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FLA Configuration Management (FLACM) Design

This design reviews a method for automatically propagating configuration changes to servers via a multi-stage pull mechanism. This will allow changes to be made once in a central location and have the changes propagate at a known regular interval.

Design Team

  • Grier Johnson - Author
  • Chuck McIntyre - Concept


  • Functional Configuration Management
  • Saves Time
  • Minimizes Admin Intervention on Failure
  • Modular Design that is Language Agnostic
  • OS Neutral
  • Easy to Manage Backend
  • Role/Class Based Controls
  • Ability to Initiate Configuration Retrieval
  • Passive Configuration Server
  • Host Specific Controls/Overrides
  • Trackable and Reversible Changes
  • Check-in Monitoring/Alerting


  • Functional Configuration Management - A system that provides Functional Configuration Management is a system that allows for changes to be made in as few places as possible with as little work as possible. Ideally with the system would allow an admin to never have to log into a remote host to make configuration changes.
  • Save Time - Save Time means just that, if something saves time it should take less time to do it the time saving way then to do it any other way. Ideally it should be MUCH faster to do it the time saving way.
  • Minimize Admin Intervention - Something that minimizes admin failure means that an admin should have to do only those jobs that absolutely require a human to do them. For example if a problem can be fixed by restarting a process, the system should restart the process on its own.
  • Modular - A system that is modular means that each piece knows what to send to another piece and what it should receive from another piece but it shouldn't be tied to that piece by language, OS, or anything other then a standardized protocol or API.
  • Language Agnostic - A system that is Language Agnostic means that each piece of the system could be written in an entirely different language assuming the language can functionally perform as that part of the system. See: Modular
  • OS Agnostic - The system should run on any system or at least as wide a range of systems as possible. For the scope of this design we're concentrating on Unix and Unix-like OSes.
  • Role Based Controls - Role Based Controls mean the system should support arbitrary roles assigned to servers. Roles should be able to be added at any given time to the configuration data source without change to the configuration management scripts.
  • Initiation of Configuration Retrieval - This just means that the system should have some method of allowing an admin to force the box to restart it's configuration process and pull the newest binaries/scripts. This, by it's nature, should be an automated process that effects as many servers as necessary with one command or one iteration of a series of commands.
  • Passive Configuration Server - A system with a passive server means that clients are not dependent on the server. They should gracefully handle the central server not being available.
  • Host Overrides - A system with host overrides means an individual host can be configured differently then all other hosts even though it may belong to a role. Host overrides can and should be limited to one-off configurations and should work with role, domain, and OS configurations whenever possible.
  • Trackable Change - A system with trackable changes means there should be some sort of way of seeing what changes were added and when.
  • Reversible Changes - A system with reversible changes should allow for new changes to be rolled back to historical old changes. See: Trackable Changes.
  • Check-in Alerting - A system with Check-In Alerting keeps track of the clients that have checked in and if those clients stop checking in for a period longer then a configurable threshold, it should alert in some manner. Check-in alerting must have some method to disable alerting for a host that has been decommissioned or will not be checking in for an extended period of time.


Currently there is no configuration management to speak of for our production data center. Simple things like changing the root password would require an admin to touch dozens of servers and manually type "passwd root" on each one. The same thing applies for local accounts, service configuration, software repositories, etc.

Along with the vast amounts of time required to make changes in this fashion manual changes open up the possibility of typos and servers that don't get updated. A production environment without this sort of configuration management requires and army of admins to make changes and clean up the mistakes made during those changes.


The only reasonable competitor in the configuration management space we could be expected to use would be cfengine. Unfortunately cfengine requires an admin team to learn a special "policy" language and limits configuration management to that policy language. What we hope to do with our configuration management is make a modular language that can accept plug-ins from any language from shell to C++ assuming they conform to the API.

So instead of making people become rigidly tied to a special language we want to make something that can adapt to the infrastructure environment instead of the other way around. The learning curve on a modular setup would be very low, as long as a person knew ONE scripting/programming language they'd be able to write customized plug-ins.

In addition to that FLACM will start simple and allow for more complicated actions to be performed on an as-needed basis. An admin team could get a useful level of functionality out of a base FLACM install by only using flat files with no scripting.

Design Detail

The configuration management software will be a multiphase setup that takes inspiration from computer boot strapping. Each phase will get progressively more complicated until the system runs out of phases. The basic flow of the configuration management software looks like this:

Bootstrap Flow

The details of this design can be broken into discussing the different phases of the configuration management itself and the toolkit that will be provided with FLACM to help deal with things like the bootstrap script deployment and FLACM log monitoring.

