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V4/Integration Improvements

Name: V4/Integration Improvements
Target version: 4.5.0
Author: cheimes
Incomplete.png Pending review
Last updated: 2017-01-12 by Cheimes

Overview

Local installation and configuration of FreeIPA client libaries.

As of now it is rather hard to use FreeIPA's client API or command line programs outside of a regular, system-wide installation. FreeIPA doesn't follow best practices for Python packaging. It's a side effect if FreeIPA being a single vendor Open Source project.

  1. Despite the fact that the client libraries ipaclient and ipalib are written in Python and properly packaged with setuptools, FreeIPA client is not distributable and installable with pip. System-wide installation with a package manager is not an option for local installations inside a virtual env.
  2. FreeIPA assumes that the host has been enrolled by root with ipa-client-install. System-wide configuration as root is not an option for integrations. For instance for automation with Ansible it is preferable to have a local configuration that does not require host enrollment. The local of configuration files can be overriden already but FreeIPA lacks a simple and official API.
  3. The ipaplatform package contains platform and distribution specific configuration like service names, paths and constants. The package is configured on build time. It does not support runtime detection of platforms.

I'm proposing a series of small changes and improvements to FreeIPA's configuration and packaging in order to enable local installation and configuration of client-side tools. Once all improvements are in place, FreeIPA's client tools can be installed and configured in an isolated virtualenv. Multiple configurations and even different versions of FreeIPA's client libraries can be installed on a single machine. Admin privileges are only required to install compiler and some build dependencies, but not for virtualenvs and configuration.

Scope

The scope of the proposal is limited to Python client libraries. The Python packages and IPA_CONFDIR env var neither include FreeIPA server libraries (ipaserver, web interface, supporting daemons) nor enrolment of clients. A local installation just contains the Python code and the ipa command. First of all, the proposal will enable developers to use ipalib in 3rd party code to call FreeIPA plugins remotely over JSON or XML-RPC. For now, advanced features like keytabs and DNS auto-discovery are deliberately not included.

For now integration is limited to supported platforms: Fedora, RHEL and Debian-like platforms with systemd. Other platforms like Windows, BSD, macOS, and Linux distributions with System V Init are out of scope.

Example

Example:

# create and activate a virtual env
$ virtualenv /tmp/ipaenv
$ source /tmp/ipaenv/bin/activate

# install ipaclient and dependencies locally
(ipaenv) $ pip install ipaclient

# create and activate a local configuration
(ipaenv) $ ipa-client-gencfg /tmp/ipaenv/config master.ipa.example
(ipaenv) $ export IPA_CONFDIR=/tmp/ipaenv/config
(ipaenv) $ export KRB5_CONFIG=$IPA_CONFDIR/krb5.conf
(ipaenv) $ ls /tmp/ipaenv/config/
ca.crt  default.conf  krb5.conf  nssdb

# use local configuration to acquire TGT and talk to a server
(ipaenv) $ kinit admin
(ipaenv) $ ipa ping

The ipa-client-gencfg command is just an example.

Use Cases

  • As a developer of a third-party Python library or application I like to use ipalib to perform RPC plugin calls. I also like to follow common best practices for Python packages to install ipalib and its dependencies. These best practices pip install-able packages, virtual envs and tox.
  • As a developer of an OpenStack project I like to have a simple way to install and use FreeIPA client libraries on a variety of distributions.
  • As a developer of an OpenStack project unit and functional tests executed by tox in a venv are mandatory so the minimum is to be able to import ipalib/ipaplatform. The backend may be mocked or otherwise worked around but not being able to import code using IPA is a show-stopper.
  • As an ordinary user without root privileges I like to install and configure a local copy of the ipa command. I can acquire a Kerberos TGT and know the hostname of a FreeIPA server but can neiter install software with a package manager nor enroll my machine.
  • For an Ansible playbook I like to have a simple and consistent way to point ipa command and ipalib.api to a local FreeIPA config file krb5.conf and nssdb. The files can't be global and must be part of the current Ansible inventory.
  • As a maintainer of a project that uses ipaclient I like to verify compatibility with multiple versions of FreeIPA without resorting to heavy weight solutions like containers or virtual machines. Instead I prefer virtual envs with pinned package versions.

Lead Engineers

  • Christian Heimes (IPA/CS)

Supporting Engineers

  • Adam Young (OpenStack Platform)
  • Rob Crittenden (OpenStack Platform)

Design & Implementation

API for local configuration directory

At the moment FreeIPA has multuple ways to load a different config file than the default default.conf from /etc/ipa.

  • For ipa command, config options can be overriden with the -e flag. For example ipa -e confdir=/path/to/alternative/directory ping loads default.conf from an alternative directory.
  • Python application can override settings during the initialization phase of FreeIPA API, e.g. ipalib.api.bootstrap(confdir='/path/to/alternative/directory'). Once ipalib.api is fully configured, all settings are read-only.

Both approaches have some disadvantages. A user must repeat the -e option in every call to ipa or create a shell alias. It's both tedious and error-prone. Some scripts don't have an override, e.g. ipa-client-automount.

I propose a IPA_CONFDIR environment variable that works comparable with MIT Kerberos' KRB5_CONFIG environment variable, https://web.mit.edu/kerberos/krb5-1.14/doc/admin/env_variables.html . In presence of the environment variable, FreeIPA API will use the value of the environment variable as path for confdir. An explicit -e option or api.bootstrap() argument takes precedence over the environment variable. Some contexts (e.g. server, installers, update) will still depend on global setting and system file. Therefore they won't support the env var and refuse to initialize the API.

