A request to expose the latest revision and latest committed at of the watcher as metrics

[be-hase]

Hello, I have a feature request for centraldogma.
How about adding the following metrics?

centraldogma_latest_commited_at{project="xxx", repository="xxx", watcher="xxx"} timestamp
centraldogma_latest_revision{project="xxx", repository="xxx", watcher="xxx"} revisionNumber

Motivation:
Having these metrics would allow us to represent changes in centraldogma using Grafana annotations.
Many services use centraldogma as a feature flag system, and being able to visualize changes in Grafana would be highly useful.

[be-hase]

Approach

I am considering the following approach:

First, I will add a module named centraldogma-client-micrometer.
Within this module, I will add a class called WatcherMetrics, which will be executed as follows:

Watcher watcher = ...;
WatcherMetrics.monitor(watcher);

A similar implementation can be found in the following examples:

• ExecutorServiceMetrics
• CaffeineCacheMetrics

Why separate the module?

centraldogma-client does not have a dependency on Micrometer.

Question

Is it possible to retrieve the committed time?
It seems that the Revision class does not include it.

[ikhoon]

centraldogma-client does not have a dependency on Micrometer.

I prefer adding Micrometer dependency to centraldogma-client module because Micrometer is commonly used in Java ecosystem so it may not be an additional dependency in production.

Within this module, I will add a class called WatcherMetrics, which will be executed as follows:

The watch metrics seem useful for most users. What do you think of automatically adding the watcher metrics if a MeterRegistry is registered to ArmeriaCentralDogmaBuilder?

new ArmeriaCentralDogmaBuilder()
   .meterReigistry(meterRegistry, meterIdPrefix)
   // If the prefix is omitted, it defaults to `centraldogma.client`.
   .meterReigistry(meterRegistry)
   .build();

// The watcher exposes metrics if meterRegistry is set until closed.
Watcher watcher = ...;

[ikhoon]

Additionally, it would be perfect if we could integrate MeterRegistry for Spring integration modules.

centraldogma/client/java-spring-boot3-autoconfigure/src/main/java/com/linecorp/centraldogma/client/spring/CentralDogmaClientAutoConfiguration.java

Lines 58 to 63 in 98e0446

	public CentralDogma dogmaClient(
	Environment env,
	CentralDogmaSettings settings,
	Optional<List<CentralDogmaClientFactoryConfigurator>> factoryConfigurators,
	Optional<ArmeriaClientConfigurator> armeriaClientConfigurator,
	Optional<DnsAddressEndpointGroupConfigurator> dnsAddressEndpointGroupConfigurator)

If a MeterRegistry is registered as a bean, the injected bean could be used to create ArmeriaCentralDogma internally.

[be-hase]

Micrometer is commonly used in Java ecosystem so it may not be an additional dependency in production.

I agree.
In fact, centraldogma-client-armeria already has a dependency on Micrometer through Armeria...

What do you think of automatically adding the watcher metrics if a MeterRegistry is registered to ArmeriaCentralDogmaBuilder?

Let's go with that approach. If we want to add more metrics to the Central Dogma client in the future, this structure seems more convenient.

[ikhoon]

If we want to add more metrics to the Central Dogma client in the future

Yes, we are.

[be-hase]

I am considering this approach. What do you think?
#1094