/ 
Config-Model-0.628
River stage two • 11 direct dependents • 11 total dependents
/ Config::Model::AutoRead

NAME

Config::Model::AutoRead - Load configuration node on demand

SYNOPSIS

# top level config file name matches instance name
$model->create_config_class 
(
 config_class_name => 'OneAutoReadConfigClass',

 read_config  => [ { backend => 'cds_file' , config_dir => '/etc/cfg_dir'},
                   { backend => 'custom' , # dir hardcoded in custom class
                     class => 'ProcessRead' 
                   }
                 ],
 # if omitted, write_config will be written using read_config specifications
 # write_config can be array of hash ref to write several syntaxes
 write_config => { backend => 'cds_file', config_dir => '/etc/cfg_dir' } ,


 element => ...
) ;

# config data will be written in /etc/my_config_dir/foo.cds
# according to the instance name
my $instance = $model->instance(instance_name => 'foo') ;

# use with Augeas
$model->create_config_class 
(
 config_class_name => 'OpenSsh::Sshd',

 # try Augeas and fall-back with custom method
 read_config  => [ { backend => 'augeas' , 
                     config_file => '/etc/ssh/sshd_config',
                     # declare "seq" Augeas elements 
                     lens_with_seq => [/AcceptEnv AllowGroups [etc]/],
                   },
                   { backend => 'custom' , # dir hardcoded in custom class
                     class => 'Config::Model::Sshd' 
                   }
                 ],
 # write_config will be written using read_config specifications


 element => ...
) ;

DESCRIPTION

This class provides a way to specify how to load or store configuration data within the model (instead of writing dedicated perl code).

With these specifications, all the configuration information are read during creation of a node.

This load/store can be done with:

  • Config dump string (cds) in a file. I.e. a string that describes the content of a configuration tree is loaded from or saved in a text file. See Config::Model::Dumper.

  • Ini files (written with Config::Tiny. See limitations in "Limitations depending on storage".

  • Perl data structure (perl) in a file. See Config::Model::DumpAsData for details on the data structure.

  • XML. Not yet implemented (ask the author if you're interested)

  • Any format when the user provides a dedicated class and function to read and load the configuration tree.

  • Data can be loaded or stored using RedHat's Augeas library.

After loading the data, the object registers itself to the instance. Then the user can call the write_back method on the instance (See Config::Model::Instance) to store all configuration informations back.

Built-in read write format

Currently, this class supports the following built-in formats:

cds_file

Config dump string. See Config::Model::Dumper.

ini_file

Ini files written by Config::Tiny.

augeas

Use Augeas library

Custom backend

Custom backend must be specified with a class name that will features the methods used to write and read the configuration files:

read_config  => [ { backend => 'custom' , class => 'MyRead' } ]

The MyRead class that you will provide must have the methods read and write. Then, MyRead::read will be called with there parameters:

(object => config_tree_root, root => 'filesystem root' ,
                             config_dir => 'config dir', )

You can choose to specify yourself the read and write methods:

read_config => { backend  => 'custom', 
                 class    => 'MyRead', 
                 function => 'my_read' 
               }

and

write_config => { backend  => 'custom', 
                  class    => 'MyRead', 
                  function => 'my_write' 
                }

Limitations depending on storage

Some storage system will limit the structure of the model you can map to the file.

Ini files limitation

Structure of the Config::Model must be very simple. Either:

  • A single class with hash of leaves elements.

  • 2 levels of classes. The top level has nodes elements. All other classes have only leaf elements.

Augeas backend limitation

The structure and element names of the Config::Model tree must match the structure defined in Augeas lenses.

Sometimes, the structure of a file loaded by Augeas starts directly with a list of items. For instance /etc/hosts structure starts with a list of lines that specify hosts and IP adresses. The set_in parameter specifies an element name in Config::Model root class that will hold the configuration data retrieved by Augeas.

Configuration class with auto read or auto write

read and write specification

A configuration class will be declared with optional read or write parameters:

read_config  => [ { backend => 'cds_file', config_dir => '/etc/my_cfg/' } , 
                  { backend => 'custom', class => 'Bar' },
                ],
write_config => { backend => 'cds_file', config_dir => '/etc/my_cfg/' },

The read backends will be tried in the specified order:

  • First the cds file whose name depend on the parameters used in model creation and instance creation: <model_config_dir>/<instance_name>.cds The syntax of the cds file is described in Config::Model::Dumper.

  • A call to Bar::read with these parameters:

    (object => config_tree_root, root => 'filesystem root', config_dir => '...')

When a read operation is successful, the remaining read methods will be skipped.

When necessary (or required by the user), all configuration informations are written back using all the write method passed.

In the example above, only a cds file is written. But, both custom format and cds file are tried for read. This is also an example of a graceful migration from a customized format to a cds format.

You can choose also to read and write only customized files:

read_config  => { backend => 'custom', class => 'Bar'},

Or to read and write only cds files :

read_config  => { backend => 'cds_file'} ,

You can also specify more paratmeters that must be passed to your custom class:

read_config  => { backend => 'custom', class => 'Bar', config_dir => '/etc/foo'},

To migrate from an old format to a new format:

read_config  => [ { backend => 'custom', class => 'OldFormat',  function => 'old_read'} ,
                  { backend => 'custom', class => 'NewFormat',  function => 'new_read'} 
                ],
write_config => [ { backend => 'custom', class => 'NewFormat' } ],

read write directory

By default, configurations files are read from the directory specified by config_dir parameter specified in the model. You may override the root directory for test.

Read and write with Augeas library

You can use Config::Augeas to read and write data back. This way, the structure and commments of the original configuration file will preserved.

To use Augeas as a backend, you must specify the following read_config parameters:

backend

Use augeas in this case.

save

Either backup or newfile. See "Constructor" in Config::Augeas for details.

config_file

Name of the config_file.

lens_with_seq

This one is tricky. When an Augeas lens use the seq keywords in a lens, a special type of list element is created (See http://augeas.net/docs/lenses.html for details on lenses). This special list element must be declared so that Config::Model can use the correct Augeas call to write this list values. lens_with_seq must be passed a list ref of all lens names that contains a seq statement.

For instance:

read_config  => [ { backend => 'augeas' , 
                    save   => 'backup',
                    config_file => '/etc/ssh/sshd_config',
                    # declare "seq" Augeas elements 
                    lens_with_seq => [/AcceptEnv AllowGroups/],
                  },
                ],

AUTHOR

Dominique Dumont, (ddumont at cpan dot org)

SEE ALSO

Config::Model, Config::Model::Instance, Config::Model::Node, Config::Model::Dumper, Config::Augeas