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Simple Application Example

If you fetch the MogileFS::Server tarball from 2.46 or later, you will find an example/testapp/ directory with a few files in it. With this you will see how a barebones application would serve up files from MogileFS.

Overview Reminder

Before we begin, a quick reminder of the flow for how applications should serve files from MogileFS:

  • Browser issues "GET /foo" request to a perlbal load balancer
  • Perlbal routes the request to your application server (perl, php, ruby, etc)
  • Application asks a MogileFS tracker where the file is (or cache/etc).
  • Application returns magic 'X-REPROXY-URL: http://path/from/mogilefs/tracker' header.
  • Perlbal intercepts that header, and responds to the original Browser with the actual file.

This quick reminder to why it's done this way is for scalability, efficiency, and flexibility. The application server doesn't have to read the file and then return it. It has to find the paths and can then service other requests.

Perlbal can take its sweet time in returning data to the client. Perlbal could also remember the request and respond with the file without ever talking to the application. Also, for many other reasons we won't get into now :)

If you don't understand any of this, just read on below and see how it's done in practice.

Requirements

Requirements for the example application are a working MogileFS cluster, as you'd get from following InstallHowTo. You should also be familiar with CommandlineUsage, so you can upload and test files in MogileFS easily.

Finally, you need Plack installed for actually running the application. Install it the same way you've pulled in MogileFS::Server and friends.

cpanm Plack is a great an easy way to do this.

You might also need to install Perlbal::XS::HTTPHeaders to get perlbal to start. If you cannot do this, simply comment out the XS enable headers line from testapp-perlbal.conf

Starting Up Perlbal

First, review the testapp-perlbal.conf file. It has a few things that you may ignore, but a few things are key:

CREATE POOL testapp_pool
  POOL testapp_pool ADD 127.0.0.1:5000

This is where your application server will live. If this were a big website you'd have many POOL lines, one for each webserver.

  SET role = reverse_proxy
  SET pool = testapp_pool 
  SET listen = 0.0.0.0:7070
  SET enable_reproxy = on

These lines are the meat, defining that perlbal will listen on port 7070, and that reproxies (what mogilefs relies on) should be allowed.

To start up perlbal with this configuration:

$ perlbal -c examples/testapp/testapp-perlbal.conf

(note that for simplicity of testing you should leave these running in the foreground for now. use a few terminal sessions if you have to).

Starting The Application

The test app is extremely simple. It only talks in plain text and will only serve files as plain text.

First, open up testapp.psgi and edit two lines near the top.

my $TRACKERS = ['tracker1:7001'];
my $DOMAIN   = 'toast';

Replace these with what your tracker hostname/port actually is, and what your test domain actually is.

Assuming you have Plack installed already, and nothing else running on port 5000, starting it should be simple:

$ plackup examples/testapp/testapp.psgi
HTTP::Server::PSGI: Accepting connections at http://0:5000/

Uploading a File

CommandlineUsage goes into great depth on this. For simplicity:

$ echo "hello I am a test file" | mogupload --key="/hellotest" --file="-"

Fetching the File

If you were to attempt to navigate to http://127.0.0.1:5000/hellotest - your browser would get a cryptic empty response. If your application is designed better than this test app, it shouldn't even be possible to get a response unless first going through perlbal.

Now, fire up http://127.0.0.1:7070/hellotest' in your browser. Replace 127.0.0.1` as necessary if the test host is not local to you.

If all went well you should be greeted with "Hello I am a test file"!

Understanding the App

Now that you have it all running, you should take some time to read through the source of testapp.psgi, and try to understand the Perlbal configuration a bit. After Perlbal 1.77, it has a full manual included (perlbal Perlbal::Manual to see it).

The testapp.psgi file is heavily commented to explain each step. It is stripped down to be very barebones. For a real application you should use a full framework, and especially try to avoid relying on raw Plack :)

If you run into any trouble or have any questions, feel free to ask for help on the mailing list or #mogilefs on freenode IRC.