Hi Paul, As a technique to inquire about "why" questions, I sometimes find the original JIRA issue and/or PR and ask there. It may be a years-old issue/PR but I personally think nothing of it -- it's practical as it pings relevant people watching vs. a shot in the dark about an obscure matter.
~ David On Tue, Aug 22, 2023 at 3:51 PM Paul McArthur <pmcarthur-apa...@proton.me.invalid> wrote: > Hi all, > > I’m creating a cluster singleton plugin and have found an issue with the > lifecycle management of the singleton if the plugin is updated via the API. > > When the /cluster/plugin api is called with an update payload, the > ClusterSingletons.modified method is called, which adds the new plugin to > the singletonMap (and starts it if applicable). Then it stops and removes > the old one. The order of these operations has a couple of side effects: > > 1. For a very brief period, there are 2 instances of the plugin running. > This may not really be a problem, but does seem to violate the Singleton > principle > > 2. Given that the map is keyed on the plugin name, adding the replacement > first will overwrite the existing (old) entry in the map. Then when the old > one is removed, it actually removes the new one that was just added. This > leaves the singletonMap with no entry for the plugin. When the Overseer > node goes down, the stop method is not called for the plugin because it no > longer has an entry in the map. > > I’ve reproduced the issue by modifying the TestContainerPlugin test, and I > can create a Jira issue, but I wonder if there is any reason that the added > and deleted methods are called in this order that I haven’t understood. It > seems to me that reversing the order in which they are called will solve > the issue. > > Thanks, > Paul
