In April 2016, the Technology Operations team at the WMF did some work on the servers that run Wikipedia and the other wikis.  This resulted in all editing being stopped at all wikis for about half an hour on two different days. 

A similar project is currently expected sometime in April 2017.  I do not have specific dates or times yet.  However, I expect the first editing disruption to happen during the first half of April and the second to be about two weeks afterwards.  

They are hoping that the editing outages will be shorter this time (perhaps 15 to 30 minutes).  The time of day is undecided; however, it will almost certainly be when most of the Ops staff is online (afternoon in Europe and Africa/morning in the Americas).

Last year, the official schedule was kept at https://wikitech.wikimedia.org/wiki/Switch_Datacenter and the same page may be used again.  If you are scheduling short workshops during April, then please consider checking that schedule or checking with me before you finalize your plans.  If you need to reach me, then I am currently subscribed to the GLAM mailing list, and you can always leave a note on my talk page at https://en.wikipedia.org/wiki/User_talk:Whatamidoing_(WMF)