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Oliver Gorwits
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Netdisco/lib/App/Netdisco/Manual/Developing.pod
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Netdisco/lib/App/Netdisco/Manual/Developing.pod
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=head1 NAME
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App::Netdisco::Manual::Developing - Notes for contributors
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=head1 DEVELOPER NOTES
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This document aims to help developers understand the intent and design of the
|
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code within Netdisco. Patches and feedback are always welcome :-)
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=head1 Introduction
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This release of Netdisco is built as a L<Dancer> application, and uses many
|
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modern technologies and techniques. Hopefully this will make the code easier
|
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to manage and maintain in the long term.
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Although Dancer is a web application framework, it provides very useful tools
|
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for command line applications as well, namely configuration file management
|
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and database connection management. We make use of these features in the
|
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daemon and deployment scripts.
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Overall the application tries to be as self-contained as possible without also
|
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needing an excessive number of CPAN modules to be installed. However, Modern
|
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Perl techniques have made dependency management almost a non-issue, and
|
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Netdisco can be installed by and run completely within an unprivileged user's
|
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account, apart from the PostgreSQL database setup.
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|
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Finally the other core component of Netdisco is now a L<DBIx::Class> layer for
|
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database access. This means there is no SQL anywhere in the code, but more
|
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important, we can re-use the same complex queries in different parts of
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Netdisco.
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The rest of this document discusses each "interesting" area of the Netdisco
|
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codebase, hopefully in enough detail that you can get hacking yourself :-)
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=head1 Versioning
|
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This is Netdisco major version 2. The minor version has six digits, which are
|
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split into two components of three digits each. It's unlikely that the major
|
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version number (2) will increment. Each "feature" release to CPAN will
|
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increment the first three digits of the minor version. Each "bug fix" release
|
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will increment the second three digits of the minor version.
|
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|
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Stable releases will have an even "feature" number. Beta releases will have an
|
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odd "feature" number and also a suffix with an underscore, to prevent CPAN
|
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indexing the distribution. Some examples:
|
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|
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2.002002 - "feature" release 2, "bug fix" release 2
|
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2.002003 - another bug was found and fixed, hence "bug fix" release 3
|
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2.003000_001 - first beta for the next "feature" release
|
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2.003000_002 - second beta
|
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2.004001 - the next "feature" release
|
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|
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|
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=head1 Global Configuration
|
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Dancer uses YAML as its standard configuration file format, which is flexible
|
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enough for our needs, yet still simple to edit for the user. We no longer need
|
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a parser as in the old version of Netdisco.
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At the top of scripts you'll usually see something like:
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use App::Netdisco;
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use Dancer ':script';
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First, this uses C<App::Netdisco>, which is almost nothing more than a
|
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placeholder module (contains no actual application code). What it does is set
|
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several environment variables in order to locate the configuration files.
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|
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Then, when we call "C<use Dancer>" these environment variables are used to
|
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load two YAML files: C<config.yml> and C<< <environment>.yml >> where
|
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C<< <environment> >> is typically either C<deployment> or C<development>.
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|
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The concept of "environments" allows us to have some shared "master" config
|
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between all instances of the application (C<config.yml>), and then settings
|
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for specific circumstances. Typically this might be logging levels, for
|
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example. The default file which C<App::Netdisco> loads is C<deployment.yml>
|
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but you can override it by setting the "C<DANCER_ENVIRONMENT>" environment
|
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variable.
|
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|
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The file is located in an C<environments> folder which defaults to being in
|
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the user's home directory. The name (or full path) of the folder can be
|
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overriden using the "C<DANCER_ENVDIR>" environment variable. The location of
|
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the folder alone can be overridden using the "C<NETDISCO_HOME>" environment
|
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variable.
|
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|
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Dancer loads the config using YAML, merging data from the two files. Config is
|
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made available via Dancer's C<setting('foo')> subroutine, which is exported.
|
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So now the C<foo> setting in either config file is easily accessed.
