Automatically create metrics for caches that are created on-the-fly

[joshiste]

Currently the CacheMetricsRegistrarConfiguration binds the meters for the cache related metrics in a @PostContstruct for all known cache names.

Looking at the spring-boot-sample-cache project and the various caches implementations, most of them don't provide the cache names at this moment and therefore no metrics are provided for these.

[snicoll]

The description of this issue is what is advertized in the documentation.

most of them don't provide the cache names at this moment

The cache name is a mandatory argument for a cache so I am not sure I understand what you are reporting.

[joshiste]

Ok missed that in the docs.
But I wonder if things can be improved?

And also spring-boot-sample-cache should make use of the CacheMetricsRegistrar option (which it currently doesn't). I'd volunteer for a PR on that.

[snicoll]

I don't see how things can be improved at the moment. This was documented after investigating how we could make it better. If you find a way, I am more than happy to review a PR.

As for the cache sample, I still don't understand what you mean, sorry. Not all caches are supported by micrometer so that might be the reason why you don't see metrics. If you have more questions, please ask on StackOverflow or come chat with us on Gitter.

[tkvangorder]

@snicoll I ran into this same issue and had some ideas on how to handle it. I am willing to put a PR forward, but I am looking for guidance on which approach:

The current auto-configuration for cache metrics will only bind caches that are known at start-up. This means that in the case where developers are using @Cacheable, any cache that is created "on-the-fly" will not have its metrics bound to the MeterRegistry.

This is surprising behavior and it seems reasonable to expect all caches, dynamic or otherwise, to have their metrics exposed through micrometer.

This is actually a tricky problem because each CacheManager implementation must be meter-aware. Specifically, a cache should be bound to the registry when CacheManager.getCache(String name) is called. The best place to do this would be in the AbstractCacheManager (in the core Spring Framework), however, the CacheMetricsRegistrar (used to bind a cache to the MeterRegistry) is in the Spring Boot Actuator project.

I can think of two ways to make this work correctly, such that when the actuator library is added to the classpath all caches have their metrics bound to the MeterRegistry :

• Publish a CacheCreatedEvent from within AbstractCacheManager. Given the internals of the registrar, this event would have to have both the cache name and the cache manager from which it was created. This would allow a listener to be defined in the actuator library to wire up each cache to the meter registry. This approach would also mean that it is no longer necessary to have a @PostConstruct method in the CacheMetricsRegistrarConfiguration to bind known caches on startup, as all caches would trigger a call to getCache. This approach would mean changes to both the core Spring library's Cache and then changes to Spring Boot's actuator.

• Create an Aspect that is bound to CacheManager.getCache(String name). This aspect will use the Registrar to bind the cache to the MeterRegistry. This approach also makes it unnecessary to have a separate @PostConstruct to register known caches and will only require changes in the actuator library.

[philwebb]

I personally prefer to avoid aspects when at all possible, but the event idea sounds quite nice to me.

[snicoll]

I like the idea of the event. Please, create an issue in the framework issue tracker and I'll give that a try.

[tkvangorder]

@snicoll I have created that issue here: https://jira.spring.io/browse/SPR-17350

Thanks for looking into it and please feel free to ping me with any questions.