andrew/disco
Archived
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Moving things out of the README into the wiki

Browse Source
This commit is contained in:
Andrew Kesterson
2012-08-19 08:06:23 -04:00
parent 91cb7a291b
commit 3c769a1e93
1 changed files with 8 additions and 207 deletions
Download Patch File Download Diff File Expand all files Collapse all files

215
README.md
View File

@@ -3,215 +3,16 @@ disco
Dead Simple COnfiguration management and continuous integration for linux like systems Dead Simple COnfiguration management and continuous integration for linux like systems
DISCO is just now beginning development. Expect what you find here to do irreparable damage DISCO uses simple, proven technologies to achieve the goal of configuration management.
to any system you run it on. I ONLY run disco on a throwaway VM at current.
Why disco? * rsync for data transfer from master to client
===== * bash for scripts and templating
* unionfs and restricted bash for noop operations
* plaintext files in a structured directory tree for node classification and configuration
Because puppet, chef, cfengine, etc, are all great tools, but they all fall DISCO is in the very early alpha stages of development. At this point, I am fairly confident
short of the mark, in terms of simplicity, ease of use, and reliability. that it won't destroy the system you run it on, but I still only run it on disposable virtual
None of them really follow the UNIX philosophy of "do one thing, do it well, machines until it reaches a higher level of maturity.
and don't reinvent the wheel".
No, really, why did you name it "disco"?
=====
I wanted an acronym based off of "Dead Simple Continuous Integration", and this was
the closest I found.
Requirements
=====
DISCO assumes that you:
- have at least one server capable of running rsyncd, sshd and a recent GNU
- have one or more clients capable of running ssh, rsync, fuse-unionfs, and recent GNU
While that's a very simple requirements list, it currently restricts it to recent Linux
systems. You may or may not be able to use this tool on FreeBSD or Mac OS X, I haven't
tried. Due to the way it executes, this tool will probably never, ever execute properly
on Windows.
Installing DISCO
=====
1. Check out the sources
2. sudo make install
Why focus so much on linux?
=====
Because if we try to do everything and the kitchen sink, for every OS out there, we run
the risk of falling short in the same ways the other CI tools have. By limiting our scope
and problem space to recent GNU/Linux systems, we can write a much simpler tool in a
much shorter amount of time that is much simpler to understand.
Is DISCO noop friendly (report all incoming changes)?
=====
Yes, DISCO is noop friendly, with a caveat: The way we implement noop is through restricted bash
shells. This is generally sufficient, and already proven and simple.
There are some questions around "is the NOOP really secure then?" Well, yes and no.
The disco NOOP, like any (bash --restricted) shell, can be broken out of without a whole lot of work.
Especially considering that the restricted shell runs as root. In this case, the disco NOOP,
much like a barbed wire fence at a buffalo farm, is not expected to ACTUALLY keep anyone inside -
it's just a gentle suggestion that you please not run all over the farm breaking things.
Unlike puppet's noop, which is implemented via a guaranteed safe DSL, DISCO assumes an
existing trust network between your disco server and disco client; the goal of DISCO noop is to
prevent well-meaning trusted sysadmins from accidentally doing stupid things. It does not try
to secure your systems from malicious code. That security layer is moved up, onto the maintainer,
who must verify the sanity of all code they are sending to client machines.
Specifically: Since DISCO use a unionfs and chroot for the restricted bash shell, I am confiden
that your physical disk is safe from accidental modifications (everything is captured on the
scratchpad, with the exception of writes to /proc and /sys, which are read-only and simply discarded).
The bit that I can't promise is that one of your module maintainers won't find a way to kill a
running process, or signal/restart a service in a way that DISCO can't trap/log/noop it.
This may or may not be a big deal to you, but should be a consideration before you start
migrating to DISCO - how much do you trust your module maintainers?
How do you establish the trust relationship?
=====
DISCO uses rsync(+ssh) with SSH keys, so the answer is, "we don't establish it" - SSH handles
that for us by the server allowing or denying the key.
How do you handle parameters (like puppet ENC, etc)?
=====
DISCO uses a section of the filesystem to layout a tree of pathable, walkable parameters.
This part of the filesystem is available to the client at execution time, so these variables
can be used in scripts, templates, and definition files, to further customize execution based
off of parameters. This lives on the SERVER, not the client.
From the server perspective, the parameters tree looks like:
/var/disco/parameters
