Zeebe gRPC connection refused with spring-zeebe-starter in Docker Swarm setup

[Ekta]

Hi everyone,

I’m working on a Camunda 8 microservice setup using Spring Boot with spring-zeebe-starter (version 8.5.19) and deploying with Docker Swarm.

Microservices:

• order-service (Spring Boot)
• eureka-server (Spring Boot Eureka for service registry)
• zeebe (custom Zeebe broker image)

Dependency:

<dependency>
  <groupId>io.camunda</groupId>
  <artifactId>spring-zeebe-starter</artifactId>
  <version>8.5.19</version>
</dependency>

Application Properties:

spring.application.name=order
server.port=9093

# Eureka
eureka.client.service-url.defaultZone=http://eureka-server:8761/eureka/
eureka.client.register-with-eureka=true
eureka.client.fetch-registry=true
eureka.instance.prefer-ip-address=true

# Zeebe (gRPC only)
camunda.client.mode=simple
camunda.client.zeebe.gateway-address=zeebe:26500
camunda.client.zeebe.auth.enabled=false
camunda.client.zeebe.plaintext=true
camunda.client.rest.enabled=false
camunda.client.zeebe.maxMetadataSize=32768
camunda.client.zeebe.maxMessageSize=4194304

# OTLP
management.otlp.metrics.export.enabled=false

# Disable other clients
camunda.client.task-client.enabled=false
camunda.client.console.enabled=false
camunda.client.operate.enabled=false
camunda.client.optimize.enabled=false

# Workers
camunda.client.defaults.jobWorker.enabled=true
camunda.client.defaults.jobWorker.stream-enabled=true

# Logging
logging.level.io.camunda=DEBUG
logging.level.io.camunda.zeebe=DEBUG
logging.level.io.camunda.zeebe.spring.client=DEBUG

Docker-compose.yaml

version: '3.8'

services:
  zeebe:
    image: ektahande/zeebe:8.5.19-custom-v9
    container_name: zeebe
    ports:
      - "26500:26500"
    networks:
      - microservices-network

  eureka-server:
    image: ektahande/eureka-server:v12
    container_name: eureka-server
    ports:
      - "8761:8761"
    networks:
      - microservices-network
    healthcheck:
      test: ["CMD", "wget", "--spider", "-q", "http://localhost:8761"]
      interval: 5s
      timeout: 2s
      retries: 20

  order-service:
    image: ektahande/order-service:v17
    container_name: order-service
    ports:
      - "9093:9093"
    environment:
      - EUREKA_CLIENT_SERVICEURL_DEFAULTZONE=http://eureka-server:8761/eureka/
      - CAMUNDA_CLIENT_MODE=simple
      - CAMUNDA_CLIENT_ZEEBE_GATEWAY_ADDRESS=zeebe:26500
      - CAMUNDA_CLIENT_ZEEBE_AUTH_ENABLED=false
      - CAMUNDA_CLIENT_ZEEBE_PLAINTEXT=true
      - MANAGEMENT_OTLP_METRICS_EXPORT_ENABLED=false
      - CAMUNDA_CLIENT_ZEEBE_MAXMETADATASIZE=32768
      - CAMUNDA_CLIENT_ZEEBE_MAXMESSAGESIZE=4194304
    depends_on:
      - zeebe
      - eureka-server
    networks:
      - microservices-network

networks:
  microservices-network:
    driver: overlay

Custom Zeebe image Dockerfile:

FROM camunda/zeebe:8.5.19

COPY zeebe.cfg.yaml /usr/local/zeebe/config/zeebe.cfg.yaml

ENV JAVA_TOOL_OPTIONS="-Dmanagement.otlp.metrics.export.enabled=false"

ENTRYPOINT ["broker"]

zeebe.cfg.yaml:

gateway:
  enable: true
  network:
    host: 0.0.0.0
    port: 26500

broker:
  network:
    host: 0.0.0.0

cluster:
  nodeId: 0
  clusterSize: 1
  replicationFactor: 1
  partitionCount: 1

metrics:
  exporters:
    prometheus:
      enabled: false
    otlp:
      enabled: false

The issue:-
When I start the services, my order-service fails with this error:

Caused by: io.grpc.StatusRuntimeException: UNAVAILABLE: io exception
Caused by: java.net.ConnectException: Connection refused
java.lang.IllegalStateException: Cannot compose rest address from legacy ZeebeClientConfiguration
java.lang.NullPointerException: Cannot invoke "java.util.function.Supplier.get()" because "legacyPropertySupplier" is null

The order-service should connect to Zeebe via gRPC only — no legacy REST fallback.

My Questions:

1. Is my zeebe.cfg.yaml and custom image setup correct for gRPC gateway mode?
2. Do I need to expose any other ports or use a different gateway-address?
3. Why is it trying to compose a REST address when camunda.client.rest.enabled=false?
   4)Is there something missing for Zeebe’s gRPC to be reachable inside the Docker Swarm network?