Bootstrap Phase

The bootstrap script is necessarily simple. The bootstrap code is written in Bourne shell for maximum compatibility. It will run from init (when available, in cron elsewhere) and kick off a while loop that attempts to download the OS Initialization script from a hard-coded location. Upon failure the while loop tries again. Upon success the OS Initialization phase is run with exec.



while (true)
  # Linux and New Solaris
  if [ -e /usr/bin/wget || -e /usr/sfw/bin/wget ]
    if [ ! -e /space/flacm ]
      mkdir -p /space/flacm
    elsif [ ! -d /space/flacm ]
      rm -rf /space/flacm
      mkdir -p /space/flacm
    cd /space/flacm
    wget http://url/to/script
  if [ $? != 0 ]
    exec /space/flacm/script
    sleep 300

Phase 1 - OS Initialization Phase

The bootstrap code executes the "Phase 1" script which gathers a limited amount of OS data and uses that to determine where to grab either the Environmental Initialization (Phase 2) script or the Configuration/Execution (Phase 3) script.

The Phase 1 script contains error checking, unlike or bootstrap code, so that if things fail we can restart the bootstrap and start over. Phase 1 must complete successfully for anything to work, so the accuracy of the error checking is vital here. Phase 1 failing should put a lot of verbose logs into /var/log/flacm/phase1.log if it can so the FLACM Log Checker (see Toolkit) can parse what's going on without an admin having to log into the box.

There are a variety of checks that can be run in Phase 1 determine the base OS. FLACM will initially parse /etc/redhat-release since the code will be written primarily for CentOS servers. FLACM should not be checking patch revisions at this point. That sort of granularity is pushed back into the Phase 2 script which gathers extended environment information.

Once the base OS is determined FLACM should either know how to find a data source that tells it where to get the Phase 2 or Phase 3 script. For the scope of the initial design the location is hard coded into the script with some basic variable swapping to account for different OSes. FLACM then downloads the script and runs it with exec.

Phase 2 - Environment Initialization Script

Phase 2 is optional in the work flow for FLACM, but can be useful for widely diverse environments that have many different OSes or OSes at a wide range of patch/revision levels.

Phase 2 is a phase for using OS specific tools to gather as large amounts of OS specific data to either feed to Phase 3 or to be used by Phase 2 to accurately point to the correct Phase 3 repository.

Examples of where this would be useful would be OSes that have long support lives, like Solaris, but more-or-less manual patching regimes, like Solaris. Of 30 systems that run Solaris 9 there might be radically different configurations as some systems are running a version of Solaris 9 from 2003 and others are patched all the way to 2006. New directives may have been added to configuration files in that time or old defunct ones may have been taken away.

Due to these possible oddities FLACM uses a separate Phase 2 so that this added complexity can be forgotten all together if an environment doesn't warrant it. Conversely it can be made much more robust if the environment does warrant it.

Phase 3 - Configuration and Execution phase

Phase 3 is, necessarily, the most complicated portion of FLACM since the core functionality resides in this phase.

Phase 3 does a number of tasks. The first thing it needs to do is determine the Domain and Roles of a system. The domain is the environment a server is in, such as QA, Production, Development, etc. The role is the function of the server such as LDAP, DNS, Web, etc. These two aspects along with the OS should define 95% of an environments configuration changes. The other 5% (or less) should be host specific changes.

The domain and roles can be derived from a number of sources. The first revision of this project will hold the Roles in a YAML file and the domain will be derived from the FQDN. A roles file might look like:

# Roles
  - raptor
  - blackbird 
  - panzer
  - awol
  - predator
  - raptor
  - predator

A server may have multiple roles, but admins need to be cautious of conflicts in configuration among roles. Once the phase 3 script has the OS, Domain, Role and Host information it downloads the necessary configuration files and scripts from the central repository. The data structure is flat files in a directory hierarchy. An example can be seen below things and

Phase 3 - Data Source Layout

/flacm/OS/{OS Name}/{OS Version}/root/etc
/flacm/DOMAIN/{Domain Name}/root/etc
/flacm/ROLES/{Role Name}/root/etc

Each section has it's own subdirectory under the flacm root. There can be other more specific subdirectories under that. Once the specific subdirectories have been traversed there should be two common directories "root" and "scripts". The "root" directory holds configuration files as they would appear on the file system of the server. For example, an /etc/password for all CentOS 4.2 servers would be placed in /flacm/OS/CentOS/4.2/root/etc/passwd. Actually the file would need to be named passwd.whole or passwd.part, these distinctions are examined in Phase 3 - File Extensions.

The scripts directory holds a number of specifically named scripts that are kicked off at particular times during the configuration process. These scripts are examined in Phase 3 - Scripts.

