_index.md 20 KB


title: "Development" date: 2019-03-13T18:28:09-07:00 draft: false

weight: 2

This section goes into greater detail on useful features within the Hue environment.

Building

Documentation

New website:

Install https://gohugo.io/getting-started/quick-start/ Make sure the base URL is correct:

cd docs/docs-site
vim config.toml
baseURL='http://cloudera.github.io/hue/docs-4.4.0/'

Build the doc website:

hugo server -wDs . -d ~/tmp/docs-4.4.0

Add it to the github page and push:

git checkout gh-pages
cp ~/tmp/docs-4.4.0 .
rm latest
ln -s docs-4.4.0 latest

git push origin HEAD:gh-pages

Old documentation:

make docs

Javascript

The javascript files are currently being migrated to webpack bundles, during this process some files will live under src/desktop/static/ and some will live under src/dekstop/js

For changes to the files under src/desktop/js the following applies:

First make sure all third-party dependencies defined in package.json are installed into node_modules/

npm install

Also run this after making changes to package.json, adding new third-party dependencies etc.

To generate the js bundles run:

npm run webpack
npm run webpack-workers
npm run webpack-login

During development the bundles can be autogenerated when it detects changes to the .js files, for this run:

npm run dev

Before sending a review with changes to the bundles run:

npm run lint-fix

and possibly fix any issues it might report.

CSS / LESS

After changing the CSS in a .less file, rebuilding with:

make css

SQL Autocomplete

Install a patched jison:

git clone https://github.com/JohanAhlen/jison
cd jison
npm install -g .

Then run:

make sql-all-parsers

Ace Editor

After modifying files under tools/ace-editor run the following to build ace.js

npm install
make ace

Internationalization

How to update all the messages and compile them:

make locales

How to update and compile the messages of one app:

cd apps/beeswax
make compile-locale

How to create a new locale for an app:

cd $APP_ROOT/src/$APP_NAME/locale
$HUE_ROOT/build/env/bin/pybabel init -D django -i en_US.pot -d . -l fr

User Management

Except for static content, request.user is always populated. It is a standard Django models.User object. If you were to set a breakpoint at the index() function in our calculator app, you will find:

>>> request.user
<User: test>
"Under the covers:" Django uses a notion called middleware that's called in between the request coming in and the view being executed. That's how request.user gets populated. There's also a middleware for Hue that makes sure that no pages are displayed unless the user is authenticated.

Configuration

Configuration File

Hue uses a typed configuration system that reads configuration files (in an ini-style format). By default, Hue loads all *.ini files in the build/desktop/conf directory. The configuration files have the following format:

# This is a comment
[ app_name ]          # Same as your app's name
app_property = "Pink Floyd"

[[ section_a ]]         # The double brackets start a section under [ app_name ]
a_weight = 80         # that is useful for grouping
a_height = 180

[[ filesystems ]]       # Sections are also useful for making a list
[[[ cluster_1 ]]]       # All list members are sub-sections of the same type
namenode_host = localhost
# User may define more:
# [[[ cluster_2 ]]]
# namenode_host = 10.0.0.1

Configuration Variables

Your application's conf.py is special. It provides access to the configuration file (and even default configurations not specified in the file). Using the above example, your conf.py should define the following:

  • A desktop.lib.conf.Config object for app_property, such as:

    MY_PROPERTY = Config(key='app_property', default='Beatles', help='blah')
    
    You can access its value by MY_PROPERTY.get().

  • A desktop.lib.conf.ConfigSection object for section_a, such as:

    SECTION_A = ConfigSection(key='section_a',

    help='blah',
    members=dict(
      AWEIGHT=Config(key='a_weight', type=int, default=0),
      AHEIGHT=Config(key='a_height', type=int, default=0)))
    

    You can access the values by SECTION_A.AWEIGHT.get().

