Automate your sysadmin with adl

I used to work for a company that was in the business of deploying laptops running Linux into hospitals. We automated the installation of these laptops to such a degree that all we had to do build a new laptop was unwrap it, plug it into an ethernet network and turn it on. We used PXE boot and our own bespoke deployment system to achieve it. It even supported deploying automatic configuration updates over a mobile phone connection, while the laptops were in a different country.

It never seems to be worth going to the effort to setup a tool like cfengine or puppet when configuring a new desktop computer, a virtual server to run your blog, or a VPS for a small client who is keen to keep the budget down. But why should automation be expensive?

There's a little tool that I use when I want automation, but I need to do it on the cheap; adl. I think "adl" standards for "ADmin Log", but it's so long since I wrote it that I forget.

Installation

Download the latest version, then unpack the tarball and type:

$ sudo cp adl /usr/local/bin
$ sudo chmod +x /usr/local/bin/adl

Recording commands

You use adl like this:

$ sudo adl -C Installing mongrel and god
$ sudo adl apt-get install ruby1.8-dev -y
$ sudo adl gem install mongrel
$ sudo adl gem install god

adl runs each command for you, and records them in a log file if they execute successfully. The log looks something like this:

##
# 2008/01/14: Installing mongrel and god (graham)
##
apt-get install ruby1.8-dev -y
gem install mongrel
gem install god

Note the format of this log file; it is indistinguishable from a shell script. Yep, that's right — it's your replayable record of what you did to setup your computer. Documentation and automation in one. Nifty.

The -C option added a block comment. They come in handy when you're reading through the log a few months later to find out just how you configured something. Use a lowercase -c to add a one line comment without a date stamp.

Recording changes to files

A replayable log is no good to you if you only record half the changes. What happens when you make some changes to a config file? adl will keep track of changes to files too. Since we installed god above, we might want to configure log rotation. That means we need to create a new file. Don't use vi/nano/emacs/whatever here; use adl with the -e switch:

$ sudo adl -e /etc/logrotate.d/god

adl will open your editor of choice (set the EDITOR environment variable to choose; if it's not set it'll default to vi) so you can create/change the file, then save your file to disk. It will also append the changes to the log file, again in a replayable manner. Here's the log entry for our logrotate.d file:

cat <<'EOPATCH' > /etc/logrotate.d/god
/var/log/god.log {
    daily
    compress
    copytruncate
    missingok
    rotate 28
}
EOPATCH

The Unix heads amongst you will have noticed that the above snippet will overwrite any existing copy of the file. Worry not, adl knew the file didn't exist before hand. If we now make a one line change to that file, we get something slightly different written to the log:

patch /etc/logrotate.d/god <<'EOPATCH'
--- /etc/logrotate.d/god.orig   2008-04-05 10:02:05.000000000 +0000
+++ /etc/logrotate.d/god    2008-04-05 10:02:13.000000000 +0000
@@ -3,5 +3,5 @@
     compress
     copytruncate
     missingok
-    rotate 28
+    rotate 14
 }
EOPATCH

That's it in a nutshell. Can you think of a way to improve on this? Leave me a comment, or check out the source and play with it yourself.

Tips

• Add a block comment before you start a major task.
• Change the editor used to edit files by setting the EDITOR environment variable.
• Change the name of the log file used by adl by setting the RECLOG environment variable.
• Use adl to install itself, by copying the script to your freshly installed computer and then typing sh ./adl -e /usr/local/bin/adl. Then load the contents of the adl script into the editor and save it. Hey presto - it records it's own installation in the log file!
• Test how easy it is to rebuild your servers before you need them; setup a freshly installed virtual machine and try exectuing your logs.

Summary

Automated server administration on the cheap involves:

• Installing your operating system in the usual manner.
• Installing and using adl.
• Backing up your /root/LOG file.
• Rebuilding a freshly installed computer by typing sh LOG.