A new version of Altai Private Cloud for Developers 1.0.2 was released.
The new release is devoted to cleaning package dependencies. Also, a bunch of bugfixes was made, primarily to user interface. Let’s see what’s new in Altai 1.0.2 from maintainer’s point of view.
In previous releases, we had this motto: “Take basic CentOS/RHEL, take our source RPMs, and you will be able to build the whole Altai and install it”.
Altai RPMs (both source and binary) were grouped in two repositories: “main” and “deps”. “deps” were packages rebuilt from their third-party source RPMs without changes. All other packages went to “main”, including customized third-party software (like nginx with uploading module) and Altai proper packages like Focus web UI.
Since we built both “main” and “deps” packages, we signed them with Grid Dynamics signature.
This model had one pitfall: we had to maintain plenty of well-known packages that were not included into basic CentOS/RHEL, such as Rabbit MQ or Erlang. That made our repositories really tremendous: 500 MiB, 100 MiB for “main” and 400 for “deps”! Imagine how wasteful is add these tons of unchanged third-party packages to every release. That’s why we tried the following solution in the previous release (1.0.1): include a chain of repositories so almost all unchanged packaged are downloaded from 1.0.0 release and 1.0.1 repository contains only packages to upgrade. As it was shown in this article, YUM can handle thousands of repositories simultaneously without performance problems. So, the repository chain approach significantly saves space for newer releases, but it leads to some maintaining problems.
For example, imagine if one package should be downgraded in the next release. We can call
yum downgrade package-name in Altai installer, but how could we guarantee that this packages will not be updated later accidentally by user in a
yum update procedure?
A more complex problem is that it’s difficult to determine a list of all packages that belong to given release if they are spread between lots of repositories. Even more, build a new release repository being the next in the repo chain is a nontrivial task.
Fortunately, if you decide to use EPEL packages, you’ll say farewell to all these obstacles. First, the repository becomes significantly smaller just because now you haven’t to rebuild heaps of packages. Now we have only 160 MiB of binary packages. Second, with a small repository you haven’t to use cunning repository chain – everything becomes transparent and easy to support.
It’s worth to say that it using EPEL packages isn’t as simple as it seems to be. Some important Python libraries are installed in such places that you would have to patch your programs or they wouldn’t find their dependencies. We decided to reject these libraries and package them ourselves. Luckily, the most of EPEL packages were able to be used in Altai without complications.
As far as we reviewed all Altai packages, we chosen another repository layout. Let’s briefly describe it.
- centos6: these packages are maintained and developed by Grid Dynamics team. This group contains customized OpenStack and a lot of home-grown packages signed by Altai team. Sources of these packages are available at GitHub.
- deps: these packages are not a subject of Grid Dynamics development. This category includes the following subdirectories.
- centos6-updates – necessary update packages for CentOS 6 signed by CentOS.
- epel – necessary packages from EPEL repositories signed by EPEL.
- misc – packages built and signed by Altai team.
- misc-srpms – source RPMs for misc and signed by Altai team.
As you see, we still provide sources of all packages we’ve built as it’s appropriate for an open source project.
As it was mentioned above, we keep Altai sources in git. There are two steps between a git repository and a binary RPM. First, a source RPM must be built from a git repo. Second, a binary RPM is built from a source one.
Each step is a not-trivial operation. A source RPM must contain all information required for package build, including source tarball, spec file, and possibly patches that should be applied to unpacked tarball before build. ALT Linux team even developed a powerful toolkit called GEAR (Get Every Archive from git package Repository). GEAR contains tens of individual CLI programs for different purposes, including composing a source RPM from a git repository and importing a tarball to git. We used GEAR in previous releases, but the only feature we needed was git-to-source RPM conversion. Even more, almost every conversion was trivial because we develop software keeping in mind that they will be packaged to RPMs. GEAR, on its turn, allows to maintain third-party software that is under active or slow development and need to be patched before packaging.
Obviously, multifunctional GEAR led to boilerplate configuration files. That’s why we simplified git-to-source RPM conversion as in our case it could be done with a small and clear script. And there is now need to write GEAR rules file: it’s sufficient to just place a spec file to git repository.
Frankly speaking, the second step (source-to-binary RPM conversion) is trickier than the first, but, fortunately, there is a ready solution – mock tool used in Fedora and EPEL. mock prepares a clean and safe build chroot environment for build operation. We have already used mock for previous releases and we haven’t ceased to take its advantages.
So, Altai 1.0.2 is easy to develop, maintain, and support and in the same time more foolproof.