Re: [Hawkular-dev] Pozvánka: Discuss Inventory Sync - St 2016/04/20 3:30PM - 4:30PM (Hawkular)

The discussion we had revolved mainly about what does sync (or lack thereof) mean in the bigger picture of Hawkular. First, I will summarize the discussion and the main questions we raised (please fill in the gaps if you find I forgot about something) and then, in a subsequent email, I'll try to provide my answers to those questions to start off further discussion. == Should we delete stuff from inventory when it's not present in the sync report? On one hand, one could argue that yes, we should delete whatever the feed doesn't see, because, well, it isn't there and therefore inventory should not keep it, because then it would not represent what the true state of affairs is (this brings forth the missing versioning in inventory - if we had that, we would keep the historical record of the resource being there). On the other hand, users should "see something" when a resource they expect to exist suddenly disappears. Yet another stance on this is that if stuff is kept in inventory even after it has stopped being reported by feeds, it should not remain there forever (why is the app that I undeployed a month ago still showing up in inventory?). == What does time since last sync mean? Say we have an embedded Widfly agent that we haven't heard from for a year. Does it mean that there's just nothing new coming from it or it just means that the server the agent was running in no longer runs? And more importantly what should we do about it? The idea was to somehow store the time the last sync occurred and base further decisions on that. What this timestamp would mean would depend on what we're looking at. For a feed, this would mean the last time it synced and hence was running correctly. For a resource managed by a feed, this would mean the last time the feed saw that resource (provided we don't delete the resources during sync immediately upon not seeing them). For an embedded feed, not seeing it running either means that the server it's embedded in is not running or it also can mean that the feed was just "removed" from the server it was running in. For a standalone feed managing remote servers/processes, this would mean the feed is not running, but would not tell us anything about the servers it manages. == How do we determine what's "the last time we've seen something live?" This can be based on the last sync time or the last time we've seen some metric associated with a resource or the last time we've seen a (to be implemented) availability metric associated with a resource. == Conclusion The three questions raised above are intertwined and the answers to them will influence each other. Overall these questions revolve around determining staleness/age of the inventory data and how to react on it. On Tuesday, April 19, 2016 06:51:04 PM lkrejci(a)redhat.com wrote: -- Lukas Krejci