feat: add metrics_optional_domains and metrics_optional_packages for users to configure optional domains

[richm]

Feature: The metrics role has access to many data collection domains.
The metrics role will automatically enable
domains for features being managed e.g. the metrics role will automatically
enable the elasticsearch domain if metrics_from_elasticsearch: true. The
new parameter metrics_optional_domains allows the user to provide a list
of additional domains to enable. The new parameter metrics_optional_packages
allows the user to provide a list of additional packages that may be required
to support the additional domains.

Reason: Users should be able to enable domains other than the ones for
features managed by the metrics role, and provide additional packages needed
to enable those domains.

Result: Users can enable the domains they need to use, and specify additional
packages required for those domains.

Signed-off-by: Rich Megginson rmeggins@redhat.com

Summary by Sourcery

Introduce support for user-configurable optional PCP agents in the metrics role, allowing users to enable additional agents beyond those automatically managed by the role.

New Features:

• Add metrics_optional_domains variable to allow users to specify additional domains to enable.

Enhancements:

• Update task logic to enable both automatically managed and user-specified PCP agents.

Documentation:

• Document the new metrics_optional_domains variable and its usage in README.md.

Tests:

• Add test coverage for enabling optional PCP agents via metrics_optional_domains.

[sourcery-ai]

Reviewer's Guide

This pull request adds a new parameter, metrics_pcp_optional_agents, enabling users to specify additional PCP agents to be enabled beyond those automatically managed by the metrics role, with corresponding updates to documentation, defaults, implementation logic, and tests.

File-Level Changes

Change	Details	Files
Introduced the metrics_pcp_optional_agents parameter to allow users to specify additional PCP agents to enable.	Added documentation for metrics_pcp_optional_agents in README.md, including usage example. Defined metrics_pcp_optional_agents with a default empty list in defaults/main.yml. Modified the PCP agent configuration logic to merge user-specified optional agents with automatically managed agents in tasks/main.yml. Updated test playbook to include metrics_pcp_optional_agents in tests/tests_verify_fullstack.yml.	README.md defaults/main.yml tasks/main.yml tests/tests_verify_fullstack.yml

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[sourcery-ai]

Hey @richm - I've reviewed your changes and they look great!

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[natoscott]

We've not included the backend project name ('pcp') directly in any variables before, don't think we should start now. How about 'metrics_optional_domains' instead here?

[richm]

@natoscott 1) What optional agents should this test with? Ideally, agents that are available in el7 - el10 and fedora. 2) How to verify that the optional agents are active/enabled?

[natoscott]

1. What optional agents should this test with? Ideally, agents that are available in el7 - el10 and fedora.

The apache agent (pcp-pmda-apache rpm) has been around forever and is never default installed in pmcd.conf - it is also tolerant of Apache not running, so seems like it might be a good option.

2. How to verify that the optional agents are active/enabled?

A good way is to ask pmcd via:

$ pminfo -f pmcd.agent.status | grep apache
    inst [68 or "apache"] value 0

Alternatively, can request values from the agent - this is problematic for CI though because it requires the source of metrics for that domain (apache) to be available, accessible and configured - which is not necessarily the case. From memory there are existing tests using pmcd.agent.status so I recommend that approach.

[richm]

@natoscott one catch is that I had to add this:

  vars:
    ...
    pcp_optional_packages: [pcp-pmda-apache]

which works - but it begs the question - how will customers install the custom packages required for metrics_optional_domains? Do we need to add a metrics_optional_packages which sets pcp_optional_packages?

[richm]

@natoscott on an unrelated topic - any idea why tests_verify_from_spark.yml test is failing? I can reproduce locally - this is supposed to work: pmprobe -I openmetrics.control.status but I get openmetrics.control.status -12357 Unknown metric name and pmprobe -I | grep openmetrics shows nothing.

[natoscott]

@natoscott on an unrelated topic - any idea why tests_verify_from_spark.yml test is failing? I can reproduce locally - this is supposed to work: pmprobe -I openmetrics.control.status but I get openmetrics.control.status -12357 Unknown metric name and pmprobe -I | grep openmetrics shows nothing.

