Migration guide to Spring Boot 4 miss metrics export issue.

[michaldo]

In my application metrics are scrapped by Prometheus and spans are exported to Opentelemetry
When I upgraded to Spring Boot 4, metrics started to be exported to Opentelemetry.

It is surprising because https://spring.io/blog/2025/11/18/opentelemetry-with-spring-boot#exporting-metrics says:

To enable it in your application, you have to set the management.otlp.metrics.export.url property, e.g.

management.otlp.metrics.export.url=http://localhost:4318/v1/metrics
With that, Micrometer exports metrics in OTLP format to the backend

It is not true, because export runs automatically
I tamed uncontrolled export by management.defaults.metrics.export.enabled=false. I think this nuance should be included in migration guide

[wilkinsona]

I think it's the blog post that's inaccurate, although I'd like to double-check with @mhalbritter.

You haven't said so in your description, but I would guess that you're using spring-boot-starter-opentelemetry. This, being a starter, is fairly opinionated and is primarily intended for exporting both metrics and traces using OTLP.

If you don't want metrics to be exported over OTLP you could exclude io.micrometer:micrometer-registry-otlp or set management.otlp.metrics.export.enabled=false. Alternatively, you could stop using the starter and declare the specific dependencies that you need instead.

[michaldo]

I think now blog is OK, migration guide is OK but starter is wrong.
Metrics should not be published if metric receiver is not configured

[wilkinsona]

Metrics should not be published if metric receiver is not configured

We disagree there, as do the Micrometer team. The OTLP metrics registry will export to http://localhost:4318/v1/metrics by default. You'll see the same behavior with Spring Boot 3.x if you depend on micrometer-registry-otlp (as you've chosen to do with Spring Boot 4.0 by using the new OpenTelemetry starter).

[michaldo]

I was not aware that common habit for actuator metrics is publishing to localhost.
Considering that it seems to me that blog note is not precise enough

[wilkinsona]

I've updated the blog post. I'll leave this open for now as a reminder to double-check things with @mhalbritter.