|
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|
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Another line commonly seen in scripts is this:
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use Dancer::Plugin::DBIC 'schema';
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|
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This plugin saves a lot of effort by taking some database connection
|
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parameters from the configuration file, and instantiating DBIx::Class database
|
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connections with them. The connections are managed transparently so all we
|
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need to do to access the Netdisco database, with no additional setup, is:
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schema('netdisco')->resultset(...)->search({...});
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=head1 DBIx::Class Layer
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DBIx::Class, or DBIC for short, is an Object-Relational Mapper. This means it
|
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abstracts away the SQL of database calls, presenting a Perl object for each
|
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table, set of results from a query, table row, etc. The advantage is that it
|
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can generate really smart SQL queries, and these queries can be re-used
|
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throughout the application.
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The DBIC layer for Netdisco is based at L<App::Netdisco::DB>. This is the
|
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global schema class and below that, under L<App::Netdisco::DB::Result> is a
|
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class for each table in the database. These contain metadata on the columns
|
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but also several handy "helper" queries which can be called. There are also
|
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C<ResultSet> classes which provide additional "pre-canned" queries.
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|
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Netdisco's DBIx::Class layer has excellent documentation which you are
|
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encouraged to read, particularly if you find it difficult to sleep.
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=head2 Results and ResultSets
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In DBIC a C<Result> is a table and a C<ResultSet> is a set of rows retrieved
|
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from the table as a result of a query (which might be all the rows, of
|
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course). This is why we have two types of DBIC class.
|
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Items in the C<Result> generally relate to the single table
|
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directly, and simply. In the C<ResultSet> class are more complex search
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modifiers which might synthesize new "columns" of data (e.g. formatting a
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timestamp) or subroutines which accept parameters to customize the query.
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However, regardless of the actual class name, you access them in the same way.
|
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For example the C<device> table has an L<App::Netdisco::DB::Result::Device>
|
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class and also an L<App::Netdisco::DB::ResultSet::Device> class. DBIC merges
|
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the two:
|
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schema('netdisco')->resultset('Device')->get_models;
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=head2 Virtual Tables (VIEWs)
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Where we want to simplify our application code even further we can either
|
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install a VIEW in PostgreSQL, or use DBIx::Class to synthesize the view
|
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on-the-fly. Put simply, it uses the VIEW definition as the basis of an SQL
|
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query, yet in the application we treat it as a real table like any other.
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Some good examples are a fake table of only the active Nodes (as opposed to
|
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all nodes), or the more complex list of all ports which are connected together
|
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(C<DeviceLink>).
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|
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All these tables live under the
|
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L<App::Netdisco::DB::Result::Virtual> namespace, and so you
|
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access them like so (for the C<ActiveNode> example):
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schema('netdisco')->resultset('Virtual::ActiveNode')->count;
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=head2 Versioning and Deployment
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To manage the Netdisco schema in PostgreSQL we use DBIx::Class's deployment
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feature. This attaches a version to the schema and provides all the code to
|
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check the current version and do whatever is necessary to upgrade.
|
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The schema version is stored in a new table called
|
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C<dbix_class_schema_versions>, although you should never touch it.
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The C<netdisco-db-deploy> script included in the distribution performs the
|
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following services:
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|
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* Installs the dbix_class_schema_versions table
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* Upgrades the schema to the current distribtion's version
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This works both on an empty, new database, and a legacy database from the
|
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existing Netdisco release, in a non-destructive way. For further information
|
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see L<DBIx::Class::Schema::Versioned> and the C<netdisco-db-deploy> script.
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|
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The files used for the upgrades are shipped with this distribution and stored
|
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in the C<.../App/Netdisco/DB/schema_versions> directory. They are generated
|
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using the C<nd-dbic-versions> script which also ships with the distribution.
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|
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=head2 Foreign Key Constraints
|
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|
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We have not yet deployed any FK constraints into the Netdisco schema. This is
|
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partly because the current poller inserts and deletes entries from the
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database in an order which would violate such constraints, but also because
|
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some of the archiving features of Netdisco might not be compatible anyway.