  • A desktop.lib.conf.UnspecifiedConfigSection object for filesystems, such as:

    FS = UnspecifiedConfigSection(
      key='filesystems',
      each=ConfigSection(members=dict(

      nn_host=Config(key='namenode_host', required=True))
    

    An UnspecifiedConfigSection is useful when the children of the section are not known. When Hue loads your application's configuration, it binds all sub-sections. You can access the values by:
    cluster1_val = FS['cluster_1'].nn_host.get()
    all_clusters = FS.keys()
    for cluster in all_clusters:
      val = FS[cluster].nn_host.get()
    

Your Hue application can automatically detect configuration problems and alert the admin. To take advantage of this feature, create a config_validator function in your conf.py:

  def config_validator(user):
    """
    config_validator(user) -> [(config_variable, error_msg)] or None
    Called by core check_config() view.
    """
    res = [ ]
    if not REQUIRED_PROPERTY.get():
      res.append((REQUIRED_PROPERTY, "This variable must be set"))
    if MY_INT_PROPERTY.get() < 0:
      res.append((MY_INT_PROPERTY, "This must be a non-negative number"))
    return res
You should specify the help="..." argument to all configuration related objects in your conf.py. The examples omit some for the sake of space. But you and your application's users can view all the configuration variables by doing:
    $ build/env/bin/hue config_help
  

Running "Helper Processes"

Some Hue applications need to run separate daemon processes on the side.

Suppose your application needs a helper my_daemon.py. You need to register it by:

  • In setup.py, add to entry_points:

    entry_points = {
      'desktop.sdk.application': 'my_app = my_app',
      'desktop.supervisor.specs': [ 'my_daemon = my_app:SUPERVISOR_SPEC' ] }
    

  • In src/my_app/__init__.py, tell Hue what to run by adding:

    SUPERVISOR_SPEC = dict(django_command="my_daemon")
    

  • Then in src/my_app/management/commands, create __init__.py and my_daemon.py. Your daemon program has only one requirement: it must define a class called Command that extends django.core.management.base.BaseCommand. Please see kt_renewer.py for an example.

The next time Hue restarts, your my_daemon will start automatically. If your daemon program dies (exits with a non-zero exit code), Hue will restart it.

"Under the covers:" Threading. Hue, by default, runs CherryPy web server. If Hue is configured (and it may be, in the future) to use mod_wsgi under Apache httpd, then there would be multiple python processes serving the backend. This means that your Django application code should avoid depending on shared process state. Instead, place the stored state in a database or run a separate server.

Walk-through of a Django View

Django Flow

Django is an MVC framework, except that the controller is called a "view" and the "view" is called a "template". For an application developer, the essential flow to understand is how the "urls.py" file provides a mapping between URLs (expressed as a regular expression, optionally with captured parameters) and view functions. These view functions typically use their arguments (for example, the captured parameters) and their request object (which has, for example, the POST and GET parameters) to prepare dynamic content to be rendered using a template.

Templates: Django and Mako

In Hue, the typical pattern for rendering data through a template is:

from desktop.lib.django_util import render

def view_function(request):
  return render('view_function.mako', request, dict(greeting="hello"))

The render() function chooses a template engine (either Django or Mako) based on the extension of the template file (".html" or ".mako"). Mako templates are more powerful, in that they allow you to run arbitrary code blocks quite easily, and are more strict (some would say finicky); Django templates are simpler, but are less expressive.

Django Models

Django Models are Django's Object-Relational Mapping framework. If your application needs to store data (history, for example), models are a good way to do it.

From an abstraction perspective, it's common to imagine external services as "models". For example, the Job Browser treats the Hadoop JobTracker as a "model", even though there's no database involved.

Accessing Hadoop

It is common for applications to need to access the underlying HDFS. The request.fs object is a "file system" object that exposes operations that manipulate HDFS. It is pre-configured to access HDFS as the user that's currently logged in. Operations available on request.fs are similar to the file operations typically available in python. See webhdfs.py for details; the list of functions available is as follows: chmod, chown, exists, isdir, isfile, listdir (and listdir_stats), mkdir, open (which exposes a file-like object with read(), write(), seek(), and tell() methods), remove, rmdir, rmtree, and stats.

Making Your Views Thread-safe

Hue works in any WSGI-compliant container web server. The current recommended deployment server is the built-in CherryPy server. The CherryPy server, which is multi-threaded, is invoked by runcpserver and is configured to start when Hue's supervisor script is used. Meanwhile, runserver start a single-threaded testing server.

