Flavio Poletti > DotCloud-Environment > DotCloud::Environment

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Module Version: 0.9.4   Source  

NAME ^

DotCloud::Environment - easy handling of environment in dotcloud

VERSION ^

version 0.9.4

SYNOPSIS ^

   # Most typical usage, suppose you have a shared 'lib' directory
   # under the root of your dotCloud directory hierarchy
   use DotCloud::Environment 'path_for';
   use lib path_for('lib');
   use My::Shared::Module; # in your project-root/lib directory

   # Most typical usage when you set a default environment.json file
   # in the root of your project and you need to access the variables
   # of the 'redis' service
   use DotCloud::Environment 'dotvars';
   my $redis_vars = dotvars('redis');

   # Not-very-typical usage examples from now on!

   # get an object, fallback to $path if not in dotCloud deploy
   my $dcenv = DotCloud::Environment->new(fallback_file => $path);

   # you should now which services make part of your stack!
   my $nosqldb_conf = $dcenv->service('nosqldb');
   my $type = $nosqldb_conf->{type}; # e.g. mysql, redis, etc.
   my $vars = $nosqldb_conf->{vars}; # e.g. login, password, host...

   # suppose your nosqldb service is redis...
   require Redis;
   my $redis = Redis->new(server => "$vars->{host}:$vars->{port}");
   $redis->auth($vars->{password});

   # another service, similar approach
   my $conf = $dcenv->service('database');
   die 'not MySQL?!?' unless $conf->{type} eq 'mysql';

   my ($host, $port, $user, $pass)
      = @{$conf->{vars}}{qw< host port login password >}
   require DBI;
   my $dbh = DBI->connect("dbi:mysql:host=$host;port=$port;database=db",
      $user, $pass, {RaiseError => 1});

DESCRIPTION ^

DotCloud::Environment is useful when you design applications to be deployed in the dotCloud platform. It is assumed that you know what dotCloud is (anyway, see http://www.dotcloud.com/).

In general you will have multiple services in your application, and when you are in one instance inside dotCloud you can access the configuration of the relevant ones reading either /home/dotcloud/environment.yml or /home/dotcloud/environment.json. For example, this lets your frontend or backend applications know where the data services are, e.g. a Redis database or a MySQL one.

This modules serves to two main goals:

With respect to the second goal, it should be observed that most of the times in your development environment you don't have the same exact situation as in dotCloud, e.g. it's improbable that you have a /home/dotcloud directory around. With this module you can set a fallback to be used in different ways, e.g.:

A Note On Available Data

Data about DotCloud services is organized according to the structure of the variables set in the relevant files. There are four significant parts:

application

there can be multiple applications you're loading variables from, and DotCloud::Environment lets you distinguish them apart

service

this is the name of a service in DotCloud sense. For example, if you have application whatever like this:

   $ dotcloud list whatever
   whatever (flavor: legacy):
     - nosqldb (type: redis; instances: 1)       
     - sqldb   (type: mysql; instances: 1)       
     - www     (type: perl; instances: 1)        
     - backend (type: perl-worker; instances: 1)

you have four services defined: nosqldb, sqldb, www and backend

subservice

this represents a subgroup of variables in a service. You should always find two subservices: one is named ssh, the other one has the same name as the service type (e.g. redis, mysql,...).

It makes sense to consider ssh some kind of accessory information and the other subservice as the "real" service.

variable name

this is the name of the variable, which is associated to a subservice.

Values are assigned to variable names.

Suggested/Typical Usage

In order to keep your code clean, you will probably be dividing it depending on the functional block that will be deployed as a service in dotCloud. Suppose that you have a frontend service, a backend service and a database; you probably have the following directory layout:

   project
   +- dotcloud.yml
   +- backend
   |  | ...
   |  +- lib
   |     +- Backend.pm
   +- frontend
   |  | ...
   |  +- lib
   |     +- FrontEnd.pm
   +- lib
      +- Shared.pm

Each service is put into a separate directory and all the code that they both use (e.g. functions to connect to databases) is put in a common lib directory.

How should you use DotCloud::Environment?