Precedents

Pros

  • IPA_CONFDIR works similar to MIT KRB5's KRB5_CONFIG.
  • Local configuration for ipa command and ipalib becomes easy. A user or program just has to set the environment variables IPA_CONFDIR and KRB5_CONFIG to local configuration files. All API calls automatically pick up the right configuration in the current shell session.

Cons

  • It's yet another way to set the confdir option.

Tickets / PRs

Add package dependencies for distribution with pip

With FreeIPA's recent move to setuptools, the Python build system supports wheels. Wheels https://wheel.readthedocs.io/en/latest/ is the new and recommended packaging format for Python libraries. In order to make FreeIPA's client packages easily install-able with pip, the packages need to provide a list of install requirements. Setuptools include the requirements in the packages'. Pip downloads and install the requirements automatically.

Build and runtime requirements

FreeIPA no longer contains C extensions. It depends on a couple of packages with C extensions that require a compiler, libraries and headers at build time. Python packages with C code are cffi, cryptography, gssapi, pyldap/python-ldap, python-nss and lxml. FreeIPA also uses some external programs like openssl, kinit and certutil from nss-tools.

ipapython's dependencies on libxml, libxslt and lmxl could be dropped replacing lxml with Python stdlib's xml.etree package. The XML parser in the standard library is built on top of libexpat. xml.etree does not provide all features of lxml.etree. That's not a problem since FreeIPA uses only basic features and no advanced features like XSLT or complex XPath. FIXED ipaclient no longer imports lxml.

Fedora / RHEL

On Fedora and RHEL the runtime dependencies are provided by:

  • python-pip
  • keyutils
  • krb5-workstation
  • openssl
  • openldap-clients
  • nss-tools
  • libffi

Further more build time dependencies are:

  • python-wheel
  • gcc
  • krb5-devel
  • libffi-devel
  • nss-devel
  • openldap-devel
  • openssl-devel
Debian

Runtime dependencies:

  • python-pip
  • krb5-user
  • openssl
  • ldap-utils
  • libnss3-tools
  • libffi6
  • libxml2
  • libxslt1.1

Build dependencies:

  • python-dev
  • python-wheel
  • build-essential
  • pkg-config
  • libkrb5-dev
  • libffi-dev
  • libnss3-dev
  • libldap2-dev
  • libsasl2-dev
  • libssl-dev
  • libxml2-dev
  • libxslt1-dev

Pros

  • FreeIPA's client libraries become easy installable in a virtual env.

Cons

  • Package requirements from freeipa.spec are duplicated in setup.py files. It increases package maintenance slightly.

Remarks

python-nss does not support wheels yet, https://bugzilla.redhat.com/show_bug.cgi?id=1389739

Tickets / PRs

ipaplatform auto-configuration

The ipaplatform package is an abstraction layer for platform and distribution specific settings and services. The other FreeIPA packages use ipaplatform.constants, ipaplatform.paths, ipaplatform.services, and ipaplatform.tasks. Internally the modules are aliases, e.g. on Fedora ipaplatform.paths is an alias for ipaplatform.fedora.paths. As of now the aliases are implemented with symlinks. The symlinks are created at build time by autoconf. The approach is not compatible with Python wheels and pip. FreeIPA packages might be build on Fedora but installed on CentOS.

I'm proposing two changes:

  • Platform selection shall become an import time decision. The platform id is read from /etc/os-release. The file is available on all relevant platform. It also contains an ordered list of similar platforms. For example on CentOS the ID is centos and ID_LIKE are rhel and fedora in that order. Since ipaplatform does not provide a ipaplatform.centos sub-package, it will automatically select ipaplatform.rhel as platform provider for CentOS.
  • ipaplatform is turned into a namespace package. A namespace package allows third parties to provide external packages with platform definitions, e.g. a ipaplatform.debian package.

Pros

  • The platform reflects the actual platform that FreeIPA is running on.
  • The platform selector falls back to related platform identifiers.
  • Third parties can provide pip install-able platform modules.

Cons

  • The implementation becomes a bit more complicated.

Remarks

The __path__ trick is not compatible with namespace packages. ipaplatform.__init__ cannot contain any code.

pylint is not able to understand meta import hooks. An AstroidBuilder plugin for pylint turned out to be too fragile. My new implementation uses a facade module that is replaced with the actual module.

Tickets / PRs

ipaplatform Debian support

FreeIPA upstream does not include platform configuration for Debian-based distributions. In order to support development and deployment on other distributions, FreeIPA should include Timo Aalton's patch for ipaplatform.debian. There is demand for Debian support from OpenStack side.

Tickets / PRs

PyPI packages

details TBD

I have reservered four package names on PyPI:

  • ipaclient
  • ipalib
  • ipaplatform
  • ipapython

Further more I have registered four additional packages to prevent name squatting attacks. The ipa and freeipa packages just contain metadata (dependency on ipalib) and no code. The ipaserver and ipatests packages have no release at all.

  • ipaserver
  • ipatests
  • ipa
  • freeipa

Upgrade

Package dependencies must be synced between RPM spec and setup.py / ipasetup.py.

How to Use

TBW

Test Plan

TBW