---
title: "Applications"
date: 2019-03-13T18:28:09-07:00
draft: false
weight: 5
---
Building a brand new application is more work but is ideal for creating a custom solution.
## Introduction and Overview
Hue leverages the browser to provide users with an environment for exploring
and analyzing data.
Build on top of the Hue SDK to enable your application to interact efficiently with
Hadoop and the other Hue services.
By building on top of Hue SDK, you get, out of the box:
+ Configuration Management
+ Hadoop interoperability
+ Supervision of subprocesses
+ A collaborative UI
+ Basic user administration and authorization
This document will orient you with the general structure of Hue
and will walk you through adding a new application using the SDK.
### From 30,000 feet

Hue, as a "container" web application, sits in between your Hadoop installation
and the browser. It hosts all the Hue Apps, including the built-in ones, and
ones that you may write yourself.
### The Hue Server

Hue is a web application built on the Django python web framework.
Django, running on the WSGI container/web server (typically CherryPy), manages
the url dispatch, executes application logic code, and puts together the views
from their templates. Django uses a database (typically sqlite)
to manage session data, and Hue applications can use it as well
for their "models". (For example, the saved Editor stores
saved queries in the database.)
In addition to the web server, some Hue applications run
daemon processes "on the side". Some examples are the `Celery Task Server`, `Celery Beat`.
### Interacting with Hadoop

Hue provides some APIs for interacting with Hadoop.
Most noticeably, there are python file-object-like APIs for
interacting with HDFS. These APIs work by making REST API or Thrift calls
the Hadoop daemons. The Hadoop administrator must enable these interfaces from
Hadoop.
### On the Front-End
Hue provides a front-end framework based on
[Bootstrap](http://twitter.github.com/bootstrap/) and
[Knockout js](http://knockoutjs.com/).
### An Architectural View