The main goal is to let it find the right environment.json (or, equivalently, environment.yml) depending on the environment you are into. If you are in dotCloud there is actually no problem, because by default the right /home/dotcloud/environment.json file is selected; for your local development the best thing to do is to put the configuration file in the project's root directory, which becomes like this:

   project
   +- dotcloud.yml
   +- backend
   |  | ...
   |  +- lib
   |     +- Backend.pm
   +- frontend
   |  | ...
   |  +- lib
   |     +- FrontEnd.pm
   +- lib
   |  +- Shared.pm
   |
   +- environment.json

Putting the file in that position lets DotCloud::Environment find it by default when no /home/dotcloud/environment.json file (or the equivalent YAML file) is found in the system. Which hopefully is the case of your development environment.

In this case, you would have this in each service:

   # -- in BackEnd.pm and FrontEnd.pm --
   use DotCloud::Environment 'path_for';
   use lib path_for('lib');
   use Shared ...;

The function "path_for" helps you to set up the right path in @INC so that the module can find the shared code.

In the shared module you can do this:

   # -- in Shared.pm --
   use DotCloud::Environment 'dotenv';

   # ... when you need it...
   my $service = dotenv()->service('service-name');
   # ... now you have a hash ref which should have at least two
   # elements: ssh and the real subservice type, e.g. mysql, redis, ...
   my $redis_host = $service->{redis}{host};

Most of the time all you need is to access the variables related to a specific service, so there's a shortcut for this:

   use DotCloud::Environment 'dotvars';
   my %vars = dotvars('service-name');

The dotvars shortcut tries its best to DWIM, i.e. it lets you specify either the name of a service or the name of a subservice.

For example, suppose that you want to implement a function to connect to a Redis service called redisdb:

   sub get_redis {
      my %vars = dotvars('redisdb');
      # it could also be:
      #
      # my %vars = dotvars('redis'); # name of service type
      #
      # if there is only one service of type redis

      require Redis;
      my $redis = Redis->new(server => "$vars{host}:$vars{port}");
      $redis->auth($vars{password});
      return $redis;
   }

Of course you can use dotenv/dotvars directly in FrontEnd.pm and BackEnd.pm, but you will probably benefit from refactoring your common code to avoid duplications.

METHODS ^

new

   $dcenv = DotCloud::Environment->new(%params);
   $dcenv = DotCloud::Environment->new({%params});

Create a new object. Parameters are:

no_load

don't attempt to load the configuration

environment_string

unconditionally use the provided string, ignoring everything else;

environment_file

unconditionally use the provided file, ignoring everything else;

fallback_string

use the provided string if other methods fail;

fallback_file

use the provided file if other methods fail.

backtrack

if nothing works and no fallback is set, look for suitable files in filesystem. This option is activated by default, so you can use it to disable it (e.g. with backtrack => 0).

Unless no_load is passed and set to true, the object creation also calls the "load" method.

Returns the new object or croaks if errors occur.

load

   $dcenv->load(%params);
   $dcenv->load({%params});

Load the configuration for an application. The accepted parameters are environment_string, environment_file, fallback_string, fallback_file and backtrack with the same meaning as in the constructor (see "new").

The sequence to get the configuration string is the following:

environment_string

from parameter passed to the method

environment_file

from parameter passed to the method

environment_string

from parameter set in the constructor

environment_file

from parameter set in the constructor

DOTCLOUD_ENVIRONMENT_FILE

environment variable (i.e. $ENV{DOTCLOUD_ENVIRONMENT_FILE}). Note that this was formerly $ENV{DOTCLOUD_ENVIRONMENT} but due to DotCloud starting using this variable it is no longer available.

$DotCloud::Environment::main_file_path

which defaults to /home/dotcloud/environment.json (you SHOULD NOT change this variable unless you really know what you're doing)

fallback_string

from parameter passed to the method

fallback_file

from parameter passed to the method

fallback_string

from parameter set in the constructor

fallback_file

from parameter set in the constructor

If none of the above works there's still some hope in case there is option backtrack (or it was specified to the constructor). In this case, either file is searched recursively starting from the following directories:

Actually, option backtrack is enabled by default, so if you do not want the behaviour above you have to explicitly disable it (e.g. passing backtrack => 0 in the constructor).

It is possible to load multiple configuration files from multiple applications.

Returns a reference to the object itself.

as_json

   %json_for = $dcenv->as_json();
   $json_for = $dcenv->as_json();

Rebuild the JSON representations of all the applications.