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|
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Regardless, a lack of FK constraints doesn't upset DBIx::Class. The
|
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constraints can easily be deployed in a future release of Netdisco.
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=head1 Web Application
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|
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The Netdisco web app is a "classic" Dancer app, using most of the bundled
|
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features which make development really easy. Dancer is based on Ruby's Sinatra
|
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framework. Its style is for many "helper" subroutines to be exported into the
|
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application namespace, to do things such as access request parameters,
|
||||
navigate around the "handler" subroutines, manage response headers, and so on.
|
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|
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Pretty much anything you want to do in a web application has been wrapped up
|
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by Dancer into a neat helper routine that does the heavy lifting. This
|
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includes configuration and database connection management, as was discussed
|
||||
above. Also, templates can be executed and Netdisco uses the venerable
|
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L<Template::Toolkit> engine for this.
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|
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Like most web frameworks Dancer has a concept of "handlers" which are
|
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subroutines to which a specific web request is routed. For example if the user
|
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asks for "C</device>" with some parameters, the request ends up at the
|
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L<App::Netdisco::Web::Device> package's "C<get '/device'>" handler. All this
|
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is done automatically by Dancer according to some simple rules. There are also
|
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"wrapper" subroutines which we use to do tasks such as setting up data lookup
|
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tables, and handling authentication.
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|
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Dancer also supports AJAX very well, and it is used to retrieve most of the
|
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data in the Netdisco web application in a dynamic way, to respond to search
|
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queries and avoid lengthy page reloads. You will see the handlers for AJAX
|
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look similar to those for GET requests but do not use Template::Toolkit
|
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templates.
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|
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Compared to the current Netdisco, the handler routines are very small. This is
|
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because (a) they don't include any HTML - this is delegated to a template, and
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(b) they don't include an SQL - this is delegated to DBIx::Class. Small
|
||||
routines are more manageable, and easier to maintain. You'll also notice use
|
||||
of modules such as L<Net::MAC> and L<NetAddr::IP::Lite> to simplify and make
|
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more robust the handling of data.
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|
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In fact, many sections of the web application have been factored out into
|
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separate Plugin modules. For more information see the
|
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L<App::Netdisco::Web::Plugin> manual page.
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=head2 Running the Web App
|
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|
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Dancer apps conform to the "PSGI" standard interface for web applications,
|
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which makes for easy deployment under many stacks such as Apache, FCGI, etc.
|
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See L<Dancer::Deployment> for more detail.
|
||||
|
||||
At a minimum Netdisco can run from within its own user area as an unprivileged
|
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user, and actually ships with a fast, preforking web server engine. The
|
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C<netdisco-web> script uses L<Daemon::Control> to daemonize this simple web
|
||||
server so you can fire-and-forget the Netdisco web app without much trouble at
|
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all. This script in turn calls C<netdisco-web-fg> which is the real Dancer
|
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application, that runs in the foreground if called on its own.
|
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|
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All web app code lives below L<App::Netdisco::Web>, but there are also some
|
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helper routines in L<App::Netdisco::Util::Web> (for example sorting device
|
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port names).
|
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|
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If you're working on code in the web application, it's possible to have the
|
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app restart itself each time you save a file in your editor. The following
|
||||
command will watch the C<lib> and C<share> folder trees for changes, and you
|
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probably want to switch to the C<development.yml> dancer configuration for
|
||||
additional logging:
|
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|
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DANCER_ENVIRONMENT=development ~/bin/localenv plackup -R lib,share bin/netdisco-web-fg
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|
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=head2 Authentication
|
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|
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Dancer includes (of course) good session management using cookies and a memory
|
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database. You should change this to a disk database if using a proper forking
|
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web server installation so that sessions are available to all instances.
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|
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Session and authentication code lives in L<App::Netdisco::Web::AuthN>. It is
|
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fully backwards compatible with the existing Netdisco user management, making
|
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use of the database users and their MD5 passwords.