___ ___ disco
___ ___ ___ client
___ ___ ___ ___ cmds
___ ___ ___ ___ ___ rsync
___ ___ disco
___ ___ ___ server
___ ___ ___ ___ uri
___ ___ NODE_NAME
___ ___ ___ modules
___ ___ ___ ___ ...
___ ___ ___ parameters
___ ___ ___ ___ ...
Think of it like a large JSON document expressed as a filesystem, with the document keys the
filenames, and the values being their contents. This format was chosen because it can be easily
created from any number of other existing datasources, and doesn't tie DISCO to any one particular
tool (cobbler, etc). The admin is free to create this structure on the server however they please.
Given this, disco does not use a config file, all configuration parameters are present in this
tree.
There are only two possible toplevel paths, /disco and /NODE_NAME. NODE_NAME is equal to the
FQDN of the client making a request, and /disco is the internal client/server configuration.
The parameter tree is transmitted from the server to the client via (yet another) rsync
operation, and is accessible as a filesystem tree (or the disco-param command which is just a
bash wrapper). These parameters appear in /var/disco/parameters on the client and server, and
default values can be found there in the client/server install before the first run of the client.
disco/client/cmds/rsync : The rsync command to use when synching
files.
disco/server/uri : The rsync URI from which to fetch module definitions.
disco/NODE_NAME/modules : This list defines the modules to install
on a given node.
disco/NODE_NAME/parameters : This tree defines all configuration
parameters for the node not related to any module in particular.
Some special parameters are provided to the client, that do not exist on the paramters tree until
runtime:
disco/NODE_NAME/current_module : This parameter defines the full
name of the current module, such that a module definition file
can access its personal parameters via without knowing its name, e.g.:
$(disco-param get $(hostname)/classes/$(disco-param get $(hostname)/current_module)/some/module/specific/path)
How to deploy stuff
=====
DISCO uses rsync(+ssh) to distribute files, and bash to execute supporting scripts. It has a
rudimentary dependency mechanism implemented via a topological sort.
Essentially, to deploy something, you need 3 things:
- some static files on an rsync server
- some bash templates (scripts that output what their content should be) on an rsync server
- some scripts that may or may not do something with those files and templates
Scripts
=====
DISCO uses bash for a scripting and templating engine. Instead of writing a custom DSL that lets
you specify operations (like Puppet did) or utilize a higher level language (like Chef did with
ruby), DISCO just uses the proven bash shell.
Every time your module is executed (e.g. every time the disco client executes), all of the scripts
are executed. The order of execution is determined by alphabetically sorting the filenames, rc.d
style; so naming your scripts as 00-fix_perms.sh, 10-correct_nodes.sh, etc, will cause them to be
executed in the proper order. This prevents you from having to create a separate file that describes
the execution order.
Files vs Templates
=====
Files and Templates are delivered exactly the same way - via rsync.
Files are static files who are delivered on to the disk, and no more operations are done to them.
They are delivered with the same permissions that they are given by the rsync repository.
Templates are bash scripts who are delivered on to the disk, and then they are executed, with their
file contents replaced by their output. Templates are subject to all the same restrictions as scripts
(be mindful of the constraints of $NOOP), and in addition, they are ALWAYS interpolated in the safe
NOOP execution environment (file modifications will be discarded, and only rudimentary bash builtins
are enabled). Templates have access to all client parameters via the disco-param command. Templates
will end up with the same permissions that rsync gives them.
Module Layout
=====
A disco module (also called a "disco ball" for fun) looks like this:
MODULE
___ requires
___ parameters
├── files/
├── scripts/
└── templates/
Your module can theoretically pull files, scripts, and templates from any location that can be
reached via rsync; however, it is generally considerd good form to include all things relevant
to your module, inside its disco ball. The disco ball is then placed in an accessible location
on the rsync server, and the disco client will pull all modules, files, scripts, and templates
relevant to its execution, and run them.
ALL MODULE FILES, SCRIPTS, AND TEMPLATES ARE DELIVERED RELATIVE TO / ON THE CLIENT.
MODULE/requires
=====
This file lists, one name per line, the names of other modules that must be installed on this
node in order for this module to install correctly. This is used to create a dependency graph,
and thereby determine execution order.
This file is optional.
MODULE/parameters
=====
Each module can define default parameters which will be made available to all clients using the module.
These parameters will be merged together on the client at module fetch time, and any node-specific
parameters will override any default parameters specified here (they are rsync'ed over the top of each
other). These parameters will be rooted at /MODULE_NAME/... .
This tree is optional.
Server Side Setup Server Side Setup
===== =====