spring-cloud-sleuth: o.s.c.s.a.z.ZipkinAutoConfiguration : Check result of the [WebClientSender{https://my-zipkin:443/api/v2/spans}] contains an error [CheckResult{ok=false, error=java.util.concurrent.TimeoutException: WebClientSender{https://my-zipkin:443/api/v2/spans} check() timed out after 1000ms}]

Hello Spring Cloud Sleuth Team,

I am reaching out because I am observing a string issue, hence would like to report it.

Setup: The application is a Spring Boot 2.6.4 + Jubilee 2021.0.1 We have another Zipkin server running fine, in my example, I call it https://my-zipkin:443 Here is my pom for the sleuth/zipkin part:

   <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.4</version>
        <relativePath/>
    </parent>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>2021.0.1</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-cassandra-reactive</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-security</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-kubernetes-fabric8</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-config-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-sleuth</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-sleuth-zipkin</artifactId>
        </dependency>
        <dependency>
            <groupId>io.projectreactor.netty</groupId>
            <artifactId>reactor-netty-http-brave</artifactId>
        </dependency>
        <dependency>
            <groupId>io.micrometer</groupId>
            <artifactId>micrometer-registry-prometheus</artifactId>
        </dependency>
        <dependency>
            <groupId>io.github.resilience4j</groupId>
            <artifactId>resilience4j-micrometer</artifactId>
        </dependency>
        <dependency>
            <groupId>io.github.resilience4j</groupId>
            <artifactId>resilience4j-reactor</artifactId>
        </dependency>
        <dependency>
            <groupId>io.github.resilience4j</groupId>
            <artifactId>resilience4j-spring-boot2</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-contract-verifier</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-core</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.lmax</groupId>
            <artifactId>disruptor</artifactId>
            <version>3.4.4</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.statemachine</groupId>
            <artifactId>spring-statemachine-core</artifactId>
            <version>3.0.1</version>
        </dependency>
        <dependency>
            <groupId>net.logstash.logback</groupId>
            <artifactId>logstash-logback-encoder</artifactId>
            <version>7.0.1</version>
        </dependency>
        <dependency>
            <groupId>de.codecentric</groupId>
            <artifactId>spring-boot-admin-starter-client</artifactId>
            <version>2.6.2</version>
        </dependency>
        <dependency>
            <groupId>org.springdoc</groupId>
            <artifactId>springdoc-openapi-webflux-ui</artifactId>
            <version>1.6.6</version>
        </dependency>
    </dependencies>

Reproducible 100%, on each application startup, I am seeing:

2022-03-05 12:16:35.477 WARN [myservice,,] 10 --- [ main] o.s.c.s.a.z.ZipkinAutoConfiguration : Check result of the [WebClientSender{https://my-zipkin:443/api/v2/spans}] contains an error [CheckResult{ok=false, error=java.util.concurrent.TimeoutException: WebClientSender{https://zmy-zipkin:443/api/v2/spans} check() timed out after 1000ms}] 

The thing is, I am monitoring the Zipkin server in parallel, and it is up and running fine! Other non Spring Boot application connects to it fine during the same time stamp, etc.

What is also strange is later with the same app (the one having the warning) I do receive requests, and I am able to search the traces in the Zipkin server, proof it successfully connected to Zipkin Server, as I am able to see the full traces.

Therefore, I would like to report this issue, not understanding what is going in there. Why is there a time out where apparently, server is working fine, and client is able to send traces to it?

Is there a way to increase this time out from 1000ms to something a bit higher?

Thank you