Merge pull request #627 from killbill/aviate-health-config

aviate health: Add section on runtime properties

Author: pierre

userguide/aviate/aviate-health.adoc

@@ -93,6 +93,22 @@ The metrics exposed by the Aviate plugin can mainly be categorized in the follow
 
 |===
 
+=== Runtime Properties
+
+Properties can be specified to configure the Kill Bill system including its plugins. The following https://docs.killbill.io/latest/userguide_configuration#configuration_properties_table[documentation] shows the main configuration properties.
+
+
+The values for these properties can come from a number of sources and the system will evaluate based on the following order:
+
+* Immutable system properties: Properties set by the Kill Bill system - e.g. `user.timezone` set to `GMT`
+* Tenant configurations: Properties that have been overridden on a per-tenant level
+* Environment variables: Environment variables that have been set using the `KB_org_*` syntax
+* Runtime configurations: Properties that can be specified as a system property using the `-D<propName>=<propValue>` syntax or through a system property file identified by the system property `-Dorg.killbill.server.properties=<propertyFile>`
+* Default property values: Default values if none of the above overrode the default value
+
+This flexibility is offered by default and it allows to adopt different deployment models along with a fine grained granularity at the tenant level. However, to make it easier to understand the runtime values of these properties, we have created the endpoint `/v1/health/config`: It provides the view of what the system is running along with the required information about where each property value comes from.
+
+
 === Queue Metrics
 
 Queue metrics can be used to assess the health of the Kill Bill internal queues.