[Hawkular-dev] Command gateway and WF agent

[Jay Shaughnessy]

 > First, remember the MiQ UI is connected to Hawkular-Services server 
via websocket.

One small nit, the MIQ UI websocket connection is via our ruby gem, so 
really any user of the rubly client could, I think, utilize the cmdgw stuff.

 > ... HOWEVER, I believe Jay added some code that does interact with 
Inventory to do things like create relationships in inventory when new 
cluster entities are added.

There is no code in cmdgw doing any interaction with inventory.  In 
cmdgw we only declare the supported request/responses.  There are two 
aspects of hServices that interact with inventory.

The InventoryEventListener listens for JMS events publish by Inventory 
and is responsible for:

  * generating Added/Removed Server events to be consumed by MIQ
      o using events for various server types
  * generating "isClusteredWith" relationships for clustered servers
      o using events for JGroups Channels

Inventory will no longer be generating these events and this listener 
will likely have to go away.  Either the agent will need to start 
generating the events or we'll need a new component to drive off of the 
persisted inventory data in metrics.


The Feed BackFill mechanism:

  * Needs to get and set the avail metrics for a feed's resources when
    the feed goes down (detected either by lack of avail heartbeat, or
    via broken websocket).

We will need to replace the inventory traversal query with something 
based on the new metrics impl.


On 3/7/2017 9:26 AM, Joel Takvorian wrote:
> Nice explanation, thanks!
>
> On Tue, Mar 7, 2017 at 3:12 PM, John Mazzitelli <mazz at redhat.com 
> <mailto:mazz at redhat.com>> wrote:
>
>     > Can you explain to me what's the big picture of the command gateway? What's
>     > the chain of calls when, for instance, there's a new deployment
>     in Wildfly?
>
>     Joel asked this question - I figured it is good to post to h-dev,
>     too, since I'm sure others don't know this.
>
>     The "big picture" is:
>
>     First, remember the MiQ UI is connected to Hawkular-Services
>     server via websocket. The agents all connect to some
>     Hawkular-Services server via a websocket. There can be more than
>     one Hawkular-Services server running and the UI may be talking to
>     a server that is different than the server the agent is talking to:
>
>     UI <---websocket---> Server A
>                              ^
>                              |
>                        (message bus)
>                              |
>                              V
>                          Server B <---websocket---> agent
>
>
>     1) MiQ sends a JSON message over the websocket to a
>     Hawkular-Services server (Server A in the diagram above).
>     2) Hawkular-Services server A looks at the ResourcePath in the
>     message to determine what agent is responsible for managing that
>     resource.
>     3) Hawkular-Services server A addresses the message to the proper
>     agent and puts the JSON message on the agent's queue on the
>     message bus.
>     3b) At this point the Hawkular-Services server A sends back a JSON
>     message to the UI over the websocket that says "message forwarded
>     to the bus".
>     4) The Hawkular-Services server that has a websocket connection to
>     the targeted agent picks off that message from the bus (Server B
>     in the diagram)
>     5) That Hawkular-Services server B forwards the message to the
>     agent via its websocket connection.
>     6) Agent looks the the message's ResourcePath and the rest of the
>     JSON to determine what it needs to do. It does the action.
>
>     // now the process goes in reverse
>
>     7) Agent sends back a response to the server B over websocket
>     (either a success or fail message)
>     8) Server B takes response, figures out which UI the response
>     should go to, and puts it on message bus addressed to the correct UI
>     9) The Server A takes the response message off the bus
>     10) Server A sends the response message to the UI over its
>     websocket connection.
>
>
>     > Tell me if I'm correct, for what I've seen it's MIQ which,
>     though the ruby
>     > client, sends a websocket event, caught by the WF agent through
>     the command
>     > gateway. In the end, the WF agent will perform a full sync of
>     affected root
>     > resources in inventory. Is that correct?
>
>     In the case of a "Deployment" JSON message, yes, the agent will
>     trigger a full discovery scan so it can quickly discover the new
>     deployment you just added to WildFly.
>
>     > If that's correct, there's no direct interaction between
>     inventory and the
>     > command gateway. I'm asking because I hope we can keep the
>     command gateway
>     > messages unchanged, and change only places where there's direct
>     calls to
>     > the inventory rest api.
>
>     Most of the time, its just using ResourcePath API (just that
>     simple inventory POJO). HOWEVER, I believe Jay added some code
>     that does interact with Inventory to do things like create
>     relationships in inventory when new cluster entities are added.
>     That is why (I think) he did this commit. Though I can't remember
>     where this code is that builds inventory relationships - he'll
>     have to point that out. But I'm pretty sure there is some
>     inventory stuff going on under the covers for that stuff - more
>     than just using the canonical ResourcePath stuff.
>
>
>
>
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