Zipkin not working in Docker - conncection refused

Question

Zipkin works well locally but not in docker container. All the microservices are registered well in the Eureka and they can communicate well. But the only problem is Zipkin. I am getting the following error:

org.springframework.web.client.ResourceAccessException: I/O error on POST request for "http://localhost:9411/api/v2/spans": Connect to http://localhost:9411 [localhost/127.0.0.1] failed: Connection refused

my docker-compose.yaml is as follows:

version: '3.8'

services:
  currency-exchange:
    image: samankt/springboot-udemy-currency-exchange:0.0.1-SNAPSHOT
    mem_limit: 512m
    ports:
      - '8000:8000'
    networks:
      - saman-network  
    environment:
      EUREKA.CLIENT.SERVICE-URL.DEFAULTZONE: http://naming-server:8761/eureka
      EUREKA.INSTANCE.PREFERIPADDRESS: true  
      SPRING.ZIPKIN.BASE-URL: http://zipkin-server:9411/
      RABBIT_URI: amqp://guest:guest@rabbitmq:5672
      SPRING_RABBITMQ_HOST: rabbitmq
      SPRING_ZIPKIN_SENDER_TYPE: rabbit
    depends_on:
      - naming-server
      - rabbitmq
      
  api-gateway:
    image: samankt/springboot-udemy-currency-api-gateway:0.0.1-snapshot
    mem_limit: 512m
    ports:
      - '8765:8765'
    networks:
      - saman-network  
    environment:
      EUREKA.CLIENT.SERVICE-URL.DEFAULTZONE: http://naming-server:8761/eureka
      EUREKA.INSTANCE.PREFERIPADDRESS: true  
      SPRING.ZIPKIN.BASE-URL: http://zipkin-server:9411/
      RABBIT_URI: amqp://guest:guest@rabbitmq:5672
      SPRING_RABBITMQ_HOST: rabbitmq
      SPRING_ZIPKIN_SENDER_TYPE: rabbit 
    depends_on:
      - naming-server
      - rabbitmq
      
  currency-converter:
    image: samankt/currency-conversion:0.0.1-SNAPSHOT
    mem_limit: 700m
    ports:
      - '8100:8100'
    networks:
      - saman-network  
    environment:
      EUREKA.CLIENT.SERVICE-URL.DEFAULTZONE: http://naming-server:8761/eureka
      EUREKA.INSTANCE.PREFERIPADDRESS: true  
      SPRING.ZIPKIN.BASE-URL: http://zipkin-server:9411/
      SPRING.ZIPKIN.DISCOVERYCLIENTENABLED: true 
      RABBIT_URI: amqp://guest:guest@rabbitmq:5672
      SPRING_RABBITMQ_HOST: rabbitmq
      SPRING_ZIPKIN_SENDER_TYPE: rabbit     
    depends_on:
      - naming-server
      - rabbitmq
      
  naming-server:
    image: samankt/naming-server:0.0.1-SNAPSHOT
    mem_limit: 512m
    ports:
      - '8761:8761'
    environment:
      SPRING.ZIPKIN.BASE-URL: http://zipkin-server:9411/    
    networks:
      - saman-network
      
  zipkin-server:
    image: openzipkin/zipkin:latest
    mem_limit: 400m
    ports:
      - '9411:9411'
    networks:
      - saman-network   
    environment:
      RABBIT_URI: amqp://guest:guest@rabbitmq:5672
    depends_on:
      - rabbitmq
    restart: always
      
      
  rabbitmq:
    image: rabbitmq:3.8.12-management
    ports:
      - '5672:5672'
      - '15672:15672'
    networks:
      - saman-network
    
networks: 
  saman-network:

Answer 1

SOLUTION 1

The error is telling you that the connection on http://localhost:9411/api/v2/spans is refused. When you run your application inside a docker container you need to send the request not with localhost, but through the docker network (in your case saman-network). To access the docker container which runs zipkin you need to send the request to http://zipkin-server:9411/api/v2/spans.

From Spring Boot 3 Sleuth is deprecated and you will need to use micrometer. To use tracing with zipkin you can add the following 4 dependencies to you pom.xml file

<dependency>
     <groupId>io.micrometer</groupId>
     <artifactId>micrometer-tracing-bridge-brave</artifactId>
</dependency>
<dependency>
    <groupId>io.micrometer</groupId>
    <artifactId>micrometer-observation-test</artifactId>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>io.zipkin.reporter2</groupId>
    <artifactId>zipkin-reporter-brave</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

Finally to change the Zipkin endpoint to send the tracing information you need to add the following to your application.yaml file.

management:
  tracing:
    sampling:
      probability: 1.0 # only for testing purpose, switch back to 0.1 for production code
  zipkin:
    tracing:
      endpoint: http://localhost:9411/api/v2/spans

It is good practice to use Spring profiles, therefore you copy your application.yaml file and name it application-docker.yaml. In this new file you can modify the Zipkin endpoint with the zipkin container name zipkin-server.

management:
  tracing:
    sampling:
      probability: 1.0 # only for testing purpose, switch back to 0.1 for production code
  zipkin:
    tracing:
      endpoint: http://zipkin-server:9411/api/v2/spans

You can activate the Spring profiles passing SPRING_PROFILES_ACTIVATE=docker in the environment.

---

SOLUTION 2

For you this solution is faster to implement but I didn't test it. You pass the Zipkin url as an environment value SPRING.ZIPKIN.BASE-URL inside the docker-compose.yml. This property was used with the Sleuth package. With Spring Boot 3 and micrometer try to pass instead: MANAGEMENT.ZIPKIN.TRACING.ENDPOINT: http://zipkin-server:9411/api/v2/spans