How I maintain multiple rsyslog versions

Rsyslog is an enterprise-class project. Among others, this means we need to provide different versions for quite a while (enterprises don’t like to update every 6 month, and don’t do so for good reasons).

As such, we support multiple major versions. As of this writing, the versions used in practice are v5, v7 and v8 upcoming shortly. There are also v0,…,v4 versions out there, and what I write applys to them equally. If there is development going on for a version, there is a vX-devel branch. This is for those that want the new features, obviously at the expense of some enhanced chance for instability. And then there is vX-stable, which is the stable branch. Once something is named vX-stable, it NEVER receives new features, just bug fixes. There is one exception from the naming rules: the most current development version is held inside the git master branch — because that’s where people expect it. So, currently, there is no v8-devel branch, but it’s named “master” instead.

Maintaining multipl versions sounds scaring and cumbersome. Indeed, this fear came up when talking about maintaining multiple doc versions inside the rsyslog-doc project. Thanks to git, this is not the case. It’s actually dumb easy to do, once you get a little used to the workflow.

The key thing is to make changes in the oldest branch where they belong (with “oldest” being the one that the project really want’s to support). So if there is a bug that’s present in v7-stable, v7-devel and master, do NOT fix it in master. Checkout v7-stable and fix it there. The same applies to doc updates. Once you have fixed it, all you need to do is to merge the changes up. Especially for smaller changes, git does most of the hard plumbing. Occasionally, there may be some merge conflicts, but these can usually quickly solved. There are some rare exceptions, usually as the result of big refactoring. For doc, merge conflicts are always almot trivial to solve (at least have been in the past). It’s advisabile to merge up early. The longer you wait, the more work you need to do if a merge conflict occurs (because you probably don’t remember well enough what you did). The backdraw of that is that the git history becomes a little cluttered with merge entries, but that’s how it is (nothing in life is free ;)).

So in the workflow is as follows (I use the v7-stable as the “oldest” version in this workflow sample; that’s also the typical case):

  1. git checkout v7-stable
  2. update whatever you need to update
  3. git commit
  4. git checkout v7-devel
  5. git pull . v7-stable
  6. git checkout master
  7. git pull . v7-devel
  8. DONE

In esscence, you make the change once and take 30 seconds to merge it up. Merge conflicts happen seldom and are quite unlikely for doc changes. Those that happen are usually just additions to related areas, and so it takes another 30 seconds to fix them. All in all very painless.

If you check the git logs, you’ll often find occurences of the workflow above (just look for the merges, they really stand out).

Now there remains the question of multiple versions, not branches. For example, we have v7.4.0, 7.4.1, 7.4.2,… How do we handle updates to them. Well, easy: first of all when 7.4.x is out, 7.4.(x-1) is NEVER again change (why should it, that’s for the next version). So we actually do NOT do any updates to already released versions (again, think about the resulting mess). So it just boils down to being able to fetch the exact same version later. And this is extremely easy with git: just use a tag, that’s what this is meant for.

So whenever I do a release, the last thing I do after it is build and being announced is do a “git tag “, e.g. “git tag v7.4.7”. That way, I can later do “git checkout v7.4.7” and have exactly the version I look for. Note, though, that you need to do “git push –tags” in order to push the tags to your published repository.

Conclusion: using git branches and release tags makes it extremely easy to maintain a multitude of version. Without git, this would be an almost undoable task (we had a really hard time in those CVS days…).

Why is the rsyslog project running its own infrastructure?

Currently, there is a very valuable discussion going on on the rsyslog mailing list on how we can attract more contributors and how moving things to github can help with this. I was writing a longer reply, and then it occured to me that it probably is better to blog about this topic as it may be of future interest to have the current thinking (relatively) esay accessible.
The core question being asked is “Would it make more sense to leave all that sort of info in one place instead of pulling people from the *official* rsyslog repo on *github* over to **?” Then, it had some examples of how logstash uses github README files for that [full text here in the rsyslog mailing list archives].
These are my thoughts:
I don’t object placing a bit more into readme and related files. However, while this one of the official  repos*, it’s not the official *project site*, so I think it makes sense to ask people to go to the project site for anything that’s non-trivial. Looking at the logstash things, to me it pretty much looks like they do the same thing. I have absolutely no problem putting the same information into README-like files inside the repository, as long as the authorative pages reside on the official project web (and yesterday I have begun to do so).
In essence, the question boils down to “why don’t I want to be locked in into github?” It’s (bad) experience. When rsyslog started we used intensively. At that time, it was as popular and the place to be on” that github is today. Then, they got some crazy biz ideas, got technical and other problems and … it really turned out to be a mess and bad for the project.

Also, we used Freshmeat for most of our public announcements around the same time (a bit later, and partly togehter with All went extremely well, until out of the sudden they had the bright idea of a “redesign” that made the site unusable. Again, bad hit for us.

I really don’t want to see this again. If I use github exclusively, I have no chance to redirect things if they go crazy. I have a hard time moving on to the next hot spot when it is born (because all the Google juice is with github).
I admit that I would like to have the buzz of “I tell you this is an active project, I can judge by the number of issues opened and closed (and so on)”. But at the same time, I remember that this type of entanglement always turned against us after some time.
For example, I tend to file the bug number (actually a link to it) in both commit comments and the change log. If I now link to, github, etc and they “go away” (some way or the other), all of these links become invalid and I don’t have a chance to fix this (again, I’ve actually experienced that, so it’s not pure theory). And such things happen. For a non-rsyslog example, think about the bitkeeper debacle, where they out of the sudden thought it was due to charge kernel developers for so-far free services.

Again, I would really like to have some of the cool things. With git, it’s relatively safe, as I can move the repo around quickly, and as long as the site contains the main pointer to where the current official git is, the risk is very limited. But other than that, my experience is that the short-term benefits come at the risk of severe long-term problems.

I am open to really good arguments why I am wrong. One good argument would probably be an OSS complete hosting service that is in place for 15+ yrs without any interruption in user base and breaking URLs – and that is still a hot spot. I guess mostly qualifies in that category, but as I said, we had our own story with them…

I frankly admit that I am very conservative in this regard. After all, I even post things like this on my personal blog, and not on a site directly owned by Adiscon. But, you may say, you use blogger, so don’t you take a risk here? Well, you probably have noticed that I use blogger under a domain that I have full control over. So whenever they go crazy, I can move on to some other place (not totally effortlessly, but I am in control of those things).

rsyslog on github

In some pretty long discussions, it turned out that most (if not all) users were not aware that rsyslog has an official repository on  github for over six month now. So it probably is a good idea to tell the world.

While it probably is obvious, I would also like to say that I accept pull requests via github. Actually, this was always the case, even when I had no repository on github. If someone sends me a pull request, I fetch from whereever that someone’s git is located, merge it into my git and push the final result. So there is nothing special with a repository that’s on github.

Please note that we currently continue to provide rsyslog via the Adiscon git. With git, it’s irrelevat where a repository is hosted — git is not a server-based system. While I like github’s interface, I do not like to lock rsyslog into github. We almost got locked into in the early days of rsyslog development and I was extremely happy that we resisted to do much more than just the CVS repository on SF when they had their really bad time. Github currently for sure is the place to be, but I like the ability to move away when the next cool thing pops up. As such, I have setup a new page that describes where the rsyslog repositories can be found currently.  This page will be updated as need arises.

Please note that official repositories are peers, so all are equal (minus maybe a one-minute delta during push operations). Pick whichever you like most.