Because multiple threads may be accessing your views concurrently, your views should not use shared state. An exception is that it is acceptable to initialize some state when the module is first imported. If you must use shared state, use Python's threading.Lock.

Note that any module initialization may happen multiple times. Some WSGI containers (namely, Apache), will start multiple Unix processes, each with multiple threads. So, while you have to use locks to protect state within the process, there still may be multiple copies of this state.

For persistent global state, it is common to place the state in the database or on the Browser local storage.

Authentication Backends

Hue exposes a configuration flag ("auth") to configure a custom authentication backend. See See http://docs.djangoproject.com/en/dev/topics/auth/#writing-an-authentication-backend for writing such a backend.

In addition to that, backends may support a manages_passwords_externally() method, returning True or False, to tell the user manager application whether or not changing passwords within Hue is possible.

Authorization

Applications may define permission sets for different actions. Administrators can assign permissions to user groups in the UserAdmin application. To define custom permission sets, modify your app's settings.py to create a list of (identifier, description) tuples:

PERMISSION_ACTIONS = [
  ("delete", "Delete really important data"),
  ("email", "Send email to the entire company"),
  ("identifier", "Description of the permission")
]

Then you can use this decorator on your view functions to enforce permission:

@desktop.decorators.hue_permission_required("delete", "my_app_name")
def delete_financial_report(request):
  ...

Using and Installing Thrift

Right now, we check in the generated thrift code. To generate the code, you'll need the thrift binary version 0.9.0. Please download from http://thrift.apache.org/.

The modules using Thrift have some helper scripts like regenerate_thrift.sh for regenerating the code from the interfaces.

Profiling Hue Apps

Hue has a profiling system built in, which can be used to analyze server-side performance of applications. To enable profiling::

build/env/bin/hue runprofileserver

Then, access the page that you want to profile. This will create files like /tmp/useradmin.users.000072ms.2011-02-21T13:03:39.745851.prof. The format for the file names is /tmp/....prof.

Hue uses the hotshot profiling library for instrumentation. The documentation for this library is located at: http://docs.python.org/library/hotshot.html.

You can use kcachegrind to view the profiled data graphically::

$ hotshot2calltree /tmp/xyz.prof > /tmp/xyz.trace
$ kcachegrind /tmp/xyz.trace

More generally, you can programmatically inspect a trace::

#!/usr/bin/python
import hotshot.stats
import sys

stats = hotshot.stats.load(sys.argv[1])
stats.sort_stats('cumulative', 'calls')
stats.print_stats(100)

This script takes in a .prof file, and orders function calls by the cumulative time spent in that function, followed by the number of times the function was called, and then prints out the top 100 time-wasters. For information on the other stats available, take a look at this website: http://docs.python.org/library/profile.html#pstats.Stats

Django Models

Each app used to have its own model to store its data (e.g. a SQL query, a workflow). In Hue 3 a unification of all the models happened and any app now uses a single Document2 model: desktop/core/src/desktop/models.py. This enables to avoid simply re-use document creation, sharing, saving etc...

REST

Hue is Ajax based and has a REST API used by the browser to communicate (e.g. submit a query or workflow, list some S3 files, export a document...). Currently this API is private and subject to change but can be easily reused. You would need to GET /accounts/login to get the CSRF token and POST it back along username and password and reuse the sessionid cookie in next communication calls.

** With Python Request **

Hue is based on the Django Web Framework. Django comes with user authentication system. Django uses sessions and middleware to hook the authentication system into request object. HUE uses stock auth form which uses “username” and “password” and “csrftoken” form variables to authenticate.

In this code snippet, we will use well-known python “requests” library. we will first acquire “csrftoken” by GET “login_url”. We will create python dictionary of form data which contains “username”, “password” and “csrftoken” and the “next_url” and another python dictionary for header which contains the “Referer” url and empty python dictionary for the cookies. After POST request to “login_url” we will get status. Check the r.status_code. If r.status_code!=200 then you have problem in username and/or password.

