config databaseroles

DatabaseRoles

This optional configuration setting allows you to specify a file that defines additional database servers that can be used to distribute load for database requests. This would require you to configure multiple database servers, one as a 'master' and additional 'slave' servers that replicate the data from the master database server. The additional slave database servers can be used for handling read-only requests (SELECT queries).

To configure Melody to use additional servers, you start by specifying the 'DatabaseRoles' configuration setting.

Default

none

Values

The value for the setting is a file name for a YAML-formatted text file.

All config settings/directives where you specify a path or a path+filename are specified relative to the location of the config file itself (like a CSS file in that regard; where all url() references in a stylesheet file are relative to the location of the stylesheet file).

A full path can also be used of course.

Example

config.cgi

Database mtdb
DBUser melody
DBPassword nelson
DatabaseRoles path/relative/to/mt-config-file/DBRoles.yaml

DBRoles.yaml

global:
    user: default-readonly-username
    slaves:
        - host: read-only-slave1.example.com
          user: user-for-slave1
        - host: read-only-slave2.example.com
        - host: read-only-slave3.example.com

The 'global' heading identifies the 'global' role, which is the primary role for Melody database connections. Melody currently only supports a single master database, but will be offering support for multiple master databases in the future. So for now, 'global' is the only role supported. Under the role heading ("global:"), you may specify the following settings which will serve as the default values for any slave connections declared. The following values may be given:

• dbname - Database name (defaults to 'Database' from config file)
• user - Database username (defaults to 'DBUser' from config file)
• pass - Database password (defaults to 'DBPassword' from config file)
• host - Database hostname (defaults to 'DBHost' from config file)
• port - Database port number (defaults to 'DBPort' from config file)
• sock - Database socket (defaults to 'DBSocket' from config file)
• cycle - Limit to length of any persistent database connection (specified in minutes)

Under the "slaves:" heading, you provide the information necessary to make a connection to each slave you have configured. Each of the above settings may also be defined for each slave, if necessary. Values that are not specified for the slave configuration are drawn from the "global" settings instead.

More Examples

Single Slave DB.yaml

config.cgi

Database mtdb
DBUser melody
DBPassword nelson
DatabaseRoles SingleSlaveDB.yaml

SingleSlaveDB.yaml

global:
    host: dbrw-1.ai.com
    cycle: 60
    slaves:
        - host: dbro-1.ai.com

MultiReadOnlyDB.yaml

config.cgi

Database mtdb
DBUser melody
DBPassword nelson
DatabaseRoles MultiReadOnlyDB.yaml

MultiReadOnlyDB.yaml

global:
    cycle: 60
    host: dbrw-0.ai.com
    slaves:
        - host: dbro-1.ai.com
        - host: dbro-2.ai.com
        - host: dbro-3.ai.com

• Categories: Appendix: Configuration Directives
• Tags: config, database, database server, master, roles, server, slave, yaml