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Thomas H Jones II
Thomas H Jones II

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Travis, EL7 and Docker-Based Testing

As noted in a prior post, a lot of my customer-oriented activities support deployment within networks that are either partially- or wholly-isolated from the public Internet. Yesterday, as part of supporting one such customer, I stood up a new project to help automate the creation of yum repository configuration RPMs for private networks. I've had to hand-jam such files twice, now, and there's unwanted deltas between the two jam-sessions (in my defense, they were separated from each other by nearly a three-year time-span ..and, each time, I'd figured the repositories' owners would be responsible enough to create and distribute their own configuration RPMs). So, I figured it was time to standardize and automate things.

Usually, when I stand up a project, I like to include tests of the content that I wish to deliver. Since most of my projects are done in public GitHub repositories, I typically use TravisCI to automate my testing. Prior to this project, however, I wasn't trying to automate the validity-testing of RPM recipes via Travis. Typically, when automating creation of RPMs I wish to retain or deliver, I set up a Jenkins job that takes the resultant RPMs and stores them in Artifactory – both privately-hosted services. Most of my prior Travis jobs were simple, syntax-checkers (using tools like shellcheck, JSON validators, CFn validators, etc.) rather than functionality-checkers.

This time, however, I was trying to deliver a functionality (RPM spec files that would be used to generate source files from templates and package the results). So, I needed to be able to test that a set of spec files and source-templates could be reliably-used to generate RPMs. This meant, I needed my TravisCI job to generate "throwaway" RPMs from the project-files.

The TravisCI system's test-hosts are Ubuntu-based rather than RHEL or CentOS based.While there are some tools that will allow you to generate RPMs on Ubuntu, there've been some historical caveats on their reliability and/or representativeness. So, my preference was to be able to use a RHEL or CentOS-based context for my test-packagings. Fortunately, TravisCI does offer the ability to use Docker on their test-hosts.

In general, setting up a Docker-oriented job is relatively straight forward. Where things get "fun" is that the version of rpmbuild that comes with Enterprise Linux 7 gets kind of annoyed if it's not able to resolve the UIDs and GIDs of the files it's trying to build from (never mind that the build-user inside the running Docker-container is "root" ...and has unlimited access within that container). If it can't resolve them, the rpmbuild tasks fail with a multitude of not terribly helpful "error: Bad owner/group: /path/to/repository/file" messages.

After googling about, I ultimately found that I needed to ensure that the UIDs and GIDs of the project-content need to exist within the Docker-container's /etc/passwd and /etc/group files, respectively. Note: most of the "top" search results Google returned to me indicated that the project files needed to be chowned. However, simply being mappable proved to be sufficient.

Rounding the home stretch...

To resolve the problem, I needed to determine what UIDs and GIDs the project-content had inside my Docker-container. That meant pushing a Travis job that included a (temporary) diagnostic-block to stat the relevant files and return me their UIDs and GIDs. Once the UIDs and GIDs were determined, I needed to update my Travis job to add relevant groupadd and useradd statements to my container-preparation steps. What I ended up with was.

    sudo docker exec centos-${OS\_VERSION} groupadd -g 2000 rpmbuilder
    sudo docker exec centos-${OS\_VERSION} adduser -g 2000 -u 2000 rpmbuilder

It was late in the day, by this point, so I simply assumed that the IDs were stable. I ran about a dozen iterations of my test, and they stayed stable, but that may have just been "luck". If I run into future "Bad owner/group" errors, I'll update my Travis job-definition to scan the repository-contents for their current UIDs and GIDs and then set them based on those. But, for now, my test harness works: I'm able to know that updates to existing specs/templates or additional specs/templates will create working RPMs when they're taken to where they need to be used.

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