3:09 a.m.
On Fri, Dec 1, 2017 at 11:54 PM, John Mazzitelli <mazz(a)redhat.com> wrote:
Spent time trying to figure out how to support WildFly domain mode
with
the new stuff. It's not going well. Next week I will need to have some
discussions on how we want to do this.
The issues with domain mode (I'll try to be short):
1) host controllers do not emit JMX metrics for slave servers - just not
implemented in WildFly. Need to go to slave servers for their own JMX
metrics.
2) slave servers do not have managed interfaces available remotely (can't
connect to slaves over remote management interface - so agent can't get any
inventory from slaves - have to get all inventory from host controller)
This means our agent in the host controller needs to collect all inventory
for both master host controller and slave servers.
But we need the slave servers to have a metrics endpoint because its only
in the slaves where we can get JMX metrics (remember, host controller can't
give us that, we must scrape the slave servers for the JMX metrics).
If we do not have our agent in slave server (why bother if we can't
connect to it over DMR API to get inventory?), we still need to somehow get
the P8s JMX Exporter installed in the slaves. But if we just use the raw
jmx exporter agent, how do we tell our h-services server/P8s server about
the new endpoint that needs to be scraped? And how do we get the jmx
exporter yml config to install there?
So I suppose we should put our agent in a kind of "metrics only" mode in
all slave servers so it can expose the JMX exporter and pull down the
correct jmx exporter yml from h-services server and have it tell the server
to add the scrape endpoint to p8s.
But because we aren't getting inventory from slave servers, how can our
agent tell the server to add the scrape endpoint? Our current
implementation only adds scrape endpoints to our P8s server when new agents
go into inventory. Workaround: either have agent store a small inventory
(just the agent resource itself) which triggers the new scrape endpoint
addition, or add a inventory REST endpoint for the agent to call to add the
new scrape endpoint manually.
OK, assume we have all this. How do we link the JMX metrics getting
collected from one feed (the agent in the slave server) to the inventory
from another feed (the agent in the host controller). Right now, it is
assumed the inventory metadata from feed "A" is matched with metrics from
the same feed. Now that we have to break that link (feed A's inventory
refers to feed B's metrics) we need to figure out how to fix this.
There are other ancillary issues - like how do I get the correct metadata
defined for host controller so it can match resources/metrics from the
slaves. I assume that will be "implementation details."
I'm sure this sounds like gibberish, but that's how convoluted supporting
domain mode is going to be.
Mazz,
What about to promote the host controller agent as the responsible for
everything ?
- Host controller agent will be responsible to collect info of the domain
(slave servers) and write into the inventory (Domain, Server, etc).
- Slave server can have a "metrics-only" endpoint (perhaps same agent,
perhaps a *-domain.jar if we want to simplify things).
- Host controller agent can proxy slave metrics endpoint, so we can control
endpoints like /metrics-domain/<slave>/metrics and that is what inventory
uses to create the endpoint.
- Host controller will expose in a proxy way, the metrics endpoint for the
slaves.
This approach focus the complixity in the host controller, but let to not
have exceptions and corner use cases in the whole system, the benefit I see
is that from MiQ and Hawkular Services we can try to maintain and uniform
way.
So, as you point Host Controllers needs to know the topology of the domain,
and each slave should have a local /metrics which can be proxied from the
host controller main endpoint.
On this case, both Host Controllers and Slaves will share same feed,
because, they are using the same agent, and that won't break any design use
case.
Also, I think that this proxy has a minimal technical complexity, as the
host controller should have all info to expose that.
(note: none of this attempts to solve how we are going to get MiQ UI to
use this new inventory/metrics data - I have no idea if it will be trivial
or be convoluted, too)
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