[Hawkular-dev] Sync with Inventory

Wed Jun 29 08:39:27 EDT 2016

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?
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?

>
> 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?

> 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.

>
> 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?
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?

>
> 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.

>
>> 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
>>>
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>>>
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>

-- 
Thomas Segismont
JBoss ON Engineering Team