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|
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There is also support for unauthenticated access to the web app (for instance
|
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if you have some kind of external authentication, or simply trust everyone).
|
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=head2 Templates
|
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|
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In the C<share/views> folder of this distribution you'll find all the
|
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Template::Toolkit template files, with C<.tt> extensions. Dancer first loads
|
||||
C<share/views/layouts/main.tt> which is the main page wrapper, that has the HTML
|
||||
header and so on. It then loads other templates for sections of the page body.
|
||||
This is a typical Template::Toolkit "wrapper" configuration, as noted by the
|
||||
C<[% content %]> call within C<main.tt> that loads the template you actually
|
||||
specified in your Dancer handler.
|
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|
||||
All templates (and Javascript and Stylesheets) are shipped in the
|
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L<App::Netdisco> distribution and located automatically by the application
|
||||
(using the environment variables which App::Netdisco set up). The user doesn't
|
||||
have to copy or install any files.
|
||||
|
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There's a template for the homepage called C<index.tt>, then separate
|
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templates for searching, displaying device details, and showing inventory.
|
||||
These are, pretty much, all that Netdisco ever does.
|
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|
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Each of these pages is designed in a deliberately similar way, with re-used
|
||||
features. They each can have a "sidebar" with a search form (or additional
|
||||
search parameters). They also can have a tabbed interface for sub-topics.
|
||||
|
||||
Here's where it gets interesting. Up till now the page content has been your
|
||||
typical synchronous page load (a single page comprised of many templates) in
|
||||
response to a GET request. However the content of the tabs is not within this.
|
||||
Each tab has its content dynamically retrieved via an AJAX request back to the
|
||||
web application. Javscript triggers this automatically on page load.
|
||||
|
||||
This feature allows the user to search and search again, each time refreshing
|
||||
the data they see in the tab but without reloading the complete page with all
|
||||
its static furniture. AJAX can, of course, return any MIME type, not only JSON
|
||||
but also HTML content as in this case. The templates for the tabs are
|
||||
organised below C<share/views/ajax/...> in the distribution.
|
||||
|
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=head2 Stylesheets
|
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|
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The main style for Netdisco uses Twitter Bootstrap, which is a modern library
|
||||
of CSS and javascript used on many websites. It does a lot of heavy lifting,
|
||||
providing simple CSS classes for all of the standard web page furniture
|
||||
(forms, tables, etc). Check out the documetation at the Twitter Bootstrap web
|
||||
site for more information.
|
||||
|
||||
These stylesheets are of course customised with our own C<netdisco.css>. We
|
||||
try to name all CSS classes with a prefix "C<nd_>" so as to be distinct from
|
||||
Twitter Bootstrap and any other active styles.
|
||||
|
||||
All stylesheets are located in the C<share/public/css> folder of the
|
||||
distribution and, like the templates, are automatically located and served by
|
||||
the Netdisco application. You can also choose to serve this content statically
|
||||
via Apache/etc for high traffic sites.
|
||||
|
||||
Although Twitter Bootstrap ships with its own set of icons, we use an
|
||||
alternative library called Fontawesome. This plugs in easily to Bootstrap and
|
||||
provides a wider range of scaleable vectored icons which are easy to use.
|
||||
|
||||
=head2 Javascript
|
||||
|
||||
Of course many parts of the Netdisco site use Javascript, beginning with
|
||||
retrieving the page tab content itself. The standard library in use is jQuery,
|
||||
and the latest version is shipped with this distribution.
|
||||
|
||||
Many parts of the Netdisco site have small Javscript routines. The code for
|
||||
these, using jQuery as mentioned, lives in two places. The main C<netdisco.js>
|
||||
file is loaded once in the page HTML header, and lives in
|
||||
C<share/public/javascripts/netdisco.js>. There's also a
|
||||
C<netdisco_portcontrol.js> which is included only if the current user has Port
|
||||
Control rights.
|
||||
|
||||
Netdisco also has Javascript routines specific to the device search or device
|
||||
details pages, and these files are located in C<share/views/js/...> because
|
||||
they're loaded within the page body by the templates. These files contain a
|
||||
function C<inner_view_processing> which is called each time AJAX delivers new
|
||||
content into a tab in the page (think of it like a callback, perhaps).
