Merge Compute and Central agents

https://blueprints.launchpad.net/ceilometer/+spec/merge-central-and-compute-agents

Central agent was previously extracted from compute agent code to support not only compute metrics to be polled, but also to collect measurements from other services and resources. Actually the main difference between these two agents was in the way they discover and poll the resources. After the discovery was unified for the all pollsters, we actually are having the logic duplication, having two different agents, although they both discover and poll some resources and collect then some metrics.

It looks logical to merge the code of agents back. They even might have exactly the same pipeline being used, but differ only in the console script parameter –polling-namespace to have the opportunity still to separate them in the real deployment. Also that might be possible to define exact list of pollsters to be used via –pollster-list script parameter here.

Problem description

We have logic mismatch with two separated agents, although they might be part of one piece of code, configured via pipeline.

Proposed change

We need to merge carefully code of compute and central agents, using unified mechanism we already have to process discovery and polling processes.

Also we need to save the opportunity of setting up agent to poll only compute or only meters used to be polled by central agent. Basically all-in-one installation will be satisfied with agent polling all available meters, but production installations need this separation. This will be achieved by adding additional per-agent CLI script parameter: –polling-namespace={compute|central|compute,central} (with adding here ipmi when this agent will be added here as well). In this case running of polling agent will look like following:

ceilometer-polling –polling-namespace central compute –logfile /var/log/ceilometer/polling.log

This parameter will be passed to the agent manager class directly, and will define what setup.cfg namespace (ceilometer.poll.central, ceilometer.poll.compute or both) with possible pollsters to load. This will emulate current workflow (and probably become deprecated in next cycles).

Also this change will propose new way of how do pollsters to be used are chosen for polling agent instance - via CLI script parameter –pollster-list=<list of pollster entrypoints or wildcards>. In this case polling agent running command will look like this:

ceilometer-polling –pollster-list image image.size storage.* –logfile /var/log/ceilometer/polling.log

If both of these parameters will be set, we need to use them both (possibly using logical AND operation to find out final list of pollsters to be used).

Alternatives

None

Data model impact

None

REST API impact

None

Security impact

None

Pipeline impact

None

Other end user impact

None

Performance/Scalability Impacts

Better RAM usage in case of development OpenStack all-in-one installations.

Other deployer impact

  • It’ll be less services Ceilometer will run on node (if it’ll be all-in-one installation) and we’ll have more unified way of Ceilometer installation.

  • Downstream impact on how Ceilometer packages will be created and on the deployment tools that use them right now. Currrently we are having two separated packages for central and compute agents in Ceilometer (both for the .rpm and .deb), and these packages have different .service/.upstart definitions for launching the corresponding service. The simplest way to fix this moment will be to add new combined package and make current separated ones to use introduced in this change namespaces like below:

    s/ExecStart=...ceilometer-agent-compute/
      ExecStart=...ceilometer-agent-polling --pollster-namespace=compute/
  • We need to update puppet-ceilometer module and add there new manifest that will support combined agent.

Developer impact

None

Implementation

Assignee(s)

Primary assignee:
dbelova <dbelova@mirantis.com>

Work Items

  • Merge central agent code into the current compute one (ceilometer-polling). Leave ceilometer-agent-compute and ceilometer-agent-central CLI commands for a deprecation cycle.
  • Investigate Tempest testing impact and provide new tests if needed.
  • Provide Devstack with new agents scheme support (for all-in-one and multinode installations).
  • Investigate Grenade tests aspect.

Future lifecycle

None

Dependencies

None

Testing

This change needs to be tested by merged unit tests and via integration tests (old and possible new ones).

Documentation Impact

We’ll need to rewrite our installation guide and common documentation parts with the information about one agent instead of two.

References

None