wiki:RefactorClient

Version 14 (modified by dclark, 15 years ago) (diff)

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Bcfg2 Client Code Refactoring

This branch is for work in decomposing the platform-specific client modules into service/packaging system-specific modules; the platform-specific modules will then just import the service/packaging system-specific modules they require (e.g. Redhat.py would import rpm.py and chkconfig.py, all the platforms will import encap.py, etc.)

A mailing list thread with more discussion of this is here:

Ticket #73 describes some aspects of this issue.

Desai's 4-Step Plan

  1. create a module Bcfg2.Client.Tool.BaseTool that defines an API for all tools (things like Bcfg2.Client.Tool.RPM and Bcfg2.Client.Tool.SMF, etc)
  2. build a set of error types that can be raised during tool instantiation and operation
  3. modify the Bcfg2.Client.Frame code to figure out what methods to call tools for entry verification, installation and removal.
  4. is things like schema updates and metadata code updates

Desai might try to hack up a baseline for the BaseTool class soon.

Implementation Status

This work is happening at:

https://svn.mcs.anl.gov/repos/bcfg/branches/refactor/client

Bcfg2.Client.Frame is nearly completely finished. (It mainly redirects calls to underlying tools.)

ToolStatusWho
RPMV/ / /RNLD
POSIXV/I/E/RNLD
EncapDC
APTNLD
SYSV
ChkConfig?CL
Update-RC.d
SMF
LaunchdTL
Emerge

(V == Verify/I == Install/E == Extra detection/R == Removal)

Design Notes

Bcfg2.Client.Frame redirects calls to underlying tools. Its methods are:

  • Inventory - Compare client state to configuration specification
  • Install - Install wrong entries (sparsely, if specified)
  • FindExtra - Locate extra entries using tool-specific heuristics
  • Query - get user input of which entries should be modified
  • Remove - remove specified extra entries

Tool methods:

  • Verify<entry.tag> - verify entry state. Must return True/False?
  • Install<entry.tag> - install entry. Must return True/False?
  • Install (optional) - bulk install method for entries
  • FindExtra - locate extra entries

Writing a Client Tool Module

  1. Add a new file in src/lib/Client/Tools/
  2. Add an entry for this file in src/lib/Client/Tools/init.py
  3. Add a class in this file, with the same name as the file, that subclasses Bcfg2.Client.Tools.Tool (Bcfg2.Client.Tools.PkgTool for packaging systems)
  4. Add a method Verify<entry.tag> that returns true or false, based on client state (Mark Verify as done)
  5. If Add a method Install<entry.tag> that returns true or false. (For non package tools)
  6. Add a Remove method that removes entries based on self.setup (Mark Removal as done)
  7. Add a FindExtra method that locates entries not included in the configuration (Mark Extra Detection as done) (optional; this may not be possible depending on the tool)

For packaging tools, subclass Bcfg2.Client.Tools.PkgTool and define pkgtype and pkgtool. See the RPM module for an example.