In the spirit of application, adding a rudimentary readme. (344aecb)

README.md

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	1	+# Notes on tool's architecture
	2	+
	3	+This is Rudimentary Configuration Management (RCM) tool and is super true to its name. Everything is under `RCM` module/namespace to differentiate with other gems/ruby classes on the system.
	4	+
	5	+Things are dependent on order of execution; especially if a resource is created by another one in the run. In our case, this is experienced for managing `/var/www/html/index.html` file as it is created by installation of `apache2`.
	6	+
	7	+## Target system configuration
	8	+
	9	+`apache2`, `php5` and `libapache2-mod-php5` are installed. Then default `/var/www/html/index.html` is deleted and `/var/www/html/index.php` is dropped in its place.
	10	+
	11	+## Structure
	12	+
	13	+The layout of the project is as simple as it can be. All objects are in `objects` folder, while all the functions that execute on those objects, or their collection are in respective file in `managers` folder. `task.rb` is the controller and also doubles up as configuration parser and validator via `whatchugot`, `parse_packages`, `parse_files` and `parse_services`. Config parsing can be moved to its own class, but it was left as it is for this task as I tend to go into a rabbit-hole... and I need to deliver a solution asap.
	14	+
	15	+### Configration and resources
	16	+
	17	+YAML parser is natively available in ruby core, and was chosen over JSON for its easier markup. There are only in 3 sections in `config.yaml` - `packages`, `files` and `services` - and they are processed in that order. Files needed by the program (`hello_world.php`) are in `resources` folder. Dependencies can be specified for services, with a condition that `path` for file and `name` for package need to appear in respective section. There is no way to specify dependency for package or file at this time.
	18	+
	19	+### Objects
	20	+
	21	+All objects are under `objects` folder. `rcm_file`, `rcm_project` and `rcm_service` provide abstraction of respective resource for RCM purposes. They hold everything needed to evaluate current vs desired state.
	22	+
	23	+### Managers
	24	+
	25	+All functions that can be performed on an object or their collection are held in `managers` folder. Some of the functions in respective classes can be moved to object itself... and this thought would buttress what I mentioned earlier about going into rabbit-hole :P.
	26	+
	27	+For file operations, I rely on `FileUtils` provided by ruby core, whereas I execute commands on systems for packages. Had I used Python, there was an API available to interact with package system. After all, apt is also a Python application.
	28	+
	29	+## How's the tool working
	30	+
	31	+`bootstrap.sh` ensures `ruby2.0` is installed.
	32	+
	33	+`task.rb` is the main file and contains `main`. `config_<env>.yaml` holds environment dependent configuration. If `ENVIRONMENT` is not set, `config.yaml` is loaded, otherwise program expects environment dependent configuration as mentioned above.
	34	+
	35	+Config file is loaded at startup and various checks done to make sure configuration is is correct... within the bounds of this task. For example, for file resource `desired_state` is checked to be one of available types; and it is made sure that `local_file` is readable _if_ state is set to present. If there are dependencies mentioned for a service, a pointer to the resource is held respectively in `depends_file` and `depends_package` in `::RCM::Package` object.
	36	+
	37	+State is maintained in 2 objects:
	38	+
	39	+1. `@wanted` holds the state as mentioned in `config.yaml` or `config_<env>.yaml`. It is populated in `parse_packages`, `parse_files` and `parse_services`.
	40	+2. `@got` holds the state of resources currently present on the system.
	41	+
	42	+I first get `get_current_state` of packages and `converge_packages` because in current configuration, there is a file that appears only upon installation of `apache2` package. I then `get_current_state` of files and `converge_files`. Finally `restart_services_if_needed`.
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