Understanding the HTTP 406 Not Acceptable Error in Spring Boot 3 During Prometheus Scraping

Learn how to resolve the `HTTP 406 Not Acceptable` error when integrating Spring Boot 3 with Prometheus for monitoring. Discover the root cause and configure your application effectively.
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Understanding the HTTP 406 Not Acceptable Error in Spring Boot 3 During Prometheus Scraping

If you're running a Spring Boot application and trying to integrate it with Prometheus for performance monitoring, you might encounter an HTTP 406 Not Acceptable error when Prometheus attempts to scrape metrics. This can be frustrating, but by understanding the root cause and applying the right configuration, you can resolve this issue and successfully gather the metrics you need.

The Problem: HTTP 406 Error

When you receive an error like:

[[See Video to Reveal this Text or Code Snippet]]

it indicates that the request made by Prometheus does not align with any of the media types that your Spring Boot application is able to produce. More specifically, this error arises from the Accept header sent in the scraping request, which looks like this:

[[See Video to Reveal this Text or Code Snippet]]

Prometheus is expecting one or more specific formats for the metrics data, and if your application doesn't support these formats, the scraping will fail.

Root Cause Analysis

What Causes the 406 Error?

The 406 Not Acceptable error occurs because:

Media Types Mismatch: The types expected by Prometheus do not match the types your Spring Boot application produces.

Quality Values Range: The quality values (q-values) in the Accept header must be between 0.0 and 1.0 but should align with the responses that your application can generate.

Here’s a breakdown of what each section of the header represents:

application/openmetrics-text;version=1.0.0;q=0.5: Prometheus prefers this format but can downgrade as indicated by the q-values.

text/plain;version=0.0.4;q=0.3: This format is also acceptable but less preferred.

What Can You Do?

If your Spring Boot application does not produce the expected media types, there are a few steps you can take to resolve the issue.

Solution: Configuring Spring Boot for Prometheus Integration

To configure your Spring Boot application correctly and avoid that annoying HTTP 406 Not Acceptable error, consider the following approaches:

1. Ensure Compatible Media Types

First, you should make sure that your Spring Boot application's Actuator is configured to expose metrics in a format that Prometheus expects.

Add OpenMetrics Support: Ensure you're using a library that supports OpenMetrics output.

Here's an example of how to expose metrics in a compatible format:

[[See Video to Reveal this Text or Code Snippet]]

2. Configure Accept Headers

If you want Prometheus to successfully scrape the metrics, it's important that the application can handle the Accept header values.

Modify the Response Types: Ensure that your controllers or Actuator endpoints are set up to handle requests that indicate the expected types, such as application/openmetrics-text.

3. Utilize Appropriate Libraries

Using Spring Boot starters such as spring-boot-starter-actuator can simplify the process. This automatically sets up default responses that are comprehensible by monitoring tools like Prometheus.

4. Testing and Validation

After making the necessary adjustments:

Restart your Spring Boot application.

Initiate Prometheus scraping to confirm that the issue is resolved.

Conclusion

By understanding how to address the HTTP 406 Not Acceptable error with your Spring Boot application during Prometheus scraping, you can ensure robust monitoring of your application’s performance. By following the outlined solutions, you will enhance the compatibility between your Spring Boot APIs and Prometheus eff