[CAMEL-19137] Favor CompositeMeterRegistry instances in Camel registry

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.18.3
• Fix Version/s: 3.20.3, 3.21.0, 4.0-M3, 4.0.0
• Component/s: camel-micrometer
• Estimated Complexity: Unknown
• Assignee: Unassigned
• Reporter: Adriano Machado
• Created: 12/Mar/23 22:29
• Updated: 13/Mar/23 06:34
• Resolved: 13/Mar/23 06:33

Description

When Spring Boot detects more than one instance of `MeterRegistry` in the application context configuration (for example, both `meter-registry-jmx` and `meter-registry-prometheus` are on the classpath and the actuator endpoint for Prometheus is enabled), the auto-configuration adds an instance of `CompositeMeterRegistry` and configures it as the primary bean.

When the micrometer component starts, it looks for an instance of `MeterRegistry` on Camel registry with the name `MicrometerConstants.METRICS_REGISTRY_NAME`. If not found, the component tries to locate a single instance of any `MeterRegistry` object on the registry.

In the previous example configuration, there will be 3 instances of `MeterRegistry`, and the current behavior is to create a new instance of `MeterRegistry` to use.

This changes the default behavior to look first for instances of `CompositeMeterRegistry` before looking for instances of `MeterRegistry`.