On Thu, Jun 05, 2014 at 10:09:54PM -0400, Dmitri Pal wrote:
Hello,
Over the time multiple tools have been developed and used to address
different use cases around SSSD configuration.
We now have:
1) SSSD that needs to read a configuration. It uses ding-libs libini_config
for that purpose.
libini_config was historically developed to read configuration from C
services like SSSD.
It is currently used by SSSD and GSS proxy
It is not capable of modifying and saving the configuration. To be fair it
is capable but the interfaces are not exposed at the high level API. It will
take some (couple days or so to close this gap).
2) SSSD also needed to create sssd.conf at the installation time. It is
ueasy to do it from Python this is why an SSSD config python script have
been created. It is good at modifying the configuration and setting specific
values at the beginning of the sssd.conf's life. It is not suited well (at
least yet) for long term maintenance of the configuration file. It is also
SSSD specific.
3) Over the time there were RFEs that suggested that sssd configuration
should be extensible or overwritable.
The following ticket cover that:
https://fedorahosted.org/sssd/ticket/2247
The design has been published here
https://fedorahosted.org/sssd/wiki/DesignDocs/ding-libs/INIConfigMerge
4) There is a desire to manage SSSD over OpenLMI a cockpit in an object
oriented way. To do that (following the standard LMI model) the following
layring has been suggested and implemented:
Consumer (OpenLMI/Cockpit) -> D-Bus interface -> ifp service (responder) ->
augeas c api
More details are here:
https://fedorahosted.org/sssd/wiki/DesignDocs/OpenLMIProvider
5) In the absence of the good configuration solution for the integration
purposes, i.e. to integrate applications running on top of the system with
SSSD as a short term solution a puppet-augeas based way of configuring
sssd.conf was introduced the other day. The main requirements are to be able
to modify existing configuration and more specifically change the values
that represent a list of values.
6) From the very beginning we were hoping that there would be a way to be
able to define the grammar of the configuration file and check it to be able
to diagnose the config files and prevent their corruption. The idea was to
add this capability to libini as it provides a set of nice convenience
capabilities in comparison to Augeas. Also Augeas until not long ago was not
included in some distors.
The list above presents a spectrum of use cases and solution to those use
cases.
The goal of this email is to try to enumerate the use cases and constraints
and understand how the solution for those use cases can be consolidated and
unified and where it makes sense todo and where not. It is a goal to define
a reasonable alignment between the technologies and provide a path forward
to a reusable and maintanable stack.
So we have the needs:
1) Read config files at run time from C (daemons and D-BUS provider)
2) Write config files from C (configuration interface over LMI)
3) Create and modify files at installation and upgade using some simple
mean/API which can be C, python or anything else
4) Be able to manage configuration files in a object oriented manner with or
without D-BUS running
5) Be able to augment the code file without touching it
6) Provide a way to validate the file
So I see the following layering
+------------------+
| High level tools |
+------------------+
|
\/
+---------------------------+
| Object oriented interface |
+---------------------------+
| |
\/ \/
+-----------------+ +------------------+
| D-BUS responder | | D-BUS shim layer |
+-----------------+ +------------------+
| --------------------|
| |
\/ \/
+-------+ +----------------+
| C API |<-------------| File validator |
+-------+ +----------------+
/\ \
| \ +--------------+
| -------------->| Config file |
| +--------------+
| /\
+----------------+ |
| SSSD/GSS proxy | |
+----------------+ |
|
+------------------+
| SSSD Coinfig API |
+------------------+
/\
|
+--------------+
| Simple tools |
+--------------+
I have a general comment first. I'm missing the security aspect a bit.
Where are the decisions made who is allowed to write which data to the
config file? Currently only root is allowed to write to the on disk
config file and I think we should keep it this way. So the "legacy" path
via the SSSD config API is safe. I think the final decision about who
can write what to the config file should be done in the C API e.g. based
on the grammar for validation. But is it possible to get trusted
information about the origin of the request through all the layers down
to the C-API? Or do we need some kind of authentication in the C-API?
bye,
Sumit
This layout shows three distinct paths towards config file:
1) Old python API and tools on top (does authconfig use this path?)
2) Top level D-BUS api and advanced object oriented tools
3) C API
We need to make several decisions at this point:
a) How much we enhance-update-improve existing python API instead of using
new D-BUS interface.
IMO we should leave python API alone for foreseeable future but any new
changes should go via the new D-BUS interface
b) How we make sure that the D-BUS interface is really usable. It is not
that light weight.
Would be nice to be able to have a shim layer for the cases like docker
where there might not be D-BUS or systemd. This however might not be a
problem for us to solve. It might be a generic problem for all LMI style
providers. A lot in D-BUS world is autogenerated so I suggest that we ask to
be able to generate a mini D-BUS interface that would go directly from the
interface to the logic implemented in responder. I do not know what is best.
But I think it is a discussion to have with D-BUS guys and should be more
general.
For now we can assume that D-BUS is there and docker use case will be solved
in some generic way.
c) If we assume D-BUS and systemd it really makes sense to separate the
responder in charge of configuration from other responders and make it
started on demand when there is a real call over the D-BUS to make a config
change. IMO this work for splitting ifp into data ifp and config ifp should
be filed as a ticket and done as a part of 1.13 release.
d) What is going to be the low level C library? We have two candidates
libini and augeas.
I definitely have a preference towards libini but this does not mean I am
right. I do not have a lot of time to maintain libini. I do not see a reason
to rip it out and replace with augeas yet. But I also do not see a reason
why we should rely on augeas. Right now IMO it would be more work to rip
libini and switch to augeas but over time if we do more and more augeas work
it might be much less. I feel people are more comfortable with augeas than
using libini and adding to it as they go. I do not know why but suspect it
is because augeas has appeal of a more commonly used tool/interface. It is
all about what we think is the right path. If we decide that augeas is the
way to go then we should not invest into enhancing libini and start building
our improvements in augeas or around augeas. If we think that libini is the
right path because it fill give us more features, flexibility and control
then let us make it so that I am not the only contributor to it and people
would not have problems throwing patches at it on as needed basis.
For me this is a very important decision. Right now I feel I am on hook to
continue investing my scares time into libini. I think I am holding people
back with this so I would rather come to terms and move forward whatever we
think is best for SSSD, GSS proxy and potential other daemons that need to
read and deal with config files.
Thoughts?
--
Thank you,
Dmitri Pal
Sr. Engineering Manager IdM portfolio
Red Hat, Inc.
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