11 a.m.
<tl;dr>
Need ideas on how we are to implement the following two things in the agent:
1. At startup, agent needs to ask H-Metrics "what top-level servers have I told you
about in an earlier life?"
2. When a new server is discovered, the agent should send an event to the server about the
new server EXCEPT if the server isn't really new at all (see 1. above)
</tl;dr>
===
This post is to open up a discussion on how we want to implement a new features in the
agent.
Joel is developing a new "inventory in metrics" feature:
https://github.com/hawkular/hawkular-agent/pull/303
This means the agent will be storing inventory directly into Hawkular-Metrics. Because of
this, we need to figure out how to get events sent based on things happening in
H-Metric's inventory so MiQ can do things with it (like put things in the timeline
such as "new server discovered" or "new WAR was deployed").
Jay looked at the code and the only thing that would be "missing" after this
move of inventory into metrics is an event triggered when a new server is added to
inventory. (When a new deployment is added, or a deployment is removed, the server is
looking at command responses and generating events from that - so we don't lose
anything by moving inventory into metrics).
By "new server", what we mean is a new resource that has no parent resources
(i.e. a "root resource"). This includes standalone WildFly Servers and domain
Host Controllers.
Right now, the agent starts with a "clean slate" when it starts up for the first
time, or restarts. That means the agent's in-memory inventory graph is completely
empty at startup - when discovery is run, the agent's internal inventory graph is
filled in. After that, the agent just keeps the inventory graph up to date as it discovers
new things coming and old things going away.
We need the agent to know if it already stored its top level servers into H-Metrics
inventory and if it did, not to generate any "new server event". But if the
agent is brand new, and it never sent any top-level resources to H-Metrics inventory yet,
it should now send a "new server" event to the server (the agent never sent
events like this before).
So there are two new things (assuming we keep the stuff Joel is doing - that is, we store
inventory into H-Metrics):
1. At startup, agent needs to ask H-Metrics "what top-level servers have I told you
about in an earlier life?"
2. When a new server is discovered, the agent should send an event (whatever this means -
probably a REST API call somewhere) about the new server EXCEPT if the server isn't
really new at all (see 1. above)
We need to figure out how to implement 1. and 2. So we are soliciting thoughts on those
two subjects.