Returns a hash (in list context) or an anonymous hash (in scalar context) with each application name pointing to the relevant JSON string.

as_yaml

   %yaml_for = $dcenv->as_yaml();
   $yaml_for = $dcenv->as_yaml();

Rebuild the YAML representations of all the applications.

Returns a hash (in list context) or an anonymous hash (in scalar context) with each application name pointing to the relevant YAML string.

merge_json

   $dcenv->merge_json($json_string);

Add (or replace) the configuration of an application, provided as JSON string. You should not need to do this explicitly, because this does the same for you with autodetection of the format:

   $dcenv->load(environment_string => $json_or_yaml_string);

Return a reference to the object itself.

merge_yaml

   $dcenv->merge_yaml($yaml_string);

Add (or replace) the configuration of an application, provided as YAML string. You should not need to do this explicitly, because this does the same for you with autodetection of the format:

   $dcenv->load(environment_string => $json_or_yaml_string);

application_names

   my @names = $dcenv->application_names();

Returns the names of the applications loaded. Generally only one application will be available, i.e. the one of the stack you're working with.

applications

   my %conf_for = $dcenv->applications();
   my $conf_for = $dcenv->applications();

Get a hash (in list context) or anonymous hash (in scalar context) with the relevant data of all the applications. Example:

   {
      app1 => {
         project      => 'app1',
         environment  => 'default',
         service_id   => 0,
         service_name => 'www',
         services     => {
            nosqldb => {
               redis => {
                  login    => 'redis',
                  password => 'wafadsfsdfdsfdas',
                  host     => 'data.app1.dotcloud.com',
                  port     => '12345',
               }
            }
            sqldb => {
               mysql => {
                  login    => 'mysql',
                  password => 'wafadsfsdfdsfdas',
                  host     => 'data.app1.dotcloud.com',
                  port     => '54321',
               }
            }
         }
      },
      app2 => {
         # ...
      }
   }

application

   my %conf_for = $dcenv->application($appname);
   my $conf_for = $dcenv->application($appname);

Get a hash (in list context) or anonymous hash (in scalar context) with the relevant data for the requested application. Example:

   {
      project      => 'app1',
      environment  => 'default',
      service_id   => 0,
      service_name => 'www',
      services     => {
         nosqldb => {
            redis => {
               login    => 'redis',
               password => 'wafadsfsdfdsfdas',
               host     => 'data.app1.dotcloud.com',
               port     => '12345',
            }
         }
         sqldb => {
            mysql => {
               login    => 'mysql',
               password => 'wafadsfsdfdsfdas',
               host     => 'data.app1.dotcloud.com',
               port     => '54321',
            }
         }
      }
   }

service

   my %conf_for = $dcenv->service(%params); # also with \%params
   my $conf_for = $dcenv->service(%params); # also with \%params

Get a hash (in list context) or anonymous hash (in scalar context) with the relevant data for the requested service. Example:

   {
      ssh => {
         host     => 'data.app1.dotcloud.com',
         port     => '12345',
         url      => 'ssh://data.app1.dotcloud.com:12345/',
      },
      redis => {
         login    => 'redis',
         password => 'wafadsfsdfdsfdas',
         host     => 'data.app1.dotcloud.com',
         port     => '12345',
      }
   }

The parameters are the following:

service

(Required) the name of the service.

application

(Optional) the name of the application.

The name of the application is optional because in most cases it can be omitted, e.g. because there is only one application. The name can be also provided in the service name, in line with what normally happens in dotCloud where the complete name of a service is something like application.service.

This is the algorithm:

If exactly one service is found it is returned, otherwise this method croaks.

subservice

   my %conf_for = $dcenv->subservice($subservice_name);
   my %conf_for = $dcenv->subservice(%params); # also with \%params
   my $conf_for = $dcenv->subservice(%params); # also with \%params

Get a hash (in list context) or anonymous hash (in scalar context) with the relevant data for the requested subservice. Example:

   redis => {
      login    => 'redis',
      password => 'wafadsfsdfdsfdas',
      host     => 'data.app1.dotcloud.com',
      port     => '12345',
   }

It can be called with a single non-reference scalar that represents the subservice to look for. Otherwise it accepts the following parameters in a hash or a reference to a hash:

subservice

the name of the subservice

service

the name of the service, see "service"

application

the name of the application, see "application"

with obvious meanings.