|
||||
|
||||
Also in the C<share/public/javascripts/...> folder are the other public
|
||||
libraries loaded by the Netdisco application:
|
||||
|
||||
The Toastr library is used for "Growl"-like notifications which appear in the
|
||||
corner of the web browser and then fade away. These notify the user of
|
||||
successful background job submission, and jos results.
|
||||
|
||||
The d3 library is a graphics toolkit used to display the NetMap feature. This
|
||||
works differently from the old Netdisco in that everything is generated
|
||||
on-the-fly using SQL queries (C<DeviceLinks> resultset) and this d3 library
|
||||
for rendering.
|
||||
|
||||
Finally Twitter Bootstrap also ships with a toolkit of helpful Javascript
|
||||
driven features such as the tooltips and collapsers.
|
||||
|
||||
|
||||
=head1 Job Daemon
|
||||
|
||||
The old Netdisco has a job control daemon which processes "port control"
|
||||
actions and also manual requests for device polling. The new Netdisco also has
|
||||
a daemon, although it is a true separate process and set of libraries from the
|
||||
web application. However, it still makes use of the Dancer configuration and
|
||||
database connection management features mentioned above.
|
||||
|
||||
The job daemon is backwards compatible with the old Netdisco database job
|
||||
requests table, although it doesn't yet log results in the same way. Most
|
||||
important, it cannot yet poll any devices for discovery or macsuck/arpnip,
|
||||
although that's next on the list!
|
||||
|
||||
All code for the job daemon lives under the L<App::Netdisco::Daemon> namespace
|
||||
and like the rest of Netdisco is broken down into manageable chunks.
|
||||
|
||||
=head2 Running the Job Daemon
|
||||
|
||||
Like the web application, the job daemon is fully self contained and runs via
|
||||
two simple scripts shipped with the distribution - one for foreground and one
|
||||
for background execution (see the user docs for instructions).
|
||||
|
||||
The C<netdisco-daemon> script uses L<Daemon::Control> to daemonize so you can
|
||||
fire-and-forget the Netdisco job daemon without much trouble at all. This
|
||||
script in turn calls C<netdisco-daemon-fg> which is the real application, that
|
||||
runs in the foreground if called on its own.
|
||||
|
||||
=head2 Daemon Engineering
|
||||
|
||||
The job daemon is based on the L<MCE> library, which handles the forking and
|
||||
management of child processes doing the actual work. This actually runs in the
|
||||
foreground unless wrapped with Daemon::Control, as mentioned above. MCE
|
||||
handles three flavours of "worker" for different tasks.
|
||||
|
||||
One goal that we had designing the daemon was that sites should be able to run
|
||||
many instances on different servers, with different processing capacities.
|
||||
This is both to take advantage of more processor capability, but also to deal
|
||||
with security zones where you might only be able to manage a subset of devices
|
||||
from certain locations. Netdisco has always coped well with this via its
|
||||
C<discover_*> and similar configuration, and the separate poller process.
|
||||
|
||||
So, the single Manager "worker" in the daemon is responsible for contacting
|
||||
the central Netdisco database and booking out jobs which it's able to service
|
||||
according to the local configuration settings. Jobs are "locked" in the
|
||||
central queue and then copied to a local job queue within the daemon.
|
||||
|
||||
Along with the Manager we start zero or more of two other types of worker.
|
||||
Some jobs such as port control are "interactive" and the user typically wants
|
||||
quick feedback on the results. Others such as polling are background tasks
|
||||
which can take more time and are less schedule sensitive. So as not to starve
|
||||
the "interactive" jobs of workers we have two types of worker.
|
||||
|
||||
The Interactive worker picks jobs from the local job queue relating to device
|
||||
and port reconfiguration only. It submits results directly back to the central
|
||||
Netdisco database.
|
||||
|
||||
The Poller worker (is not yet written!) and similarly picks job from the local
|
||||
queue, this time relating to device discovery and polling.
