When using Spring Boot with Prometheus for monitoring and metrics, you might encounter a situation where Prometheus registers requests with an "UNKNOWN" URI. This happens because, by default, Spring Boot does not provide Prometheus with endpoint information, leading to incomplete monitoring data.
To resolve this issue and obtain accurate endpoint information in Prometheus, we can implement a URI tagging filter. This filter will capture incoming requests, extract their URIs, and tag the Prometheus metrics with the corresponding URIs.
In your Spring Boot application, follow these steps:
-
Create a controller that handles a generic route for various URIs:
@RestController @RequestMapping("/report/odata4") public class TestController { @RequestMapping("/**") @GetMapping @PostMapping public void genericRoute(final HttpServletRequest req, final HttpServletResponse resp) throws IOException { resp.setContentType("text/html"); try (final PrintWriter writer = resp.getWriter()) { writer.println("<html><body>"); writer.println("<h1>Hello, Controller</h1>"); writer.println("</body></html>"); } } }
-
Create a configuration class that registers a UriTaggingFilter as a filter bean. This filter will tag Prometheus metrics with the request URI.
@Configuration public class PrometheusUriFilterConfig { @Bean public FilterRegistrationBean<UriTaggingFilter> uriTaggingFilter(MeterRegistry meterRegistry) { FilterRegistrationBean<UriTaggingFilter> registrationBean = new FilterRegistrationBean<>(); registrationBean.setFilter(new UriTaggingFilter(meterRegistry)); registrationBean.addUrlPatterns("/*"); return registrationBean; } @WebFilter("/*") public static class UriTaggingFilter extends OncePerRequestFilter { private final MeterRegistry meterRegistry; public UriTaggingFilter(MeterRegistry meterRegistry) { this.meterRegistry = meterRegistry; } @Override protected void doFilterInternal( HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException { long startTime = System.currentTimeMillis(); try { filterChain.doFilter(request, response); } finally { long endTime = System.currentTimeMillis(); long requestTime = endTime - startTime; String uri = request.getRequestURI(); Timer.builder("http.server.requests") .tags("uri", uri) .register(meterRegistry) .record(requestTime, TimeUnit.MILLISECONDS); } } } }
With this configuration, your Prometheus metrics will now include accurate endpoint information.