A Hue application may span three tiers: (1) the UI
and user interaction in the client's browser, (2) the
core application logic in the Hue web
server, and (3) external services with which applications
may interact.
The absolute minimum that you must implement (besides
boilerplate), is a
"Django [view](https://docs.djangoproject.com/en/1.11/#the-view-layer/)"
function that processes the request and the associated template
to render the response into HTML.
Many apps will evolve to have a bit of custom JavaScript and
CSS styles. Apps that need to talk to an external service
will pull in the code necessary to talk to that service.
### File Layout
The Hue "framework" is in ``desktop/core/`` and contains the Web components.
``desktop/libs/`` is the API for talking to various Hadoop services.
The installable apps live in ``apps/``. Please place third-party dependencies in the app's ext-py/
directory.
The typical directory structure for inside an application includes:
```
src/
for Python/Django code
models.py
urls.py
views.py
forms.py
settings.py
conf/
for configuration (``.ini``) files to be installed
static/
for static HTML/js resources and help doc
templates/
for data to be put through a template engine
locales/
for localizations in multiple languages
```
For the URLs within your application, you should make your own ``urls.py``
which will be automatically rooted at ``/yourappname/`` in the global
namespace. See ``apps/about/src/about/urls.py`` for an example.
## Pre-requisites
### Dependencies
* The OS specific dependencies listed [here](http://cloudera.github.io/hue/latest/admin-manual/manual.html)
* Python 2.7
* Django (1.11 included with our distribution)
* Hadoop (Apache Hadoop 2+)
* Java (Java 1.8)
* npm (6.4+)
### Recommended Reading / Important Technologies
The following are core technologies used inside of Hue.
* Python. Dive Into Python is one of
several excellent books on python.
* Django. Start with [The Django Tutorial](https://docs.djangoproject.com/en/1.11/intro/).
* [Thrift](http://incubator.apache.org/thrift/) is used for communication
between daemons.
* [Mako](http://www.makotemplates.org/) is the preferred templating language.
## Fast-Guide to Creating a New Hue Application
Now that we have a high-level overview of what's going on,
let's go ahead and create a new installation.
### Download, Unpack, Build Distro
The Hue SDK is available from [Github](http://github.com/cloudera/hue). Releases
can be found on the [download page](http://gethue.com/category/release/).
Releases are missing a few dependencies that could not be included because of
licencing issues. So if you prefer to have an environment ready from scratch,
it is preferable to checkout a particular release tag instead.
cd hue
## Build
make apps
## Run
build/env/bin/hue runserver
## Alternative run
build/env/bin/hue supervisor
## Visit http://localhost:8000/ with your web browser.
### Run "create_desktop_app" to Set up a New Source Tree
./build/env/bin/hue create_desktop_app calculator
find calculator -type f
calculator/setup.py # distutils setup file
calculator/src/calculator/__init__.py # main src module
calculator/src/calculator/forms.py
calculator/src/calculator/models.py
calculator/src/calculator/settings.py # app metadata setting
calculator/src/calculator/urls.py # url mapping
calculator/src/calculator/views.py # app business logic
calculator/src/calculator/templates/index.mako
calculator/src/calculator/templates/shared_components.mako
# Static resources
calculator/src/static/calculator/art/calculator.png # logo
calculator/src/static/calculator/css/calculator.css
calculator/src/static/calculator/js/calculator.js
Some apps are blacklisted on certain versions of CDH (such as the 'Spark' app) due to
certain incompatibilities, which prevent them loading from in Hue.
Check the hue.ini 'app_blacklist' parameter for details.
### Install SDK Application
As you'll discover if you look at calculator's setup.py,
Hue uses a distutils entrypoint to
register applications. By installing the calculator
package into Hue's python virtual environment,
you'll install a new app. The "app_reg.py" tool manages
the applications that are installed. Note that in the following example, the value after the
"--install" option is the path to the root directory of the application you want to install. In this
example, it is a relative path to "/Users/philip/src/hue/calculator".
./build/env/bin/python tools/app_reg/app_reg.py --install calculator --relative-paths
=== Installing app at calculator
Updating registry with calculator (version 0.1)
--- Making egg-info for calculator
If you'd like to customize the build process, you can modify (or even complete
rewrite) your own `Makefile`, as long as it supports the set of required
targets. Please see `Makefile.sdk` for the required targets and their
semantics.
Congrats, you've added a new app!
What was that all about?
virtualenv
is a way to isolate python environments in your system, and isolate
incompatible versions of dependencies. Hue uses the system python, and
that's about all. It installs its own versions of dependencies.
Entry Points
are a way for packages to optionally hook up with other packages.
You can now browse the new application.
# If you haven't killed the old process, do so now.
build/env/bin/hue runserver
And then visit http://localhost:8000/ to check it out!
You should see the app in the left menu.
### Customizing Views and Templates
Now that your app has been installed, you'll want to customize it.
As you may have guessed, we're going to build a small calculator
application. Edit `calculator/src/calculator/templates/index.mako`
to include a simple form and a Knockout viewmodel:
<%!from desktop.views import commonheader, commonfooter %>
<%namespace name="shared" file="shared_components.mako" />
%if not is_embeddable:
${commonheader("Calculator", "calculator", user, "100px") | n,unicode}
%endif
## Main body
%if not is_embeddable:
${commonfooter(messages) | n,unicode}
%endif
The template language here is Mako,
which is flexible and powerful. If you use the "`.html`" extension, Hue
will render your page using
Django templates
instead.
Note that we use Knockout.js to do the heavy lifting of this app.
Let's edit `calculator/src/calculator/views.py` to simply render the page:
#!/usr/bin/env python
from desktop.lib.django_util import render
def index(request):
return render('index.mako', request, {
'is_embeddable': request.GET.get('is_embeddable', False),
})
You can now go and try the calculator.
# Testing
## The short story
Install the mini cluster (only once):
./tools/jenkins/jenkins.sh slow
Run all the tests:
build/env/bin/hue test all
Or just some parts of the tests, e.g.:
build/env/bin/hue test specific impala
build/env/bin/hue test specific impala.tests:TestMockedImpala
build/env/bin/hue test specific impala.tests:TestMockedImpala.test_basic_flow
Jasmine tests:
npm run test
## Longer story
The ``test`` management command prepares the arguments (test app names)
and passes them to nose (django_nose.nose_runner). Nose will then magically
find all the tests to run.
Tests themselves should be named *_test.py. These will be found
as long as they're in packages covered by django. You can use the
unittest frameworks, or you can just name your method with
the word "test" at a word boundary, and nose will find it.
See apps/hello/src/hello/hello_test.py for an example.
### Helpful command-line tricks
To run tests that do not depend on Hadoop, use:
build/env/bin/hue test fast
To run all tests, use:
build/env/bin/hue test all
To run only tests of a particular app, use:
build/env/bin/hue test specific
E.g.
build/env/bin/hue test specific filebrowser
To run a specific test, use:
build/env/bin/hue test specific
E.g.
build/env/bin/hue test specific useradmin.tests:test_user_admin
Start up pdb on test failures:
build/env/bin/hue test --pdb --pdb-failure -s
Point to an Impalad and trigger the Impala tests:
build/env/bin/hue test impala impalad-01.gethue.com
### Create and run the Jasmine tests
Add them in a "spec" subfolder relative to the file under test and the filename of the test has to end with "Spec.js".
someFile.js <- File under test
├── spec/
│ ├── someFileSpec.js <- File containing tests
Run all the tests once with:
npm run test
Optionally to use Karma and headless chrome for the tests you can run
npm run test-karma
See ```desktop/core/src/desktop/js/spec/karma.config.js``` for various options
### Special environment variables
DESKTOP_LOGLEVEL=
level can be DEBUG, INFO, WARN, ERROR, or CRITICAL
When specified, the console logger is set to the given log level. A console
logger is created if one is not defined.
DESKTOP_DEBUG
A shorthand for DESKTOP_LOG_LEVEL=DEBUG. Also turns on output HTML
validation.
DESKTOP_PROFILE
Turn on Python profiling. The profile data is saved in a file. See the
console output for the location of the file.
DESKTOP_LOG_DIR=$dir
Specify the HUE log directory. Defaults to ./log.
DESKTOP_DB_CONFIG=$db engine:db name:test db name:username:password:host:port
Specify alternate DB connection parameters for HUE to use. Useful for
testing your changes against, for example, MySQL instead of sqlite. String
is a colon-delimited list.
TEST_IMPALAD_HOST=impalad-01.gethue.com
Point to an Impalad and trigger the Impala tests.
### Writing tests that depend on Hadoop
Use pseudo_hdfs4.py! You should tag such tests with "requires_hadoop", as follows:
from nose.plugins.attrib import attr
@attr('requires_hadoop')
def your_test():
...
### Jenkins Configuration
Because building Hadoop (for the tests that require it) is slow, we've
separated the Jenkins builds into "fast" and "slow". Both are run
via scripts/jenkins.sh, which should be kept updated with the latest
and greatest in build technologies.