feat: add metrics_pcp_optional_agents for users to configure optional agents

Feature: PCP provides many agents.  The metrics role will automatically enable
agents for features being managed e.g. the metrics role will automatically
enable the `elasticsearch` agent if `metrics_from_elasticsearch: true`.  The
new parameter `metrics_pcp_optional_agents` allows the user to provide a list
of additional agents to enable.

Reason: Users should be able to enable agents other than the ones for
features managed by the metrics role.

Result: Users can enable the agents they need to use.

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

Author: richm

README.md

@@ -165,6 +165,17 @@ It cannot be used for *removing* policy.
 If you want to remove policy, you will need to use the selinux system
 role directly.
 
+### metrics_pcp_optional_agents: []
+
+List of optional PCP agents to enable.  The role will enable agents for
+components you are managing.  For example, if you use
+metrics_from_elasticsearch, the role will enable the elasticsearch agent
+automatically.  This variable is for additional agents.
+
+```yaml
+metrics_pcp_optional_agents: [dm, nfsclient, openmetrics]
+```
+
 ## Example Playbook
 
 Basic metric recording setup for each managed host only, with one

defaults/main.yml

@@ -57,3 +57,10 @@ metrics_manage_selinux: false
 # performance issues are to be sent.  By default, these events are logged to the
 # local system log only.
 metrics_webhook_endpoint: ''
+
+# List of optional PCP agents to enable.  The role will enable
+# agents for components you are managing.  For example, if you
+# use metrics_from_elasticsearch, the role will enable the
+# elasticsearch agent automatically.  This variable is for
+# additional agents.
+metrics_pcp_optional_agents: []

tasks/main.yml

@@ -117,7 +117,7 @@
     pcp_pmie_endpoint: "{{ metrics_webhook_endpoint }}"
     pcp_pmlogger_discard: "{{ metrics_retention_days }}"
     pcp_target_hosts: "{{ metrics_monitored_hosts }}"
-    pcp_optional_agents: "{{ __metrics_domains }}"
+    pcp_optional_agents: "{{ (__metrics_domains + metrics_pcp_optional_agents) | unique | list }}"
     pcp_accounts: "{{ __metrics_accounts }}"
     pcp_rest_api: "{{ metrics_query_service | bool or
                       metrics_graph_service | bool }}"

tests/tests_verify_fullstack.yml

@@ -7,6 +7,7 @@
     metrics_graph_service: true
     metrics_manage_firewall: true
     metrics_manage_selinux: true
+    metrics_pcp_optional_agents: [dm, nfsclient, openmetrics]
 
   pre_tasks:
     - name: Stop test