[Hawkular-dev] Sync with Inventory

Lukas Krejci lkrejci at redhat.com
Wed Jun 29 09:20:32 EDT 2016 

Btw. I've slightly updated the inventory organization description on the 
hawkular site (http://www.hawkular.org/docs/components/inventory/
index.html#inventory-organization). I hope it explains the structure and 
intent of the entities in inventory in a slightly more comprehensible manner.

My answers are inline below...

On středa 29. června 2016 14:39:27 CEST Thomas Segismont wrote:
> Thank you very much for the thorough reply Lukas. A few
> questions/comments inline.
> 
> Le 23/06/2016 à 15:59, Lukas Krejci a écrit :
> > On Thursday, June 23, 2016 10:27:12 AM Thomas Segismont wrote:
> >> Hey Lukas,
> >> 
> >> Thank you for pointing us in the sync endpoint. Austin will look into
> >> this and will certainly come back with more questions.
> >> 
> >> With respect to the user creating resources question, the difference
> >> between Vert.x and Wildfly is that the user creates resources
> >> grammatically. So in version 1 of the application, there might be two
> >> HTTP servers as well as 7 event bus handlers, but only 1 http server in
> >> version 2. And a named worker pool in version 3.
> >> 
> >> In the end, I believe it doesn't matter if it's container which creates
> >> resources or if it's the user himself. Does it?
> > 
> > It does not really (inventory has just a single API, so it does not really
> > know who is talking to it - if a feed or if a user) - but resources inside
> > and outside feeds have slightly different semantics.
> > 
> > Right now the logic is this:
> > 
> > Feeds are "agents" that don't care about anything else but their own
> > little
> > "world". That's why they can create their own resource types, metric types
> > and they also declare resources and metrics of those types. Feed does not
> > need to look "outside" of its own data and is in full charge of it.
> 
> Does that mean that creating a feed is the only way to create
> resource/metric types?

No, you can also create resource types and metric types directly under the 
tenant.

> I suppose the benefit of creating resource types is that then you can
> search for different resources of the same type easily.
> 
> And if feeds create resource types, how do you know that resource types
> created by the Hawkular Agent feed running on server A are the same as
> those created by another agent running on server B?
>

Inventory automatically computes "identity hashes" of resource types and 
metric types - if 2 resource types in 2 feeds have the same ID and exactly the 
same configuration definitions, they are considered identical. If you know 1 
resource type, you can find all the identical ones using the following REST 
API (since 0.17.0.Final, the format of the URLs is thoroughly explained here: 
http://www.hawkular.org/docs/rest/rest-inventory.html#_api_endpoints):

/hawkular/inventory/traversal/f;feedId/rt;resourceTypeId/identical

If for example some resource types should be known up-front and "shared" 
across all feeds, some kind of "gluecode" could create "global" resource types 
under the tenant, that would have the same id and structure as the types that 
the feeds declare. If then you want to for example find all resources of given 
type, you can:

/hawkular/inventory/traversal/rt;myType/identical/rl;defines/type=resource

I.e. for all types identical to the global one, find all resources defined by 
those types.
 
> > Hence the /sync endpoint applies to a feed nicely - since it is in charge,
> > it merely declares what is the view it has currently of the "world" it
> > sees and inventory will make sure it has the same picture - under that
> > feed.
> > 
> > Now if you have an application that spans multiple vms/machines and is
> > composed of multiple processes, there is no such clear distinction of
> > "ownership".
> 
> Good point, Vert.x applications are often distributed and communicating
> over the EventBus.
> 
> > While indeed a "real" user can just act like a feed, the envisioned
> > workflow is that the user operates directly in environments and at the
> > top level. I.e. a user assigns feeds to environments (i.e. this feed
> > reports on my server in staging environment, etc) and the user creates
> > "logical" resources in the environment (i.e. "My App" resource in staging
> > env is composed of a load balancer managed by this feed, mongodb managed
> > by another feed there and clustered wflys there, there and there).
> > 
> > To model this, inventory supports 2 kinds of tree hierarchies - 1 created
> > using the "contains" relationship, which expresses existential ownership -
> > i.e. a feed contains its resources and if a feed disappears, so do the
> > resources, because no one else can report on them. The entities bound by
> > the
> How does a feed "disappear"? That would be by deleting it through the
> REST API, correct? Something the ManageIQ provider would do through the
> Ruby client?
> 

yes

> > contains relationship form a tree - no loops or diamonds in it (this is
> > enforced by inventory). But there can also be a hierarchy created using an
> > "isParentOf" relationship (which represents "logical" ownership).
> > Resources
> > bound by "isParentOf" can form an acyclic graph - i.e. 1 resource can have
> > multiple parents as well as many children (isParentOf is applicable only
> > to
> > resources, not other types of entities).
> > 
> > The hierarchies formed by "contains" and "isParentOf" are independent. So
> > you can create a resource "My App" in the staging environment and declare
> > it a parent (using "isParentOf") of the resources declared by feeds that
> > manage the machines where the constituent servers live.
> 
> Interesting, that may be the way to model a Vert.x app deployed on two
> machines. Each process would have its own feed reporting discovered
> resources (http servers, event bus handlers, ... etc), and a logical app
> resource as parent.
>

Exactly.
 
