经过几个小时的研究和试验，我终于弄明白了这一点。
这些问题与我的docker-compose.yml和my_app.conf（Nginx配置）文件中的错误配置有关。

• • 以下是正确的配置**：

将Dockerfile用于Nginx：

FROM nginx:1.18.0
LABEL maintainer="promisepreston@gmail.com"

# Set working directory
WORKDIR /app

# Copy over static assets
COPY public public/

# Copy over entrypoint
COPY docker/entrypoints/nginx-entrypoint.sh /usr/local/bin/nginx-entrypoint.sh

# Copy Nginx config template
RUN rm /etc/nginx/conf.d/default.conf
COPY docker/nginx/my_app.conf /etc/nginx/conf.d/my_app.conf

# Nginx init
RUN ["chmod", "+x", "/usr/local/bin/nginx-entrypoint.sh"]
ENTRYPOINT ["/usr/local/bin/nginx-entrypoint.sh"]

docker-compose.yml文件（包含我的app、database和Nginx配置）：

version: '3'

services:
  app:
    build:
      context: .
      dockerfile: ./docker/${RAILS_ENV}/Dockerfile
    depends_on:
      - database
    expose:
      - "3000"
    restart: always
    volumes:
      - .:/app
      - gem-cache:/usr/local/bundle/gems
      - node-modules:/app/node_modules
    env_file:
      - .env
    environment:
      RAILS_ENV: ${RAILS_ENV}
      RACK_ENV: ${RACK_ENV}

  database:
    image: postgres:12.1
    expose:
      - "5432"
    restart: always
    env_file:
      - .env
    environment:
      POSTGRES_USER: ${DATABASE_USER}
      POSTGRES_PASSWORD: ${DATABASE_PASSWORD}
      POSTGRES_DB: ${DATABASE_NAME}
      POSTGRES_HOST_AUTH_METHOD: ${DATABASE_HOST}
    volumes:
      - postgres-data:/var/lib/postgresql/data
      - ./init.sql:/docker-entrypoint-initdb.d/init.sql
  nginx:
    build:
      context: .
      dockerfile: ./docker/nginx/Dockerfile
    depends_on:
      - app
    ports:
      - "8084:80"
      # - "443:443"
    restart: always
    volumes:
      - .:/app

  volumes:
    gem-cache:
    node-modules:
    postgres-data:

Nginx的my_app.conf文件：

upstream rails_app {
  server app:3000;

}

server {
  listen       80;

  # define your domain
  server_name localhost;

  # define the public application root
  root   /app/public;
  index  index.html index.htm;

  # define where Nginx should write its logs
  access_log /app/log/nginx.access.log;
  error_log /app/log/nginx.error.log;

  # deny requests for files that should never be accessed
  location ~ /\. {
    deny all;
  }

  location ~* ^.+\.(rb|log)$ {
    deny all;
  }

  # serve static (compiled) assets directly if they exist (for rails production)
  location ~ ^/(assets|images|javascripts|stylesheets|swfs|system)/ {
    try_files $uri @rails;

    access_log off;
    gzip_static on; # to serve pre-gzipped version

    expires max;
    add_header Cache-Control public;

    # Some browsers still send conditional-GET requests if there's a
    # Last-Modified header or an ETag header even if they haven't
    # reached the expiry date sent in the Expires header.
    add_header Last-Modified "";
    add_header ETag "";
    break;
  }

  # send non-static file requests to the app server
  location / {
    try_files $uri @rails;
  }

  location @rails {
    proxy_pass        http://rails_app;
    proxy_redirect    off;
    proxy_set_header  Host $http_host;
    proxy_set_header  X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header  X-Real-IP  $remote_addr;

  }

  # redirect server error pages to the static page /50x.html
  error_page   500 502 503 504  /50x.html;
  location = /50x.html {
      root   /app/public;
  }
}

Nginx的nginx-entrypoint.sh文件：

#!/bin/sh

set -e

# Allow nginx to stay in the foreground
# so that Docker can track the process properly
nginx -g 'daemon off;'

• • 注**：

1.我使用了RAILS_ENV、RACK_ENV等变量，您可能不需要这些变量。
1.此外，我的Nginx的WORKDIR是/app，因此在docker-compose.yml文件中将其指定为Nginx配置下的卷非常重要，就像我所做的那样。
1.我将NginxMap到主机上的端口8084，您可以自由地将其Map到主机上的任何可用端口。
就这样。
"我希望这能帮上忙"