GerritHub.io has been successfully migrated Gerrit Code Review v2.15. Thanks to the 5-days Gerrit Hackathon hosted by Axis in Lund, all the remaining issues we had on v2.15 have been resolved and all the 15k active users of GerritHub from today can use the 100% feature complete PolyGerrit UX.

What is PolyGerrit?

PolyGerrit is the code-name of the new UX wholly redesigned using web components, a set of web platform APIs that allow you to create new custom, reusable, encapsulated HTML tags to use in web pages and web apps. Custom components and widgets build on the Web Component standards, will work across modern browsers, and can be used with any JavaScript library or framework that works with HTML.

To access the PolyGerrit, just go to the GerritHub.io footer and click on the link “Switch to New UI” or add “?polygerrit=1” as an extra query string (e.g. https://review.gerrithub.io/?polygerrit=1)

To have a more comprehensive description of PolyGerrit, you can read the previous blog post about the Google talk at the past Gerrit User Summit in London.

Zero-downtime “ping-pong” migration to Gerrit v2.15

As usual, we migrated with near-zero-downtime, with only a “ten minutes *read-only* window” where we were waiting to drain the final replications were moved between Data-Centers.

There are two Data-Centers (DC) active for GerritHub.io; the main one is hosted in Canada and the second in Germany. Both DC have a high-availability configuration and run the same version of Gerrit with the same data. However, during major upgrades, we use a “ping-pong” technique to give a seamless experience to the users.

Ping phase

DC-Canada is with Gerrit v2.14 and DC-Germany gets upgraded to v2.15. Traffic gets forwarded smoothly from DC-Canada to DC-Germany thanks to the HAProxy that is serving traffic for https://review.gerrithub.io.

Pong phase

DC-Canada gets upgraded to v2.15 and DC-Germany sync back to Canada in near-real time. Once the upgrade is complete, the HAProxy forwards back the traffic to DC-Canada.

Benefits of the ping-pong upgrade

There two significant benefits of using the combined zero-downtime rollout with the ping-pong technique:

1. No general service disruption, minimal read-only time.
   Nobody would notice any significant service disruption on GerritHub.io: the read-only window is a minor service degradation that lasts for only a few minutes. Given that 90% of the traffic is represented by “git fetch/clone” and web browsing, the degradation is hardly noticed by anyone.
2. Validation of the disaster recovery procedure.
   Because the DC-Germany is used as disaster recovery site, it is essential to make sure that is always working fine and you can actually failover to it at any given time when needed.
   You do not want to find out that the disaster recovery isn’t working when is too late.

What’s new in Gerrit v2.15?

There are many changes in Gerrit v2.15, for the details you can have a look at the Google presentation at the Gerrit User Summit 2017 in London.

In a nutshell, here are the headlines of the most visible changes you will notice:

1. Support for draft changes and draft patch sets has been completely removed.
   You have now two possible states for a change: WIP (work-in-progress) and Private. All the changes that were in “draft” status at the migration have been moved to WIP state.
2. New URL Scheme
   Gerrit URLs generated and used by the UI include not just the change number but the project name as well.
   For instance, the Change 123 on project ‘myproject’ would now be accessible on the URL: https://review.gerrithub.io/#/c/myproject/+/123.
   Existing URLs containing only the change number (e.g. https://review.gerrithub.io/123) are redirected to the new scheme.
3. New workflows on the PolyGerrit UX
   The PolyGerrit UX is now 100% feature complete. It is not only an engineering rewrite but also a whole redesign of the user-flows and experience.
   See at https://www.gerritcodereview.com/releases/2.15.md#new-workflows the details of all the new flows.

What’s next?

Gerrit v2.15 includes a brand-new storage for reviews, code-named “NoteDb”, that is actually your Git repository itself. That means that all the meta-data, comments, scores, history, audit, will all be stored in the same GitHub repository with your code.

Our next step is to perform an online migration from ReviewDb to NoteDb, which will be again with zero-downtime. Thanks to the fantastic work made by Dave Borowitz (Google), there will be no need for a read-only window: you will not even notice.

What do know all the details of Gerrit v2.15?

For an overview of what’s new in GerritHub with v2.15, you can look at the Gerrit User Summit 2017 presentation.