(apologies for cross-posting)
On either Thursday or Friday of this week, Giuseppe Lavagetto (of the Wikimedia TechOps team) and I are planning to migrate < https://test.wikipedia.org/%3E (testwiki) to HHVM. The way testwiki is configured makes it a natural next step on the path leading from the Beta Cluster to production. Specifically, testwiki is served by the same load-balancer, reverse-proxy, and database servers as the rest of production, but it is powered by a single application server that is segregated from the pool of servers that handle requests for all other Wikimedia wikis. This means that if we run into stability issues with HHVM, they will be confined to just testwiki, and will not spill over to other sites.
To migrate testwiki to HHVM, Giuseppe will need to take the server that powers testwiki off-line for several hours for re-imaging. Ordinarily, we design our infrastructure for redundancy and graceful failover, so we can take machines offline without impacting users. But the corollary to testwiki being a special case is that it is not configured in this way. As I explained above, this is just as well, because it means we can perform this work without disturbing the rest of the cluster.
Giuseppe and I will provide additional notices via IRC and e-mail prior to beginning this work. We know that testwiki is used by a diverse user-base to test various MediaWiki software components and will do our best to minimize disruption to such users. Feel free to get in touch via e-mail or IRC (my nickname is 'ori') if you have concerns about the deployment.
Thanks for your patience and understanding! :)
Ori