Heroku 上偶尔出现 Postgres 错误：无法将主机名“<pg URL>”转换为地址：名称或服务未知（PG::Error）答案

【问题标题】：Occasional Postgres error on Heroku: could not translate host name "<pg URL>" to address: Name or service not known (PG::Error)Heroku 上偶尔出现 Postgres 错误：无法将主机名“<pg URL>”转换为地址：名称或服务未知（PG::Error）
【发布时间】：2012-08-23 07:18:15
【问题描述】：

我现在在 Heroku 上使用共享的 postgres（开发/免费）计划，我在日志中看到了相当多的这个错误。连接到 PG 数据库通常可以，所以我不确定这是否在我的控制范围内。 Heroku 状态页面不会列出共享数据库的任何停机时间。

使用 Rails 3.1.1 和 the Unicorn web server。

错误： 无法将主机名“pg60.sharedpg.heroku.com (http://pg60.sharedpg.heroku.com)”转换为地址：名称或服务未知（PG::Error）

我的Unicorn 配置文件（在查看了 Heroku 中 Unicorn 的推荐设置之后）：

worker_processes 3 # amount of unicorn workers to spin up
timeout 30         # restarts workers that hang for 30 seconds
preload_app true

before_fork do |server, worker|
  # Replace with MongoDB or whatever
  if defined?(ActiveRecord::Base)
    ActiveRecord::Base.connection_handler.clear_all_connections!
    ActiveRecord::Base.connection.disconnect!
    Rails.logger.info('Disconnected from ActiveRecord')
  end

  # If you are using Redis but not Resque, change this
  if defined?(Resque)
    Resque.redis.quit
    Rails.logger.info('Disconnected from Redis')
  end
end

after_fork do |server, worker|
  # Replace with MongoDB or whatever
  if defined?(ActiveRecord::Base)
    ActiveRecord::Base.establish_connection
    ActiveRecord::Base.connection_handler.verify_active_connections!
    Rails.logger.info('Connected to ActiveRecord')
  end

  # If you are using Redis but not Resque, change this
  if defined?(Resque)
    Resque.redis = ENV['REDIS_URI']
    Rails.logger.info('Connected to Redis')
  end
end

追踪：

 328 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:1032:in `initialize': could not translate host name "pg60.sharedpg.heroku.com (http://pg60.sharedpg.heroku.com)" to address: Name or service not known (PG::Error)
219 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:1032:in `new'
223 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:1032:in `connect'
225 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:301:in `initialize'
217 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:28:in `new'
235 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:28:in `postgresql_connection'

328 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:1032:in `initialize': could not translate host name "pg60.sharedpg.heroku.com (http://pg60.sharedpg.heroku.com)" to address: Name or service not known (PG::Error)
219 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:1032:in `new'
223 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:1032:in `connect'
225 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:301:in `initialize'
217 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:28:in `new'
235 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/postgresql_adapter.rb:28:in `postgresql_connection'
235 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:304:in `new_connection'
244 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:323:in `checkout_new_connection'
249 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:265:in `block (2 levels) in checkout'
225 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:261:in `loop'
238 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:261:in `block in checkout'
153 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /usr/local/lib/ruby/1.9.1/monitor.rb:201:in `mon_synchronize'
229 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:260:in `checkout'
231 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:162:in `connection'
240 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:409:in `retrieve_connection'
249 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/abstract/connection_specification.rb:107:in `retrieve_connection'
239 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/connection_adapters/abstract/connection_specification.rb:89:in `connection'
194 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.1.1/lib/active_record/base.rb:703:in `table_exists?'
128 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/app.rb:38:in `<top (required)>'
116 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from config.ru:9 (http://config.ru:9):in `require'
124 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from config.ru:9 (http://config.ru:9):in `block in <main>'
179 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.1/lib/rack/builder.rb:51:in `instance_eval'
176 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.1/lib/rack/builder.rb:51:in `initialize'
112 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from config.ru:1 (http://config.ru:1):in `new'
115 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from config.ru:1 (http://config.ru:1):in `<main>'
168 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/unicorn-4.2.0/lib/unicorn.rb:44:in `eval'
180 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/unicorn-4.2.0/lib/unicorn.rb:44:in `block in builder'
181 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/unicorn-4.2.0/lib/unicorn/http_server.rb:691:in `call'
187 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/unicorn-4.2.0/lib/unicorn/http_server.rb:691:in `build_app!'
182 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/unicorn-4.2.0/lib/unicorn/http_server.rb:136:in `start'
178 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/gems/unicorn-4.2.0/bin/unicorn:121:in `<top (required)>'
146 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/bin/unicorn:19:in `load'
148 <13>1 2012-08-27T21:36:37+00:00 d.4122435c-cb44-421a-9a7d-a68bb10457d6 app web.1 (http://web.1) - - from /app/vendor/bundle/ruby/1.9.1/bin/unicorn:19:in `<main>'

【问题讨论】：

如果您解释了您的应用程序的结构可能会有所帮助。应用程序在哪里，它在哪里以及如何托管？它是如何连接到 Herou 的？走哪条路？

标签： ruby-on-rails postgresql heroku unicorn

【解决方案1】：

仅供参考，我遇到了同样的问题（Heroku 遇到了 AWS 问题）。以下是来自客户服务的有用回复 (08/15)：

我们偶尔会在我们的实例上看到 DNS 解析失败，并且我们正在努力通过 AWS 解决这个问题。这个问题真的断断续续，不幸的是，我们很难尝试找出原因。在我们调查期间，我有一个解决方法对于这个问题 - 目前，您正在使用 Django 的默认方式数据库连接 - 它试图建立一个新的连接要求。这是相当昂贵的，这也意味着你需要做为您的每个请求提供 DNS 解析，这将增加非常不幸地面临这个问题的可能性。相反，我建议您使用连接池。你可以找到一些例子这里：

https://devcenter.heroku.com/articles/python-concurrency-and-database-connections

一位客户偶尔（但经常，使用 Django 应用程序）在连接池方面取得了很好的改进，这应该有助于防止它发生。

【讨论】：

【解决方案2】：

这是一个DNS 错误。极不可能与您的代码有任何关系。如果您的 Rails 应用和数据库都在 Heroku 中，请联系 Heroku 支持。

如果您的 Rails 应用程序在 Heroku 云之外运行（搜索“独角兽”一词表明它可能是这样的；请链接到这样的东西；不是每个人都知道什么是“独角兽”），您需要进行一些调试以找出 DNS 问题所在。它是您的应用程序使用的递归 DNS 服务器吗？一些更接近的缓存服务器？一些用于解析 Heroku 的 DNS 的中间服务器（不太可能）？ Heroku的DNS本身？是否是丢包问题，服务器以误报响应的问题，循环集群中的一台坏服务器，......？预计会在dig +trace 和traceroute 或mtr 上花费大量时间——假设您可以在ssh 中使用。如果您有root，tcpdump 和tshark 也可能有用，检查您正在使用的 DNS 服务器的日志（如果您可以访问它们）。

如果您没有 shell 访问权限，那么您几乎必须得到与您托管的人的支持。

【讨论】：

感谢您的详尽回答，并为遗漏一些格式和缺少链接表示歉意。它在 Heroku 云中运行，所以似乎我必须对 Heroku 支持进行错误处理。我正在使用 Zerigo 将我的域定向到我的 heroku 应用程序，因此这可能是相关的。当他们回复我时，我会在这里更新。
跟进：这是一个 DNS 错误。 Heroku 支持已经清除了它。
@ckbhodge 很高兴听到它:-)