Docker化Rails应用向同环境Rails服务发起HTTP请求失败

drmanabase ➜ /app (002-build-seed-file ✗) $ ruby -v
ruby 3.1.0p0 (2021-12-25 revision fb4df44d16) [x86_64-linux]
drmanabase ➜ /app (002-build-seed-file ✗) $ rails -v
Rails 7.0.2.3

通过Dockerfile、docker-compose.yml和devcontainer.json搭建了两个Rails/Postgres容器化应用：

• 「public应用」：存放无需保密的业务逻辑；
• 「private应用」：存放需保密的业务逻辑，作为HTTP服务接收请求并返回响应。

private应用的基础Rails结构已搭建完成，本地浏览器访问localhost:3000可正常显示页面，但从public应用容器内执行以下代码发起请求时失败：

require 'net/http'
require 'uri'

uri = URI('http://localhost:3000/')

Net::HTTP.get(uri)

报错信息 #

/usr/local/lib/ruby/3.1.0/socket.rb:1214:in `__connect_nonblock': Failed to open TCP connection to localhost:3000 (Cannot assign requested address - connect(2) for [::1]:3000) (Errno::EADDRNOTAVAIL)
        from /usr/local/lib/ruby/3.1.0/socket.rb:1214:in `connect_nonblock'
        from /usr/local/lib/ruby/3.1.0/socket.rb:56:in `connect_internal'
        from /usr/local/lib/ruby/3.1.0/socket.rb:137:in `connect'
        from /usr/local/lib/ruby/3.1.0/socket.rb:642:in `block in tcp'
        from /usr/local/lib/ruby/3.1.0/socket.rb:227:in `each'
        from /usr/local/lib/ruby/3.1.0/socket.rb:227:in `foreach'
        from /usr/local/lib/ruby/3.1.0/socket.rb:632:in `tcp'
        from /usr/local/lib/ruby/3.1.0/net/http.rb:998:in `connect'
        from /usr/local/lib/ruby/3.1.0/net/http.rb:976:in `do_start'
        from /usr/local/lib/ruby/3.1.0/net/http.rb:965:in `start'
        from /usr/local/lib/ruby/3.1.0/net/http.rb:627:in `start'
        from /usr/local/lib/ruby/3.1.0/net/http.rb:503:in `get_response'
        from /usr/local/lib/ruby/3.1.0/net/http.rb:474:in `get'
        from /app/lib/mtg_json/tempCodeRunnerFile.rb:6:in `<main>'
/usr/local/lib/ruby/3.1.0/socket.rb:1214:in `__connect_nonblock': Cannot assign requested address - connect(2) for [::1]:3000 (Errno::EADDRNOTAVAIL)
        from /usr/local/lib/ruby/3.1.0/socket.rb:1214:in `connect_nonblock'
        from /usr/local/lib/ruby/3.1.0/socket.rb:56:in `connect_internal'
        from /usr/local/lib/ruby/3.1.0/socket.rb:137:in `connect'
        from /usr/local/lib/ruby/3.1.0/socket.rb:642:in `block in tcp'
        from /usr/local/lib/ruby/3.1.0/socket.rb:227:in `each'
        from /usr/local/lib/ruby/3.1.0/socket.rb:227:in `foreach'
        from /usr/local/lib/ruby/3.1.0/socket.rb:632:in `tcp'
        from /usr/local/lib/ruby/3.1.0/net/http.rb:998:in `connect'
        from /usr/local/lib/ruby/3.1.0/net/http.rb:976:in `do_start'
        from /usr/local/lib/ruby/3.1.0/net/http.rb:965:in `start'
        from /usr/local/lib/ruby/3.1.0/net/http.rb:627:in `start'
        from /usr/local/lib/ruby/3.1.0/net/http.rb:503:in `get_response'
        from /usr/local/lib/ruby/3.1.0/net/http.rb:474:in `get'
        from /app/lib/mtg_json/tempCodeRunnerFile.rb:6:in `<main>'

核心原因 #

容器内的localhost指向容器自身，而非宿主机或其他容器。因此public应用容器中请求localhost:3000时，实际是访问自身的3000端口，而非private应用的服务。

具体修复步骤 #

1. 确认网络归属
   确保两个应用处于同一个Docker网络中。默认情况下，docker-compose会为项目创建专属网络，所有服务自动加入；如果是分开的docker-compose配置，需手动指定共享网络。

2. 替换访问地址为服务名
   在public应用的请求代码中，将localhost替换为private应用在docker-compose.yml中定义的服务名。例如private应用的服务名为private-app，修改后的代码如下：

   require 'net/http'
   require 'uri'
   
   uri = URI('http://private-app:3000/')
   
   Net::HTTP.get(uri)
   

3. 确保private应用绑定正确地址
   确认private应用的Rails服务绑定到0.0.0.0（允许所有网卡访问），而非默认的127.0.0.1（仅本地访问）。启动命令需改为：

   rails server -b 0.0.0.0 -p 3000
   

   也可在Dockerfile的CMD指令或docker-compose.yml的command字段中指定该启动命令。

4. 验证网络连通性
   进入public应用容器，执行ping命令测试与private应用的连通性：

   ping private-app
   

   若能ping通则网络配置正常；若不通，检查docker-compose的网络配置是否正确。

内容的提问来源于stack exchange，提问作者Justin Simpson