Spring-boot: MetricsFilter may create an unbounded number of metrics for requests with a templated URI that are not handled by Spring MVC

[heroicefforts]

The MetricsFilter is unsuitable for REST microservices that are backing a large number of entities. In our case, it was trying to generate gauges and counters for /widget/1 to /widget/60000000. It eventually soaks the heap and causes the server to slow to a crawl as it spends most of its CPU cycles in GC. There should be a big red "caveat" bubble in the documentation that details this scenario.

Ideally, a Spring MVC controller metrics controller should be implemented that works similar to the DropWizard Jersey 2 implementation (plus some RequestMapping introspection), then the MetricsFilter could be disabled by default.

[wilkinsona]

The behaviour you've described isn't intended, and it doesn't match what's tested.

In one of the tests there's a request mapping like this: @RequestMapping("templateVarTest/{someVariable}"). It's called with /templateVarTest/foo which results in status.200.templateVarTest.someVariable and response.templateVarTest.someVariable being updated. As you can see, it's the name of the variable in the request mapping rather than the value in the request URI that's used.

Can you please provide a sample or testcase that illustrates the behaviour you have described?

[heroicefforts]

Then, perhaps, it is a consequence of using Jersey with SpringBoot (don't get me started on why we're using both...):

@GET
@Path("/parent/{pid}/child/{cid}")
@Produces("application/json")
@Timed(name="child.reads")
public Response readChild(@Context UriInfo uriInfo, @PathParam("pid") String parentId,
        @PathParam("cid") String childId) { ... } 

[wilkinsona]

Thanks. That'll be it. We need to use Jersey's equivalent of Spring MVC's best matching pattern attribute (assuming it has such a thing).

[beckje01]

So does that mean https://github.com/spring-projects/spring-boot/blob/master/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/autoconfigure/MetricsFilter.java#L104 needs to become pluggable?

[wilkinsona]

@beckje01 No, I don't think so. It think it's something similar to this that we need to do for Jersey.

[beckje01]

Ok so we just need to make sure things are putting that attribute in, this same issue effect Grails 3 as well. So that way anything built on boot the metrics will work for assuming the attribute is set.

[jbellmann]

Hi,
maybe this snippet could help here?

[pdavidson]

I just ran into this with jersey as well. It didn't saturate our jvm. Just filled up 380GB on our graphite server. I'm disabling the filter using:

endpoints:
  metrics:
    filter:
      enabled: false

[wilkinsona]

Adding the following bean to an application will correct the metrics for requests handled by Jersey:

@Bean
public ResourceConfigCustomizer bestMatchingPatternResourceConfigCustomizer(
        final JerseyProperties jerseyProperties) {
    return new ResourceConfigCustomizer() {

        @Override
        public void customize(ResourceConfig config) {
            String applicationPath = determineApplicationPath(jerseyProperties,
                    config);
            config.register(new BestMatchingPatternContainerRequestFilter(
                    applicationPath));
        }

        private String determineApplicationPath(JerseyProperties jerseyProperties,
                ResourceConfig config) {
            if (StringUtils.hasText(jerseyProperties.getApplicationPath())) {
                return jerseyProperties.getApplicationPath();
            }
            ApplicationPath applicationPath = AnnotationUtils
                    .findAnnotation(config.getClass(), ApplicationPath.class);
            return applicationPath == null ? "" : applicationPath.value();
        }

    };

}

/**
 * A {@link ContainerRequestFilter} that sets the
 * {@link HandlerMapping#BEST_MATCHING_PATTERN_ATTRIBUTE} request attribute.
 */
private static final class BestMatchingPatternContainerRequestFilter
        implements ContainerRequestFilter {

    private final String applicationPath;

    private BestMatchingPatternContainerRequestFilter(String applicationPath) {
        this.applicationPath = applicationPath.startsWith("/") ? applicationPath
                : "/" + applicationPath;
    }

    @Override
    public void filter(ContainerRequestContext requestContext)
            throws IOException {
        String matchingPattern = extractMatchingPattern(requestContext);
        requestContext.setProperty(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE,
                matchingPattern);
    }

    private String extractMatchingPattern(
            ContainerRequestContext requestContext) {
        ExtendedUriInfo extendedUriInfo = (ExtendedUriInfo) requestContext
                .getUriInfo();
        List<String> templates = new ArrayList<String>();
        for (UriTemplate matchedTemplate : extendedUriInfo
                .getMatchedTemplates()) {
            String template = matchedTemplate.getTemplate();
            templates.add(template.startsWith("/") ? template : "/" + template);
        }
        if (StringUtils.hasText(this.applicationPath)) {
            templates.add(this.applicationPath);
        }
        Collections.reverse(templates);
        return StringUtils.collectionToDelimitedString(templates, "");
    }

}

Some caveats:

• I don't like that it uses Spring MVC's request attribute (see #7505)
• Regular expressions in @Path don't work particularly well (see #7503)

[soldierkam]

The same happens for almost every HttpServlet used in Spring Boot application. MetricsFilter should create new keys only if it knows what mapping was used.

[r0nin]

@wilkinsona Just as a comment. I used this bean and it indeed solved the problem, but i got strange gauge metrics a la gauge.response..v1.controllerName.apiEndPoint, because the Jersey application path is /, the Controller has a @Path("/controllerName") and the method has a @Path("apiEndPoint").

The problem is probably on our side since the /controllerName might be slightly incorrect, but anyway in the returned concatenation of matching templates this leads to //v1/controllerName/apiEndPoint which obviously causing the .. part in the gauge metric. So to be safe against that, I simply replaced // by / before returning the result.

[deki]

The title of this issue should be changed as this also affects Apache CXF and other frameworks.

[wilkinsona]

The planned move to Micrometer-based metrics will get rid of the metrics filter.

[wilkinsona]

We've decided to align 1.5.x with 2.0's current behaviour and fallback to unmapped when we can't get the best matching pattern from Spring MVC. This will avoid requests that aren't handled by Spring MVC from causing a potentially unbounded number of metrics to be created.

[deki]

Great improvement for those who still stick to that version. Thanks!