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All Hail ResultsDB

Nov 07, 2016 | categories: factory2, fedora View Comments

This post is primarily about taking some of the lessons we learned in Fedora QA infrastructure and applying them to some internal Red Hat pipelines as well as generalizing the pattern to other parts of Fedora's infrastructure.

ResultsDB

  • ResultsDB is a database for storing results. Unsurprising!
  • It is a passive system, it doesn't actively do anything.
  • It has a HTTP REST interface. You POST new results to it and GET them out.
  • It was written by Josef Skladanka of Tim Flink's Fedora QA team.

It was originally written as a part of the larger Taskotron system, but we're talking about it independently here because it's such a gem!

What problems can we solve with it?

In formal Factory 2.0 problem statement terms, this helps us solve the Serialization and Automation problems directly, and indirectly all of the problems that depend on those two.

Beyond that, let's look at fragmentation. The goal of the "Central CI" project in Red Hat was to consolidate all of the fragmentation around various CI solutions. This was a success in terms of operational and capex costs -- instead of 100 different CI systems running on 100 different servers sitting under 100 different desks, we have one Central CI infrastructure backed by OpenStack serving on-demand Jenkins masters. Win. A side-effect of this has been that teams can request and configure their own Jenkins masters, without commonality in their configuration. While teams are incentivized to move to a common test execution tool (Jenkins), there's no common way to organize jobs and results. While we reduced fragmentation at one level, it remains untouched at another. People informally speak of this as the problem of "the fourteen Jenkins masters" of Platform QE.

Beyond Jenkins, some Red Hat PnT DevOps tools perform tasks that are QE-esque but yet are not a part of the Central CI infrastructure. Notably, the Errata Tool (which plays a very similar role to Fedora's Bodhi system) directly runs jobs like covscan, rpmgrill, rpmdiff, and TPS/insanity that are unnecessarily tied to the "release checklist" phase of the workflow. They could benefit from the common infrastructure of Central CI. (The Errata Tool developers are burdened by having to think about scheduling and storing test results while developing the release checklist application. This thing is too big.)

One option could be to attempt to corral all of the various dev and QE groups into getting onto the same platform and configuring their jobs the same way. That's a possibility, but there is a high cost to achieving that level of social coordination.

Instead, we intend to use resultsdb and a small number of messagebus hooks to insulate consuming services from the details of job execution.

Getting data out of resultsdb

Resultsdb, unsurprisingly, stores results. A result must be associated with a testcase, which is just a namespaced name (for example, general.rpmlint). It must also be associated with an item, which you can think about as the unique name of a build artifact produced by some RCM tool: the nevra of an rpm is a typical value for the item field indicating that a particular result is associated with a particular rpm.

Generally

Take a look at some examples of queries to the Fedora QA production instance of taskotron, to get an idea for what this thing can store:

For the Release Checklist

For the Errata Tool problems described in the introduction, we need to:

  • Set up Jenkins jobs that do exactly what the Errata Tool processes do today: rpmgrill, covscan, rpmdiff, TPS/Insanity. Ondrej Hudlicky's group is working on this.
  • We need to ingest data from the bus about those jobs, and store that in resultsdb. The Factory 2.0 team will be working on that.
  • We also need to write and stand up an accompanying waiverdb service, that allows overriding an immutable result in resultsdb. We can re-use this in Fedora to level up the Bodhi/taskotron interaction.
  • The Errata Tool needs to be modified to refer to resultsdb's stored results instead of its own.
  • We can decommission Errata Tool's scheduling and storage of QE-esque activities. Hooray!

Note that, in Fedora the Bodhi Updates System already works along these lines to gate updates on their resultsdb status. A subset of testcases are declared as required. However, if a testcase is failing erroneously, a developer must change the requirements associated with the update to get it out the door. This is silly. Writing and deploying something like waiverdb will make that much more straightforward.

On expanding this pattern in Fedora

Note also that the fedimg tool, used to upload newly composed images to AWS, currently has no gating in place at all. It uploads everything. While talking about how we actually want to introduce gating into its workflow, it was proposed that it should query the cloud-specific test executor called autocloud. Our answer here should be no. Autocloud should store its results in resultsdb, and fedimg should consult resultsdb to know if an image is good or not. This insulates fedimg's code from the details of autocloud and enables us to more flexibly change out QE methods and tools in the future.

For Rebuild Automation

For Fedora Modularity, we know we need to build and deploy tools to automate rebuilds. In order to avoid unnecessary rebuilds of Tier 2 and Tier 3 artifacts, we'll want to first ensure that Tier 1 artifacts are "good". The rebuild tooling we design will need to:

  • Refer to resultsdb to gather testcase results. It should not query test-execution systems directly for the reasons mentioned above.
  • Have configurable policy. Resultsdb gives us access to all test results. Do we block rebuilds if one test fails? How do we introduce new experimental tests while not blocking the rebuild process? A constrained subset of the total set of testcases should be used on a per-product/per-component basis to define the rebuild criteria: a policy.

Putting data in resultsdb

  • Resultsdb receives new results by way of an HTTP POST.
  • In Fedora, the Taskotron system puts results directly into resultsdb.
  • Internally, we'll need a level of indirection due to the social coordination issue described above. Any QE process that wants to have its results stored in resultsdb (and therefore be considered in PnT DevOps rebuild and release processes) will need to publish to the unified message bus or the CI-bus using the “CI-Metrics” format driven by Jiri Canderle.
  • The Factory 2.0 team will write, deploy and maintain a service that listens for those messages, formats them appropriately, and stores them in resultsdb.
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