On large-scale Jenkins instances master disk and network I/O become bottlenecks in particular cases. Build logging and artifact storage were one for the most intensive I/O consumers, hence it would be great to somehow redirect them to an external storage. Back in 2016 there were active discussions about such Pluggable Storage for Jenkins. At that point we created several prototypes, but then other work took precedence. There was still a high demand in Pluggable Storage for large-scale instances, and these stories also become a major obstacle for cloud native Jenkins setups.

I am happy to say that the Pluggable Storage discussions are back online. You may have seen changes in the Core for Artifact Storage (JEP-202) and a new Artifact Manager for S3 plugin. We have also created a number of JEPs for External Logging and created a new Cloud Native Special Interest Group (SIG) to offer a venue for discussing changes and to keep them as open as possible.

Tomorrow Jesse Glick and I will be presenting the current External Logging designs at the Cloud Native SIG online meeting, you can find more info about the meeting here. I decided that it is a good time to write about the new SIG. In this blogpost I will try to provide my vision of the SIG and its purpose. I will also summarize the current status of the activities in the group.

What are Special Interest Groups?

If you follow the developer mailing list, you may have seen the discussion about introducing SIGs in the Jenkins project. The SIG model has been proposed by R. Tyler Croy, and it largely follows the successful Kubernetes SIG model. The objective of these SIGs is to make the community more transparent to contributors and to offer venues for specific discussions. The idea of SIGs and how to create them is documented in JEP-4. JEP-4 is still in Draft state, but a few SIGs have been already created using that process: Platform SIG, GSoC SIG and, finally, Cloud Native SIG.

SIGs are a big opportunity to the Jenkins project, offering a new way to onboard contributors who are interested only in particular aspects of Jenkins. With SIGs they can subscribe to particular topics without following the entire Developer mailing list which can become pretty buzzy nowadays. It also offers company contributors a clear way how to join community and participate in specific areas. This is great for larger projects which cannot be done by a single contributor. Like JEPs, SIGs help focus and coordinate efforts.

And, back to major efforts…​ Lack of resources among core contributors was one of the reasons why we did not deliver on Pluggable Storage stories back in 2016. I believe that SIGs can help fix that in Jenkins, making it easier to find groups with the same interests and reach out to them in order to organize activity. Regular meetings are also helpful to get such efforts moving.

Points above are the main reasons why I joined the Cloud Native SIG. Similarly, that’s why I decided to create a Platform SIG to deliver on major efforts like Java 10+ support in Jenkins. I hope that more SIGs get created soon so that contributors could focus on areas of their interest.

Cloud Native SIG

In the original proposal Carlos Sanchez, the Cloud Native SIG chair, has described the purpose of the SIG well. There has been great progress this year in cloud-native-minded projects like Jenkins X and Jenkins Essentials, but the current Jenkins architecture does not offer particular features which could be utilized there: Pluggable Storage, High Availability, etc. There are ways to achieve it using Jenkins plugins and some infrastructure tweaks, but it is far from the out-of-the-box experience. It complicates Jenkins management and slows down development of new cloud-native solutions for Jenkins.

So, what do I expect from the SIG?

  • Define roadmap towards Cloud-Native Jenkins architecture which will help the project to stay relevant for Cloud Native installations

  • Provide a venue for discussion of critical Jenkins architecture changes

  • Act as a steering committee for Jenkins Enhancement Proposals in the area of Cloud-Native solutions

  • Finally, coordinate efforts between contributors and get new contributors onboard

What’s next in the SIG?

The SIG agenda is largely defined by the SIG participants. If you are interested to discuss particular topics, just propose them in the SIG mailing list. As the current SIG page describes, there are several areas defined as initial topics: Artifact Storage, Log Storage, Configuration Storage

All these topics are related to the Pluggable Storage Area, and the end goal for them is to ensure that all data is externalized so that replication becomes possible. In addition to the mentioned data types, discussed at the Jenkins World 2016 summit, we will need to externalize other data types: Item and Run storage, Fingerprints, Test and coverage results, etc. There is some foundation work being done for that. For example, Shenyu Zheng is working on a Code Coverage API plugin which would allow to unify the code coverage storage formats in Jenkins.

Once the Pluggable Storage stories are done the next steps are true High Availability, rolling or canary upgrades and zero downtime. At that point other foundation stories like Remoting over Kafka by Pham Vu Tuan might be integrated into the Cloud Native architecture to make Jenkins more robust against outages within the cluster. It will take some time to get to this state, but it can be done incrementally.

Let me briefly summarize current state of the 3 focuses listed in the Cloud Native SIG.

Artifact Storage

There are many existing plugins allowing to upload and download artifacts from external storage (e.g. S3, Artifactory, Publish over SFTP, etc., etc.), but there are no plugins which can do it transparently without using new steps. In many cases the artifacts also get uploaded through master, and it increases load on the system. It would be great if there was a layer which would allow storing artifacts externally when using common steps like Archive Artifacts.

