Neutron/ServiceDirectoryStructure

This page describes possible source code tree structure for advanced services. Note that there could be 2 major approaches to writing service implementation of a certain kind:

• 1 generic plugin extended by drivers
• several separate plugins

1 generic plugin extended by drivers

The first proposed layout is for (1) which we're going to adopt for the loadbalancer service

/plugins
   /services
       /loadbalancer
           /agents
               /vendorA
                   vendorA_agent.py
               /vendorB
                   vendorB_agent.py
           /drivers
               /vendorA
                    plugin_driver.py (plugin-side driver, could contain additional DB logic)
                    device_driver.py (driver to access a device, usually utilized by corresponding agent)
           /db
                loadbalancer_db.py
          plugin.py (generic loadbalancer plugin based on loadbalancer_db.py and using plugin_drivers to allow vendor-specific architectures)

Note that currently loadbalancer directory is named agent_loadbalancer which points to a particular implementation.
To make it more generic, the following 2-step changes are proposed:

• Move loadbalancer_db.py out of quantum/db/loadbalancer/ to quantum/plugin/services/agent_loadbalancer/db/
  
• Rename agent_loadbalancer directory to loadbalancer. That would require changing many imports and also affects devstack hence it might be better to do it in separate step.
  

Options to consider:
1) move whole services tree up 1 level out of plugins

Several separate plugins

/plugins
   /services
       /vendorA_loadbalancer
           /agents
               vendorA_agent.py
           /drivers
               device_driver.py (driver to access a device, usually utilized by corresponding agent)
           /db
                vendorA_loadbalancer_db.py
           vendorA_plugin.py
       /vendorB_loadbalancer
           ...

Similar rules apply to unit test files, basically all service-related files are moved under tests/unit/services/service_category/

Final directory layout

Example of loadbalancer naming and layout:

 /db/
     /loadbalancer
          loadbalancer_db.py
 /common
     plugin_constants.py (service types, constants shared between core and service plugins)
 /services
     /loadbalancer
           /agents
               /vendorA
                   vendorA_agent.py
               /vendorB
                   vendorB_agent.py
           /drivers
               /vendorA
                    plugin_driver.py (plugin-side driver, could contain additional DB logic)
                    device_driver.py (driver to access a device, usually utilized by corresponding agent)
          plugin.py (generic loadbalancer plugin based on loadbalancer_db.py and using plugin_drivers to allow vendor-specific architectures)