Scripted Configuration
Writing tests is pivotal to building software. Perhaps it is reasonable to say that the habit of writing tests is what a programmer means by engineering. Other essential practices include everything you need to build a project, and certainly source control! Systems administration borrows many of the same concepts: write a configuration, run to verify, then commit to deploy. Just like software development, this workflow must have a tight feedback loop, where we make one change at a time while monitoring for success or failure.
Unfortunately we have been have been tricked into believing that systems orchestration is an advanced topic. This is for good reason: traditional configuration management systems are cumbersome to use in trivial cases, and complex tasks quickly become intractable. The following demonstrations show how rset(1) can be used to define and test systems configuration. Since it is a tool for staging and executing scripts, you are free to use your own programming skills to build an approach tailored to the target environment.
Demo: A New Configuration for a Home Network
This is the sequence of events:
| 0:06 | The routes file defines the directories containing configuration to stage and a list of pln(5) files to evaluate for this host |
| 0:20 |
The contents of a
pln
file are labels followed by tab-indented content. The default interpreter
is
/bin/sh
|
| 0:30 | Create configuration files |
| 0:50 |
The
dry-run flag
(-n)
will show which hosts and labels match
|
| 0:58 |
Execute on hosts matching an address. The default regular expression for
labels is
^[0-9a-z].
The built-in utilities
rinstall(1)
and
rsub(1)
are created locally so that they appear on the remote host
|
| 1:09 |
Subsequent commands will require elevated privileges since the ssh user is not
root
|
| 1:09 |
Specifying the label pattern to run, a subset of the scripts.
Since
rset
uses an SSH control master, there is very little performance penalty
for writing small script fragments
|
| 1:49 |
rinstall
returns exit code
0
if a file is installed or updated; this is used to conditionally
reconfigure networking
|
| 1:49 | Use the native tools already provided by the target OS to configure services |
Demo: Manage a PostgreSQL Installation
This is a moderately complex example of building a data-driven orchestration framework:
| 0:07 | Starting with two newly provisioned VMs. These are referenced by IP address, but hostnames would work as well |
| 0:15 |
Most of the code in this repository is written in
ruby
and it's behavior is driven by a
yaml
file which defines the parameters for each database server
|
| 0:37 | Configure the first database (master) |
| 1:00 |
The schema for this database
is located in
_sources
directory, which is useful for large files.
rinstall(1)
fetches this over HTTP, which is reachable through port forwarding
|
| 1:16 | Upgrading from PG 11 to 12 accomplished by changing the version and running the configuration again |
| 1:45 | Configure the second database (standby) |
| 2:23 |
Most of these scripts import common functionality from
hostmap.rb
|
| 2:28 | Each label contains logic for testing and establishing a consistent state on the remote system |
| 3:06 | The final step isn't configuration, just a convenient way to check on the replication status |