|
||||
|
||||
There is support in the daemon for the workers to pick more than one job at a
|
||||
time from the local queue, in case we decide this is worth doing. However the
|
||||
Manager won't ever book out more jobs from the central Netdisco job queue than
|
||||
it has workers available (so as not to hog jobs for itself against other
|
||||
daemons on other servers). The user is free to configure the number of
|
||||
Interactive and Poller workers in their C<config.yml> file (zero or more of
|
||||
each).
|
||||
|
||||
=head2 SNMP::Info
|
||||
|
||||
The daemon obviously needs to use L<SNMP::Info> for device control. All the
|
||||
code for this has been factored out into the L<App::Netdisco::Util> namespace.
|
||||
|
||||
The L<App::Netdisco::Util::Connect> package provides for the creation of
|
||||
SNMP::Info objects along with connection tests. So far, SNMPv3 is not
|
||||
supported. To enable trace logging of the SNMP::Info object simply set the
|
||||
C<INFO_TRACE> environment variable to a true value. The Connect library also
|
||||
provides routines to map interface and PoE IDs.
|
||||
|
||||
Configuration for SNMP::Info comes from the YAML files, of course. This means
|
||||
that our C<mibhome> and C<mibdirs> settings are now in YAML format. In
|
||||
particular, the C<mibdirs> list is a real list within the configuration.
|
||||
|
||||
Other libraries will be added to this namespace in due course, as we add more
|
||||
functionality to the Job Daemon.
|
||||
|
||||
=head2 DBIx::Class Layer
|
||||
|
||||
The local job queue for each Job Daemon is actually an SQLite database running
|
||||
in memory. This makes the queue management code a little more elegant. The
|
||||
schema for this is of course DBIx::Class using Dancer connection management,
|
||||
and lives in L<App::Netdisco::Daemon::DB>.
|
||||
|
||||
There is currently only one table, the port control job queue, in
|
||||
L<App::Netdisco::Daemon::DB::Result::Admin>. It's likely this name will change
|
||||
in the future.
|
||||
|
||||
=head1 Other Noteable Technology
|
||||
|
||||
=head2 C<local::lib>
|
||||
|
||||
This is the system used to install Netdisco and all its Perl dependencies into
|
||||
a folder independent of the system's Perl libraries. It means Netdisco can be
|
||||
self-contaned and at the same time relocated anywhere. The L<local::lib>
|
||||
module is responsible for re-setting Perl's environment to point at the new
|
||||
library.
|
||||
|
||||
=head2 C<App::cpanminus>
|
||||
|
||||
This is simply a sane replacement for the CPAN shell. Don't ever bother with
|
||||
the CPAN shell again, just use the L<cpanm> client which comes with this
|
||||
distribution. We install Netdisco using C<cpanm>.
|
||||
|
||||
=head2 C<App::local::lib::helper>
|
||||
|
||||
This is a companion to C<local::lib> which provides the C<localenv> script you
|
||||
see referenced in the documentation. It's run automatically by Netdisco to
|
||||
locate its C<local::lib> folder (that is, works around the bootstrapping
|
||||
problem where the shipped app doesn't know to where it is relocated). We can
|
||||
help things along by setting the C<NETDISCO_HOME> environment variable.
|
||||
|
||||
=head2 C<Try::Tiny>
|
||||
|
||||
A replacement for C<eval> which provides proper C<try/catch> semantics. You
|
||||
have to take a bit of care unfortunately over things like C<return> statements
|
||||
though. However it's a lot cleaner than C<eval> in many cases. See the
|
||||
L<documentation|Try::Tiny> for further details.
|
||||
|
||||
=head2 C<Role::Tiny>
|
||||
|
||||
Anyone familiar with the concept of an I<interface> from other programming
|
||||
languages might understand what a role is. It's class functionality, often
|
||||
also called a "trait", which is composed into a class at run-time. This module
|
||||
allows the Daemon workers to dynamically assume different roles according to
|
||||
configuration.
|
||||
|
||||
=cut
|
||||
Reference in New Issue
Block a user