On language bindings & Relaunching Guile-GnuTLS

The Guile bindings for GnuTLS has been part of GnuTLS since spring 2007 when Ludovic Courtès contributed it after some initial discussion. I have been looking into getting back to do GnuTLS coding, and during a recent GnuTLS meeting one topic was Guile bindings. It seemed like a fairly self-contained project to pick up on. It is interesting to re-read the old thread when this work was included: some of the concerns brought up there now have track record to be evaluated on. My opinion that the cost of introducing a new project per language binding today is smaller than the cost of maintaining language bindings as part of the core project. I believe the cost/benefit ratio has changed during the past 15 years: introducing a new project used to come with a significant cost but this is no longer the case, as tooling and processes for packaging have improved. I have had similar experience with Java, C# and Emacs Lisp bindings for GNU Libidn as well, where maintaining them centralized slow down the pace of updates. Andreas Metzler pointed to a similar conclusion reached by Russ Allbery.

There are many ways to separate a project into two projects; just copying the files into a new git repository would have been the simplest and was my original plan. However Ludo’ mentioned git-filter-branch in an email, and the idea of keeping all git history for some of the relevant files seemed worth pursuing to me. I quickly found git-filter-repo which appears to be the recommend approach, and experimenting with it I found a way to filter out the GnuTLS repo into a small git repository that Guile-GnuTLS could be based on. The commands I used were the following, if you want to reproduce things.

$ git clone https://gitlab.com/gnutls/gnutls.git guile-gnutls
$ cd guile-gnutls/
$ git checkout f5dcbdb46df52458e3756193c2a23bf558a3ecfd
$ git-filter-repo --path guile/ --path m4/guile.m4 --path doc/gnutls-guile.texi --path doc/extract-guile-c-doc.scm --path doc/cha-copying.texi --path doc/fdl-1.3.texi

I debated with myself back and forth whether to include some files that would be named the same in the new repository but would share little to no similar lines, for example configure.ac, Makefile.am not to mention README and NEWS. Initially I thought it would be nice to preserve the history for all lines that went into the new project, but this is a subjective judgement call. What brought me over to a more minimal approach was that the contributor history and attribution would be quite strange for the new repository: Should Guile-GnuTLS attribute the work of the thousands of commits to configure.ac which had nothing to do with Guile? Should the people who wrote that be mentioned as contributor of Guile-GnuTLS? I think not.

The next step was to get a reasonable GitLab CI/CD pipeline up, to make sure the project builds on some free GNU/Linux distributions like Trisquel and PureOS as well as the usual non-free distributions like Debian and Fedora to have coverage of dpkg and rpm based distributions. I included builds on Alpine and ArchLinux as well, because they tend to trigger other portability issues. I wish there were GNU Guix docker images available for easy testing on that platform as well. The GitLab CI/CD rules for a project like this are fairly simple.

To get things out of the door, I tagged the result as v3.7.9 and published a GitLab release page for Guile-GnuTLS that includes OpenPGP-signed source tarballs manually uploaded built on my laptop. The URLs for these tarballs are not very pleasant to work with, and discovering new releases automatically appears unreliable, but I don’t know of a better approach.

To finish this project, I have proposed a GnuTLS merge request to remove all Guile-related parts from the GnuTLS core.

Doing some GnuTLS-related work again felt nice, it was quite some time ago so thank you for giving me this opportunity. Thoughts or comments? Happy hacking!

Cosmos – A Simple Configuration Management System

Back in early 2012 I had been helping with system administration of a number of Debian/Ubuntu-based machines, and the odd Solaris machine, for a couple of years at $DAYJOB. We had a combination of hand-written scripts, documentation notes that we cut’n’paste’d from during installation, and some locally maintained Debian packages for pulling in dependencies and providing some configuration files. As the number of people and machines involved grew, I realized that I wasn’t happy with how these machines were being administrated. If one of these machines would disappear in flames, it would take time (and more importantly, non-trivial manual labor) to get its services up and running again. I wanted a system that could automate the complete configuration of any Unix-like machine. It should require minimal human interaction. I wanted the configuration files to be version controlled. I wanted good security properties. I did not want to rely on a centralized server that would be a single point of failure. It had to be portable and be easy to get to work on new (and very old) platforms. It should be easy to modify a configuration file and get it deployed. I wanted it to be easy to start to use on an existing server. I wanted it to allow for incremental adoption. Surely this must exist, I thought.