> > That is the envisaged workflow for "apps". Now the downside to that is
> > that
> > (currently) there is no "sync" for that. The reason is that the
> > application
> > really is a logical concept and the underlying servers can be repurposed
> > to
> > serve different applications (so if app stops using it, it shouldn't
> > really
> > disappear from inventory, as is the case with /sync - because if a feed
> > doesn't "see" a resource, then it really is just gone, because the feed is
> > solely responsible for reporting on it).
> 
> What happens to the resources exactly? Are they marked as gone or simply
> deleted?

Right now they are deleted. That is of course not optimal and versioning is in 
the pipeline right after the port of inventory to Tinkerpop3. Basically all 
the entities and relationships will get "from" and "to" timestamps. 
Implicitly, you'd look at the "present", but you'd be able to look at how 
things looked in the past by specifying a different "now" in your query.

> Do you know how dependent services are updated? For example, when a JMS
> queue is gone, are alert definitions on queue depth removed as well? How
> does that happen?
>

Inventory sends events on the bus about every C/U/D of every entity or 
relationship, so other components can react on that.
 
> > We can think about how to somehow help clients with "App sync" but I'm not
> > sure if having a feed for vertx is the right thing to do. On the other
> > hand I very well may not be seeing some obvious problems of the above or
> > parallels that make the 2 approaches really the same because the above
> > model is just ingrained in my brain after so many hours thinking about it
> > ;)
> > 
> >> As for the feed question, the Vert.x feed will be the Metrics SPI
> >> implementation (vertx-hawkular-metrics project). Again I guess it's not
> >> much different than the Hawkular Agent.
> > 
> > A feed would only be appropriate if vertx app never reported on something
> > that would also be reported by other agents. I.e. if a part of a vertx
> > application is also reported on by a wfly agent, because that part is
> > running in a wfly server managed by us, then that will not work - 1
> > resource cannot be "contained" in 2 different feeds (not just API wise,
> > but logically, too).
> I'm not too worried about this use case. First the vast majority of
> Vert.x applications I know about are not embedded. Secondly the Vert.x
> feed would not report resources already reported by the Hawkular Agent.
> 
> >> Maybe the wording around user creating resources was confusing? Did you
> >> thought he would do so from application code? In this case, the answer
> >> is no.
> > 
> > Yeah, we should probably get together and discuss what your plans are to
> > get on the same page with everything.
> 
> I believe that presenting to you (and to whoever is interested) the
> conclusions of investigations would be beneficial indeed.
> 

+1

> >> Regards,
> >> Thomas
> >> 
> >> Le 23/06/2016 à 10:01, Austin Kuo a écrit :
> >>> Yes, I’m gonna build the inventory for vertx applications.
> >>> So I have to create a feed for it.
> >>> 
> >>> Thanks!
> >>> 
> >>> On Tue, Jun 21, 2016 at 7:55 PM Lukas Krejci <lkrejci at redhat.com
> >>> 
> >>> <mailto:lkrejci at redhat.com>> wrote:
> >>>     Hi Austin,
> >>>     
> >>>     Inventory offers a /hawkular/inventory/sync endpoint that is used to
> >>>     synchronize the "world view" of feeds (feed being something that
> >>>     pushes data
> >>>     into inventory).
> >>>     
> >>>     You said though that a "user creates" the resources, so I am not
> >>>     sure if /sync
> >>>     would be applicable to your scenario. Would you please elaborate
> >>>     more on where
> >>>     in the inventory hierarchy you create your resources and how? I.e.
> >>>     are you
> >>>     using some sort of feed akin to Hawkular's Wildfly Agent or are you
> >>>     just
> >>>     creating your resources "manually" under environments?
> >>>     
> >>>     On Tuesday, June 21, 2016 02:20:33 AM Austin Kuo wrote:
> >>>     > Hi all,
> >>>     > 
> >>>     > I’m currently investigating how to sync with inventory server.
> >>>     > Here’s the example scenario:
> >>>     > Consider the following problem. A user creates version 1 of the
> >>>     
> >>>     app with
> >>>     
> >>>     > two http servers, one listening on port 8080, the other on port
> >>>     
> >>>     8181. In
> >>>     
> >>>     > version 2, the http server listening on port 8181 is no longer
> >>>     > needed.
> >>>     > When the old version is stopped and the new version started, there
> >>>     
> >>>     will be
> >>>     
> >>>     > just one http server listening. The application is not aware of
> >>>     > the
> >>>     > previous state. What should we do so that the second http server
> >>>     
> >>>     is removed
> >>>     
> >>>     > from Inventory?
> >>>     > 
> >>>     > Thanks in advance.
> >>>     
> >>>     --
> >>>     Lukas Krejci
> >>>     
> >>>     _______________________________________________
> >>>     hawkular-dev mailing list
> >>>     hawkular-dev at lists.jboss.org <mailto:hawkular-dev at lists.jboss.org>
> >>>     https://lists.jboss.org/mailman/listinfo/hawkular-dev
> >>> 
> >>> _______________________________________________
> >>> hawkular-dev mailing list
> >>> hawkular-dev at lists.jboss.org
> >>> https://lists.jboss.org/mailman/listinfo/hawkular-dev


-- 
Lukas Krejci

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