Once the request is successful then capture headers and cookies for subsequent requests. Subsequent request.session calls can be made by providing cookies=session.cookies and headers=session.headers.

import requests

def login_djangosite():
 next_url = "/"
 login_url = "http://localhost:8888/accounts/login?next=/"

 session = requests.Session()
 r = session.get(login_url)
 form_data = dict(username="[your hue username]",password="[your hue password]",
                  csrfmiddlewaretoken=session.cookies['csrftoken'],next=next_url)
 r = session.post(login_url, data=form_data, cookies=dict(), headers=dict(Referer=login_url))

 # check if request executed successfully?
 print r.status_code

 cookies = session.cookies
 headers = session.headers

 r=session.get('http://localhost:8888/metastore/databases/default/metadata',
 cookies=session.cookies, headers=session.headers)
 print r.status_code

 # check metadata output
 print r.text

Read more about it here.

http://issues.cloudera.org/browse/HUE-1450 is tracking a more official public API.

Upgrade path

After upgrading the version of Hue, running these two commands will make sure the database has the correct tables and fields.

./build/env/bin/hue syncdb
./build/env/bin/hue migrate

Front-end Development

Developing applications for Hue requires a minimal amount of CSS (and potentially JavaScript) to use existing functionality. As covered above, creating an application for the Hue is a matter of creating a standard HTML application.

In a nutshell, front-end development in Hue is using Bootstrap and Knockout js to layout your app and script the custom interactions.

CSS Styles

Hue uses Bootstrap version 2.0 CSS styles and layouts. They are highly reusable and flexible. Your app doesn't have to use these styles, but if you do, it'll save you some time and make your app look at home in Hue.

On top of the standard Bootstrap styles, Hue defines a small set of custom styles in desktop/core/static/css/jhue.css.

Defining Styles for Your Application

When you create your application it will provision a CSS file for you in the static/css directory. For organization purposes, your styles should go here (and any images you have should go in static/art). Your app's name will be a class that is assigned to the root of your app in the DOM. So if you created an app called "calculator" then every window you create for your app will have the class "calculator". Every style you define should be prefixed with this to prevent you from accidentally colliding with the framework style. Examples:

/* the right way: */
.calculator p {
  /* all my paragraphs should have a margin of 8px */
  margin: 8px;
  /* and a background from my art directory */
  background: url(../art/paragraph.gif);
}
/* the wrong way: */
p {
  /* woops; we're styling all the paragraphs on the page, affecting
     the common header! */
  margin: 8px;
  background: url(../art/paragraph.gif);
}

Icons

You should create an icon for your application that is a transparent png sized 24px by 24px. Your settings.py file should point to your icon via the ICON variable. The create_desktop_app command creates a default icon for you.

If you do not define an application icon, your application will not show up in the navigation bar.

Hue ships with Twitter Bootstrap and Font Awesome 3 (http://fortawesome.github.io/Font-Awesome/) so you have plenty of scalable icons to choose from. You can style your elements to use them like this (in your mako template):

<!-- show a trash icon in a link -->
<a href="#something"><i class="icon-trash"></i> Trash</a>

Static files

For better performances, Hue uses the Django staticfiles app. If in production mode, if you edit some static files, you would need to run this command or make apps. No actions are needed in development mode.

./build/env/bin/hue collectstatic

Adding Interactive Elements to Your UI

Hue by default loads these JavaScript components:

  • Ko js
  • jQuery
  • Bootstrap

These are used by some Hue applications, but not loaded by default:

  • Knockout js (desktop/core/static/ext/js/knockout-min.js)
  • jQuery UI (desktop/core/static/ext/js/jquery/plugins/jquery-ui-autocomplete-1.8.18.min.js)

These standard components have their own online documentation, which we will not repeat here. They let you write interactive behaviors with little or no JavaScript.

Debugging Tips and Tricks

  • Set DESKTOP_DEBUG=1 as an environment variable if you want logs to go to stderr as well as to the respective log files.
  • Use runserver. If you want to set a CLI breakpoint, just insert __import__("ipdb").set_trace() into your code.
  • Django tends to restart its server whenever it notices a file changes. For certain things (like configuration changes), this is not sufficient. Restart the server whole-heartedly.
  • We recommend developing with the Chrome console.