我有以下docker-compose.yaml

version: '3'
services:
  webapp:
    image: example/webapp
    build:
      context: app
    restart: always
    ports:
      - ":8181"
    deploy:
      replicas: 3
    volumes:
      - secret-store:/app/data
    env_file:
      - .env
    networks:
      - bridged_network
  nginx:
    image: example/reverseproxy
    build:
      context: reverseproxy
    ports:
      - "8181:80"
    depends_on:
      - webapp
networks:
  bridged_network:
    driver: bridge
volumes:
  secret-store:

字符串
nginx映像的构建过程如下

FROM nginx:latest
RUN rm /etc/nginx/conf.d/*
COPY nginx.conf /etc/nginx/conf.d/default.conf

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其中nginx.conf

server {
  listen 80;
  location / {
    proxy_pass http://webapp:8181;
  }
}

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但是在nginx容器日志中：

nginx: [emerg] host not found in upstream "webapp" in /etc/nginx/conf.d/default.conf:6

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为什么nginx无法发现webapp服务？