Phase 3 - File extensions

In order to allow for limited scripting, files placed into configuration management must have one of two file extensions. Files that are the whole configuration file, in that they should completely replace what's already on the system end with a .whole. Files that should be appended to and existing file should end with .part.

A practical example of this would be to have an OS level /etc/sudoers.whole file that replaced the sudoers file on every box of that OS level with a sudoers that gave access to root and the wheel group (or OS equivalent). Then the DOMAIN level would append access (sudoers.part) for the admins of that domain. The ROLES level would then add access for the operators of each of those roles with another sudoers.part. Finally, if the system hosted some sort of one-off script the HOST level would add sudo access for an operator to run that one-off script just for that host.

If a directory contains a {file}.whole AND and {file}.part only the {file}.whole will be used and a message to /var/log/flacm/phase3.log will be recorded.

Phase 3 - Scripts

Additionally each FLACM subsection contains a "scripts" folder. There are 3 acceptable scripts for each section except roles, which has 5. The three main scripts are:

/flacm/.../scripts/pre /flacm/.../scripts/fix /flacm/.../scripts/post The "pre" script is run after the files are downloaded locally but before any files are copied anywhere else. The pre script is where FLACM should be used to install RPM dependencies (from a repository, not FLACM) and basically get the server ready to take the configuration that will be put in place.

The "fix" script is immediately after the pre script. The "fix" script creates a false root, copies all the files over to it and chroots into that directory (for example it might run chroot /falseroot/OS/CentOS/4.2/ after copying the files from /flacm/OS/CentOS/4.2/ to that directory. This is the right place to modify permissions. The point behind this is that many data sources will flatten the permissions on a file to a single user and group and potentially even a single read/write permission setup. Creating a false root allows permissions to be set up first and then copy the files over.

The "post" script is run after all files are copied over to the appropriate places. This script should clean up any temporary files that FLACM created and integrate any new configuration files (like running "newaliases").

The roles section has two more scripts:

/flacm/.../scripts/install /flacm/.../scripts/uninstall Roles are the most dynamic property of a server. A server that is an LDAP server will more regularly become a non-LDAP server then it will move out of production or become a different OS. Because of this, the ability to remove a role is important. Also, roles are generally more complicated then other types of configuration and there is often tasks that need to be done once, but never again. For example if LDAP is installed the server no longer needs to point to an external LDAP server, but this only needs to be done once, so it doesn't belong in the "pre" script.

Each time a server figures out its roles it checks for /etc/flacm/roles.conf and checks to see if there are any new roles or removed roles. If there are new roles it runs the install script (after the fix script but before moving any config files). If there are any removed roles it runs the uninstall script from that role.

Phase 3 - Workflow

  1. Check for .ignore file, if present, do nothing, exit successfully
  2. Check for .reboot file, if present, download the new version and exec to it.
  3. Determine roles and domains
  4. Download OS, Domain, Roles, and Host configs and scripts from FLACM repository.
  5. Run OS pre
  6. Run OS fix
  7. scrub false root, remove any {file}.part if a {file}.whole exists
  8. copy whole files into place, append part files to existing configs
  9. Run OS post
  10. repeat previous 5 steps for Domain, Roles, Host
  11. During the Roles portion:
    • If there are any removed roles, run uninstall
    • If there are any new roles, run the pre, then fix, then install
  12. Check to see if Phase 3 is in cron, schedule if not
  13. Check to see if there is a /etc/flacm/.reboot file. Reboot if so.
  14. Check to see if the reboot time has been reached, Reboot if so.

Phase 3 - Misc Requirements

The phase 3 script should upgrade itself. On a regular basis it should check to see if there is a new version of the script and download it if there is. After a download it should run the new script immediately.

The phase 3 script should check to see if it's in cron. If it is not then it should schedule itself.

The phase 3 script should have a set time that it "reboots" or basically reruns the bootstrap program (in order to get the most current version). The code should also check for a /etc/flacm/.reboot file and reboot immediately if present.

Misc Requirements

Starting with Phase 1 all scripts should check for an /etc/flacm/.ignore file. If present the scripts do nothing. The logic behind this is that if the FLACM central server is down local changes need to be made, FLACM should not overwrite the changes when the server comes back up. This allows for an extended period of time to get a change put into FLACM.


The FLACM Toolkit is a collection of scripts that help make FLACM more effective. At the initial roll out there will be a script to help deploy the bootstrap script to remote machines.

Other scripts that will be written as time and resources allow are:

FLACM Log Checker - A tool to check the remote FLACM logs and return either raw data or an aggregated report.


This is not a YUM replacement! Do not store RPMs in FLACM.

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