The application and the service name can also be specified in the subservice name with separating dots like in the following examples:

   application.service.subservice
   service.subservice

These configurations in the subservice name override parameters of the same name (e.g. specifying service.subservice overrides the $params{service} input parameters).

Croaks if more than one subservice with the given name is found.

subservice_vars

   my %vars   = $dcenv->subservice_vars('subservice-name');
   my $vars   = $dcenv->subservice_vars('subservice-name');
   my %vars   = $dcenv->subservice_vars(%params); # also \%params
   my $vars   = $dcenv->subservice_vars(%params); # also \%params
   my @values = $dcenv->subservice_vars(%params); # also \%params
   my $values = $dcenv->subservice_vars(%params); # also \%params

Shorthand to get the configuration variables of a single subservice.

The input parameter list can be a single string with the name of the subservice, or a hash/anonymous hash with parameters. Depending on the input, the return value might be structured like a hash or like an array:

subservice

the name of the subservice, see "subservice"

service

the name of the service, see "service"

application

the name of the application, see "application"

list

(Optional) if a list is provided, then the values corresponding to each item in order is returned. This allows writing things like this:

   my ($host, $port, $password) = $dcenv->service_list(
      service => 'nosqldb',
      list => [ qw< host port password > ],
   );

and get directly the values to put into variables. In this case, the return value can be a list of values or an anonymous array with the values.

If this parameter is not present, the whole name/value hash is returned, either as a list or as an anonymous hash depending on the context.

service_vars

   my %vars   = $dcenv->service_vars('service-name');
   my $vars   = $dcenv->service_vars('service-name');
   my %vars   = $dcenv->service_vars(%params); # also \%params
   my $vars   = $dcenv->service_vars(%params); # also \%params
   my @values = $dcenv->service_vars(%params); # also \%params
   my $values = $dcenv->service_vars(%params); # also \%params

Shorthand to get the configuration variables of a single service. This assumes that a main subservice can be found in the requested service, according to the following algorithm:

After this, the method behaves as if "subservice_vars" with the main subservice were called.

FUNCTIONS ^

Nothing is exported by default, but you can import the following functions. If you need both, you can use the :all tag, e.g.:

   use DotCloud::Environment ':all';

This module uses Sub::Exporter under the hood; this means that if you're not happy with the name of the imported subroutines you can provide your own names, e.g.:

   use DotCloud::Environment
      dotvars => { -as => 'dotcloud_variables_for' };
   my $vars = dotcloud_variables_for('my-service');

dotenv

   my $singleton = dotenv();

This function returns a default instance of DotCloud::Environment that should suit the needs for the typical/suggested usage. Subsequent calls to the function always return the same object.

It can be useful if you don't want a global variable in your code, e.g.:

   my @application_names = dotenv()->application_names();
   # ...
   my $vars = dotenv()->service_vars('my-sql-db');

dotvars

   my $vars = dotvars('service-name-or-subservice-name');

This function gets the configuration variables for the provided service using the default singleton instance. Most of the time this is exactly what you want, and nothing more.

This function actually calls "service_vars" or "subservice_vars" behind the scenes, you can pass all the parameters that the method accepts.

find_code_dir

   my $code_directory = find_code_dir(%params);

This function tries to find the file dotcloud.yml that describes the application backtracking from the current working directory and from the directory containing the file that called us (i.e. what happens to be (caller($n))[1]).

Parameters:

n

an integer, defaulting to 0, that tells how to call caller(). You shouldn't need to set it, anyway.

unix

when set, the name of the directory will be returned in Unix format, so that you can use it with use lib. By default the format is the same as the system.

This should be useful if you want to put a default configuration file there or if you want to set up a shared library directory. If you are interested into this feature, anyway, look at "path_for" which is easier to use.

path_for

   use lib path_for('lib');

This function produces a list of paths that are suitable for use lib. It uses "find_code_dir" internally, see it for details.

You should pass a list of subdirectories which will be rebased using the result of "find_code_dir" as a parent directory. If you are actually in the dotCloud enviroment, the example above produces the path /home/dotcloud/code/lib.

Returns a list of Unix paths, one element for each input directory.

AUTHOR ^

Flavio Poletti <polettix@cpan.org>

COPYRIGHT AND LICENSE ^

Copyright (C) 2011 by Flavio Poletti polettix@cpan.org.

This module is free software. You can redistribute it and/or modify it under the terms of the Artistic License 2.0.

This program is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose.

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