During January 2012 I evaluated the existing configuration management systems around, like CFEngine, Chef, and Puppet. I don’t recall my reasons for rejecting each individual project, but needless to say I did not find what I was looking for. The reasons for rejecting the projects I looked at ranged from centralization concerns (single-point-of-failure central servers), bad security (no OpenPGP signing integration), to the feeling that the projects were too complex and hence fragile. I’m sure there were other reasons too.

In February I started going back to my original needs and tried to see if I could abstract something from the knowledge that was in all these notes, script snippets and local dpkg packages. I realized that the essence of what I wanted was one shell script per machine, OpenPGP signed, in a Git repository. I could check out that Git repository on every new machine that I wanted to configure, verify the OpenPGP signature of the shell script, and invoke the script. The script would do everything needed to get the machine up into an operational stage again, including package installation and configuration file changes. Since I would usually want to modify configuration files on a system even after its initial installation (hey not everyone is perfect), it was natural to extend this idea to a cron job that did ‘git pull’, verified the OpenPGP signature, and ran the script. The script would then have to be a bit more clever and not redo everything every time.

Since we had many machines, it was obvious that there would be huge code duplication between scripts. It felt natural to think of splitting up the shell script into a directory with many smaller shell scripts, and invoke each shell script in turn. Think of the /etc/init.d/ hierarchy and how it worked with System V initd. This would allow re-use of useful snippets across several machines. The next realization was that large parts of the shell script would be to create configuration files, such as /etc/network/interfaces. It would be easier to modify the content of those files if they were stored as files in a separate directory, an “overlay” stored in a sub-directory overlay/, and copied into the file system’s hierarchy with rsync. The final realization was that it made some sense to run one set of scripts before rsync’ing in the configuration files (to be able to install packages or set things up for the configuration files to make sense), and one set of scripts after the rsync (to perform tasks that require some package to be installed and configured). These set of scripts were called the “pre-tasks” and “post-tasks” respectively, and stored in sub-directories called pre-tasks.d/ and post-tasks.d/.

I started putting what would become Cosmos together during February 2012. Incidentally, I had been using etckeeper on our machines, and I had been reading its source code, and it greatly inspired the internal design of Cosmos. The git history shows well how the ideas evolved — even that Cosmos was initially called Eve but in retrospect I didn’t like the religious connotations — and there were a couple of rewrites on the way, but on the 28th of February I pushed out version 1.0. It was in total 778 lines of code, with at least 200 of those lines being the license boiler plate at the top of each file. Version 1.0 had a debian/ directory and I built the dpkg file and started to deploy on it some machines. There were a couple of small fixes in the next few days, but development stopped on March 5th 2012. We started to use Cosmos, and converted more and more machines to it, and I quickly also converted all of my home servers to use it. And even my laptops. It took until September 2014 to discover the first bug (the fix is a one-liner). Since then there haven’t been any real changes to the source code. It is in daily use today.

The README that comes with Cosmos gives a more hands-on approach on using it, which I hope will serve as a starting point if the above introduction sparked some interest. I hope to cover more about how to use Cosmos in a later blog post. Since Cosmos does so little on its own, to make sense of how to use it, you want to see a Git repository with machine models. If you want to see how the Git repository for my own machines looks you can see the sjd-cosmos repository. Don’t miss its README at the bottom. In particular, its global/ sub-directory contains some of the foundation, such as OpenPGP key trust handling.

Redmine on Debian Lenny Using Lighttpd

The GnuTLS trac installation is in a poor shape. To fix that, I looked into alternatives and found Redmine. Redmine appears to do most things that I liked in Trac (wiki, roadmap and issue tracking) plus it supports more than one project (would come in handy for my other projects) and has built-in git support. I would like to see better spam handling and OpenID support, but it is good enough for our purposes now, and there are similar concerns with trac.

However, getting it up and running with lighttpd on a modern debian lenny installation was not trivial, and I needed some help from (thanks stbuehler). After finally getting it up and running, I made a copy of the machine using rsync and rsnapshot, so I could re-create a working configuration if I get stuck, and then re-installed the virtual machine.

The notes below are the steps required to set up Redmine using Lighttpd and MySQL on a Debian Lenny. I’m posting this to help others searching for the error messages I got, and to help my own memory in case I need to re-install the server sometime.
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