Hi @richm - had a look through but couldn't see a root cause - the check has 10x 1sec retry logic, which is definitely needed to give pmdaopenmetrics time to start. The next thing to do would be to check both /var/log/pcp/pmcd/{pmcd,openmetrics}.log files for additional clues.

I'm guessing it just takes too long to get started, though on my local machine it completes in less than 1sec - the lack of any output from pminfo/pmprobe at all for the openmetrics.control.status metric suggests the PMDA is not yet completely setup. Another check that could be added is the pmcd.agent.status based check from check_from_elasticsearch.yml (with .find("openmetrics") instead) - this will let us know that pmcd has started the PMDA at least.

[richm]

@natoscott on an unrelated topic - any idea why tests_verify_from_spark.yml test is failing? I can reproduce locally - this is supposed to work: pmprobe -I openmetrics.control.status but I get openmetrics.control.status -12357 Unknown metric name and pmprobe -I | grep openmetrics shows nothing.

Hi @richm - had a look through but couldn't see a root cause - the check has 10x 1sec retry logic, which is definitely needed to give pmdaopenmetrics time to start.

I tried retries: 120 - same result - does not work

The next thing to do would be to check both /var/log/pcp/pmcd/{pmcd,openmetrics}.log files for additional clues.

I don't see openmetrics.log

I don't see any errors or other clues in pmcd.log

I'm guessing it just takes too long to get started, though on my local machine it completes in less than 1sec - the lack of any output from pminfo/pmprobe at all for the openmetrics.control.status metric suggests the PMDA is not yet completely setup. Another check that could be added is the pmcd.agent.status based check from check_from_elasticsearch.yml (with .find("openmetrics") instead) - this will let us know that pmcd has started the PMDA at least.

# pmprobe -I pmcd.agent.status
pmcd.agent.status 11 "root" "pmcd" "proc" "pmproxy" "xfs" "linux" "nfsclient" "mmv" "kvm" "jbd2" "dm"

I'm baffled . . .

[richm]

I'm testing locally like this:

tox -e qemu-ansible-core-2.19 -- --image-name centos-10 --log-level debug -- tests/tests_verify_from_spark.ym

pcp-pmda-openmetrics-6.3.7-5.el10.x86_64

[natoscott]

@richm I think we're missing something to stitch the needed agent in at the top level, e.g.

$ git diff
tasks/main.yml
--- /tmp/git-blob-xTgL42/main.yml       2025-07-22 11:23:16.334441108 +1000
+++ tasks/main.yml      2025-07-22 11:23:15.192109410 +1000
@@ -31,6 +31,11 @@
     __metrics_domains: "{{ __metrics_domains + ['elasticsearch'] }}"
   when: metrics_from_elasticsearch | d(false) | bool
 
+- name: Add OpenMetrics to metrics domain list
+  set_fact:
+    __metrics_domains: "{{ __metrics_domains + ['openmetrics'] }}"
+  when: metrics_from_spark | d(false) | bool
+
 - name: Add SQL Server to metrics domain list
   set_fact:
     __metrics_domains: "{{ __metrics_domains + ['mssql'] }}"

[richm]

#246

[natoscott]

@natoscott one catch is that I had to add this:
[...]
which works - but it begs the question - how will customers install the custom packages required for metrics_optional_domains? Do we need to add a metrics_optional_packages which sets pcp_optional_packages?

Yep, good point - I think that will be needed here.

[richm]

@natoscott one catch is that I had to add this:
[...]
which works - but it begs the question - how will customers install the custom packages required for metrics_optional_domains? Do we need to add a metrics_optional_packages which sets pcp_optional_packages?

Yep, good point - I think that will be needed here.

Done

[richm]

[citest]

[richm]

[citest]

[richm]

@natoscott ok to merge?

[natoscott]

@natoscott ok to merge?

LGTM.