                  # symlink
  config               # copy
  db                   # symlink
  doc                  # symlink
  lib                  # symlink
  log                  # copy
  public               # symlink (not necessary actually, Webserver can be configured to serve those files from the main olm app)
  script               # copy
  test                 # symlink
  tmp                  # copy
  vendor               # symlink

Make sure the "tmp" directory of your "slim" MarkUs application contains a directory "pids". This is the place where mongrel places its PID files.

Edit the configurations for your second application. In particular make sure that you use a different database name in config/database.yml and make your course specific changes in config/environment.rb. Pay particular attention to the following lines:

# ignore URL prefix specified below
config.action_controller.relative_url_root = "/somepath"

The above line should say:

# ignore URL prefix specified below
config.action_controller.relative_url_root = "/markus/csc108"  # "main" app

Moreover, change the session cookie name of each MarkUs instance to a more specific name. Snippet:

config.action_controller.session = {
  :session_key => '_markus_session_csc108'

If the application is accessible by the URL "http://master.example.com/markus/csc108/". Also, change config/mongrel_cluster.yml so that the ports on which the mongrel servers are listening for this application do not overlap with any other configured MarkUs app. For the "main" application in our example the file would look like so:

log_file: log/mongrel.log
port: "8000"
environment: production
pid_file: tmp/pids/mongrel.pid
servers: 3

and for the additional MarkUs app as follows:

log_file: log/mongrel.log
port: "8003"
environment: production
pid_file: tmp/pids/mongrel.pid
servers: 3

Hence, the main application would listen on ports 8000-8002 on localhost, the additional application on ports 8003-8005 on localhost. Finally we need to tell the Webserver, what requests to pass on to what MarkUs application (what port-range). An exemplary Apache httpd config snipped would look as follows:

# mod_proxy (incl. mod_proxy_balancer required)
# Define proxy balancer(s); One per course
<Proxy balancer://mongrel_cluster_csc108>
   BalancerMember http://127.0.0.1:8000 retry=10
   BalancerMember http://127.0.0.1:8001 retry=10
   BalancerMember http://127.0.0.1:8002 retry=10
</Proxy>
<Proxy balancer://mongrel_cluster_csc209>
  BalancerMember http://127.0.0.1:8003 retry=10
  BalancerMember http://127.0.0.1:8004 retry=10
  BalancerMember http://127.0.0.1:8005 retry=10
</Proxy>

DocumentRoot /opt/markus-apps/markus-main/public
<Directory />
  Options FollowSymLinks
  AllowOverride None
</Directory>

# Directory should match DocumentRoot
<Directory /opt/markus-apps/markus-main/public>
  Options Indexes FollowSymLinks MultiViews
  AllowOverride None
  Order allow,deny
  allow from all
</Directory>
# Images, Stylesheets, JavaScripts and error pages amongst others are served by Apache
RewriteRule ^/markus/(?:csc108|csc209)/(404.html|500.html|422.html|favicon.ico|blank_iframe.html)$ /$1 [R=301,L]
RewriteRule ^/markus/(?:csc108|csc209)/((?:stylesheets|images|javascripts)/.*)$ /$1 [R=301,L]
# If requested files are not found in DocumentRoot, pass them on to the mongrels
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
RewriteRule ^/(markus/csc108.*)$ balancer://mongrel_cluster_csc108/$1 [P,QSA,L]
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
RewriteRule ^/(markus/csc209.*)$ balancer://mongrel_cluster_csc209/$1 [P,QSA,L]

Starting/Stopping of mongrel-clusters is documented in the [[deployment notes|InstallProdStable]].