Spring Boot 2.x example missing

[bu3]

Hi,

I have an existing Spring Boot 2.7.14 application where metrics are collected with Dropwizard.
I don't plan to migrate to MicroMeter in the short term so I cannot use io.micrometer:micrometer-registry-prometheus to enable the Spring provided Prometheus endpoint.

So I've been trying to use:

• io.prometheus:simpleclient_dropwizard:0.16.0
• io.prometheus:simpleclient_spring_boot:0.16.0

it looks like simpleclient_spring_boot is not compatible with Spring boot 2 because it relies on class PublicMetrics that has been deprecated in Spring Boot 2.

Am I looking at the wrong place?
Is it possible to enable the Prometheus Endpoint with Spring Boot 2 in other ways?

Thanks

[fstab]

Hi,

Yes, it is possible to enable the Prometheus endpoint with Spring Boot 2. I think the easiest way is to use the Prometheus MetricsServlet (or PrometheusMetricsServlet in 1.0.x) and register it with your Spring application, something like this:

@Bean
public ServletRegistrationBean createPrometheusServlet() {
    return new ServletRegistrationBean(new MetricsServlet(),"/metrics/*");
}

We are currently working on the preview version of the 1.0.0 releases, so you have two options which MetricsServlet to use:

This is the current release with io.prometheus.client.servlet.jakarta.exporter.MetricsServlet.

<dependency>
    <groupId>io.prometheus</groupId>
    <artifactId>simpleclient_servlet_jakarta</artifactId>
    <version>0.16.0</version>
</dependency>

This is the alpha preview of the upcoming 1.0.0 release with io.prometheus.metrics.exporter.servlet.jakarta.PrometheusMetricsServlet:

<dependency>
    <groupId>io.prometheus</groupId>
    <artifactId>prometheus-metrics-exporter-servlet-jakarta</artifactId>
    <version>1.0.0-alpha-2</version>
</dependency>

The source code of the 1.0.0 version is on the 1.0.x branch.

Here's some context of the current status with Prometheus and Micrometer: I think it would be great if Micrometer used the new Prometheus 1.0.0 library directly. I created a PR for that: micrometer-metrics/micrometer#3987. The PR description has links to a modified Spring Boot version and an example application. If the PR gets accepted we would have the following:

• For most users: Micrometer would automatically support new Prometheus features like Prometheus native histograms. This happens under the hood, no code change required.
• For niche users who need to use Prometheus API directly: If you make the Prometheus registry a compile time dependency rather than a runtime dependency you can use the Prometheus api directly.

Anyway, whether this will happen or not depends on what the Micrometer folks think of this. I will eventually add Spring Boot 2 and Spring Boot 3 examples, but I'll wait a couple of weeks to see what's coming out of the PR discussion, because the examples will depend on whether Micrometer will have direct support for Prometheus Metrics 1.0.0 or not.

[fstab]

In case you are wondering: The goal is to have the 1.0.0 release out before PromCon, which will be 28/29 September 2023.

[bu3]

That's amazing! Thanks for sharing @fstab. I'll give it a try immediately