[FIXED] Make Spring Boot Actuator aware of X-Forwarded-Prefix header?

Issue

We're using Spring Boot 2.7.0 with spring-boot-starter-actuator that we're exposing on port 8081 under the /management context path. The proxy sets several X-Forwarded-* headers, including the X-Forwarded-Prefix header that is set to /service. But when navigating to https://www.company.com/management this is what is returned:

{
    "_links": {
        "self": {
            "href": "https://www.company.com/management",
            "templated": false
        },
        "beans": {
            "href": "https://www.company.com/management/beans",
            "templated": false
        },
        "caches-cache": {
            "href": "https://www.company.com/management/caches/{cache}",
            "templated": true
        },
        "caches": {
            "href": "https://www.company.com/management/caches",
            "templated": false
        },
        "health": {
            "href": "https://www.company.com/management/health",
            "templated": false
        },
        "health-path": {
            "href": "https://www.company.com/management/health/{*path}",
            "templated": true
        },
        "info": {
            "href": "https://www.company.com/management/info",
            "templated": false
        },
        "conditions": {
            "href": "https://www.company.com/management/conditions",
            "templated": false
        },
        "configprops": {
            "href": "https://www.company.com/management/configprops",
            "templated": false
        },
        "configprops-prefix": {
            "href": "https://www.company.com/management/configprops/{prefix}",
            "templated": true
        },
        "env": {
            "href": "https://www.company.com/management/env",
            "templated": false
        },
        "env-toMatch": {
            "href": "https://www.company.com/management/env/{toMatch}",
            "templated": true
        },
        "integrationgraph": {
            "href": "https://www.company.com/management/integrationgraph",
            "templated": false
        },
        "loggers": {
            "href": "https://www.company.com/management/loggers",
            "templated": false
        },
        "loggers-name": {
            "href": "https://www.company.com/management/loggers/{name}",
            "templated": true
        },
        "heapdump": {
            "href": "https://www.company.com/management/heapdump",
            "templated": false
        },
        "threaddump": {
            "href": "https://www.company.com/management/threaddump",
            "templated": false
        },
        "metrics-requiredMetricName": {
            "href": "https://www.company.com/management/metrics/{requiredMetricName}",
            "templated": true
        },
        "metrics": {
            "href": "https://www.company.com/management/metrics",
            "templated": false
        },
        "scheduledtasks": {
            "href": "https://www.company.com/management/scheduledtasks",
            "templated": false
        },
        "sessions-sessionId": {
            "href": "https://www.company.com/management/sessions/{sessionId}",
            "templated": true
        },
        "sessions": {
            "href": "https://www.company.com/management/sessions",
            "templated": false
        },
        "mappings": {
            "href": "https://www.company.com/management/mappings",
            "templated": false
        },
        "refresh": {
            "href": "https://www.company.com/management/refresh",
            "templated": false
        },
        "features": {
            "href": "https://www.company.com/management/features",
            "templated": false
        },
        "traces": {
            "href": "https://www.company.com/management/traces",
            "templated": false
        }
    }
}

I'm expecting the href's in the response to start with https://www.company.com/service due to the supplied X-Forwarded-Prefix header, but this is not the case. I've tried to add the ForwardedHeaderFilter like this:

@Bean
public FilterRegistrationBean<ForwardedHeaderFilter> forwardedHeaderFilterFilterRegistrationBean() {
    ForwardedHeaderFilter forwardedHeaderFilter = new ForwardedHeaderFilter();
    FilterRegistrationBean<ForwardedHeaderFilter> bean = new FilterRegistrationBean<>(forwardedHeaderFilter);
    bean.setOrder(Ordered.HIGHEST_PRECEDENCE);
    return bean;
}

but it makes no difference.

How can I make actuator take the X-Forwarded-Prefix header into account when generating the links to the endpoints behind a proxy?

Solution

I got the same problem. I found that ManagementContextAutoConfiguration uses separate WebApplicationContext if management port is different. That is why declaring of ForwardedHeaderFilter has no effect. Maybe there is an issue in spring actuator. I made this hack and it seems to be working. But I hope somebody will find better solution.

@Component
@ConditionalOnManagementPort(ManagementPortType.DIFFERENT)
public class ManagementContextFactoryBeanPostProcessor
        implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName)
            throws BeansException {
        if (bean instanceof ManagementContextFactory managementContextFactory) {
            return (ManagementContextFactory) (parent, configurationClasses) -> {
                var context = managementContextFactory.createManagementContext(parent, configurationClasses);
                if (context instanceof GenericWebApplicationContext genericWebApplicationContext) {
                    genericWebApplicationContext.registerBean(ForwardedHeaderFilterRegistrationBean.class);
                }
                return context;
            };
        }
        return BeanPostProcessor.super.postProcessBeforeInitialization(bean, beanName);
    }

    public static class ForwardedHeaderFilterRegistrationBean
            extends FilterRegistrationBean<ForwardedHeaderFilter> {

        public ForwardedHeaderFilterRegistrationBean() {
            setFilter(new ForwardedHeaderFilter());
            setOrder(Ordered.HIGHEST_PRECEDENCE);
        }

    }

}

Answered By - Reeson
Answer Checked By - Gilberto Lyons (JavaFixing Admin)