Artifact storage work was started this spring by Jesse Glick, Carlos Sanchez and Ivan Fernandez Calvo before the Cloud Native SIG was actually founded. Current state:

  • JEP-202 "External Artifact Storage" has been proposed in the Jenkins community. This JEP defines API changes in the Jenkins core which are needed to support External artifact managers

  • Jenkins Pipeline has been updated to support external artifact storages for archive/unarchive and stash/unstash

  • New Artifact Manager for S3 plugin reference implementation of the new API. The plugin is available in main Jenkins update centers

  • A number of plugins has been updated in order to support external artifact storage

The Artifact Manager API is available in Jenkins LTS starting from 2.121.1, so it is possible to create new implementations using the provided API and existing implementations. This new feature is fully backward compatible with the default Filesystem-based storage, but there are known issues for plugins explicitly relying on artifact locations in JENKINS_HOME (you can find a list of such plugins here). It will take a while to get all plugins supported, but the new API in the core should allow migrating plugins.

I hope we will revisit the External Artifact Storage at the SIG meetings at some point. It would be a good opportunity to do a retrospective and to understand how to improve the process in SIG.

Log storage

Log storage is a separate big story. Back in 2016 External logging was one of the key Pluggable Storage stories we defined at the contributor summit. We created an EPIC for the story (JENKINS-38313) and after that created a number of prototypes together with Xing Yan and Jesse Glick. One of these prototypes for Pipeline has recently been updated and published here.

Jesse Glick and Carlos Sanchez are returning to this story and plan to discuss it within the Cloud Native SIG. There are a number of Jenkins Enhancement proposals which have been submitted recently:

  • JEP-207 - External Build Logging support in the Jenkins Core

  • JEP-210 - External log storage for Pipeline

  • Draft JEP - External Logging API Plugin

  • JEP-206 - Use UTF-8 for Pipeline build logs

In the linked documents you can find references to current reference implementations. So far we have a working prototype for the new design. There are still many bits to fix before the final release, but the designs are ready for review and feedback.

This Tuesday (Jul 31) we are going to have a SIG meeting in order to present the current state and to discuss the proposed designs and JEPs. The meeting will happen at 3PM UTC. You can watch the broadcast using this link. Participant link will be posted in the SIGs Gitter channel 10 minutes before the meeting.

Configuration storage

This is one of the future stories we would like to consider. Although configurations are not big, externalizing them is a critical task for getting highly-available or disposable Jenkins masters. There are many ways to store configurations in Jenkins, but 95% of cases are covered by the XmlFile layer which serializes objects to disk and reads them using the XStream library. Externalizing these XmlFiles would be a great step forward.

There are several prototypes for externalizing configurations, e.g. in DotCI. There are also other implementations which could be upstreamed to the Jenkins core:

  • Alex Nordlund has recently proposed a pull request to Jenkins Core, which should make the XML Storage pluggable

  • James Strachan has implemented similar engine for Kubernetes in the kubeify prototype

  • I also did some experiments with externalizing XML Storages back in 2016

The next steps for this story would be to aggregate implementations into a single JEP. I have it in my queue, and I hope to write up a design once we get more clarity on the External logging stories.

Conclusions

Special Interest Groups are a new format for collaboration and disucssion in the Jenkins community. Although we have had some work groups before (Infrastructure, Configuration-as-Code, etc.), introduction of SIGs sets a new bar in terms of the project transparency and consistency. Major architecture changes in Jenkins are needed to ensure its future in the new environments, and SIGs will help to boost visibility and participation around these changes.

If you want to know more about the Cloud Native SIG, all resources are listed on the SIG’s page on jenkins.io. If you want to participate in the SIG’s activities, just do the following:

  1. Subscribe to the mailing list

  2. Join our Gitter channel

  3. Join our public meetings

I am also working on organizing a face-to-face Cloud Native SIG meeting at the Jenkins Contributor Summit, which will happen on September 17 during DevOps World | Jenkins World in San Francisco. If you come to DevOps World | Jenkins World, please feel free to join us at the contributor summit or to meet us at the community booth. Together with Jesse and Carlos we are also going to present some bits of our work at the A Cloud Native Jenkins talk.

Stay tuned for more updates and demos on the Cloud-Native Jenkins fronts!

About the Author
Oleg Nenashev

R&D and Automation engineer with Hardware/Embedded background. He started using Hudson/Jenkins in 2008 and became an active contributor in 2012. Oleg maintains Jenkins core, Remoting and several plugins. He organizes events like Jenkins meetups and GSoC in the community. Nowadays Oleg works at CloudBees on making Jenkins cloud-native.