Discourse server 启动失败，出现redis相关的错误答案

【问题标题】：Discourse server fails to start with errors related to redisDiscourse server 启动失败，出现redis相关的错误
【发布时间】：2018-01-17 10:11:12
【问题描述】：

Rails 服务器无法在 Discourse 项目中启动，无论是开发还是生产。以下是尝试以开发模式启动服务器时的日志。该应用程序已安装并一直在工作，它以生产模式部署在 AWS 上，重新启动 unicorn 会加载应用程序一段时间，并且 url 会停止响应并显示错误消息。

来自 $rails s 的开发日志

rb t@ip-XXX-XX-XX-XX-app:/var/www/discourse# vi 
config/environments/development.r
root@ip-172-31-25-46-app:/var/www/discourse# rails s
=> Booting Puma
=> Rails 5.1.4 application starting in production 
=> Run `rails server -h` for more startup options
Exiting
bundler: failed to load command: script/rails (script/rails)
Redis::CommandError: ERR Error running script (call to f_b06356ba4628144e123b652c99605b873107c9be): @user_script:14: @user_script: 14: -MISCONF Redis is configured to save RDB snapshots, but is currently not able to persist on disk. Commands that may modify the data set are disabled. Please check Redis logs for details about the error.   
/var/www/discourse/vendor/bundle/ruby/2.4.0/gems/redis-3.3.5/lib/redis/client.rb:121:in `call'
/var/www/discourse/vendor/bundle/ruby/2.4.0/gems/redis-3.3.5/lib/redis.rb:2399:in `block in _eval'
/var/www/discourse/vendor/bundle/ruby/2.4.0/gems/redis-3.3.5/lib/redis.rb:58:in `block in synchronize'
/usr/local/lib/ruby/2.4.0/monitor.rb:214:in `mon_synchronize'
/var/www/discourse/vendor/bundle/ruby/2.4.0/gems/redis-3.3.5/lib/redis.rb:58:in `synchronize'
/var/www/discourse/vendor/bundle/ruby/2.4.0/gems/redis-3.3.5/lib/redis.rb:2398:in `_eval'
/var/www/discourse/vendor/bundle/ruby/2.4.0/gems/redis-3.3.5/lib/redis.rb:2450:in `evalsha'
/var/www/discourse/vendor/bundle/ruby/2.4.0/gems/message_bus-2.1.1/lib/message_bus/backends/redis.rb:380:in `cached_eval'
/var/www/discourse/vendor/bundle/ruby/2.4.0/gems/message_bus-2.1.1/lib/message_bus/backends/redis.rb:140:in `publish'
/var/www/discourse/vendor/bundle/ruby/2.4.0/gems/message_bus-2.1.1/lib/message_bus.rb:248:in `publish'
/var/www/discourse/lib/distributed_cache.rb:72:in `publish'

**生产日志**

/var/www/discourse/lib/demon/base.rb:109:in `ensure_running'
            /var/www/discourse/lib/demon/base.rb:34:in `block in ensure_running'
            /var/www/discourse/lib/demon/base.rb:33:in `each'
            /var/www/discourse/lib/demon/base.rb:33:in `ensure_running'
            config/unicorn.conf.rb:145:in `master_sleep'
            /var/www/discourse/vendor/bundle/ruby/2.3.0/gems/unicorn-5.1.0/lib/unicorn/http_server.rb:284:in `join'
            /var/www/discourse/vendor/bundle/ruby/2.3.0/gems/unicorn-5.1.0/bin/unicorn:126:in `<top (required)>'
            /var/www/discourse/vendor/bundle/ruby/2.3.0/bin/unicorn:23:in `load'
            /var/www/discourse/vendor/bundle/ruby/2.3.0/bin/unicorn:23:in `<main>'
            E, [2018-01-04T08:43:37.949928 #60] ERROR -- : reaped #<Process::Status: pid 5870 exit 1> worker=unknown
            Detected dead worker 5870, restarting...
            Loading Sidekiq in process id 5883
            Failed to report error: MISCONF Redis is configured to save RDB snapshots, but is currently not able to persist on disk. Commands that may modify the data set are disabled. Please check Redis logs for details about the error. 4 Redis::CommandError (MISCONF Redis is configured to save RDB snapshots, but is currently not able to persist on disk. Commands that may modify the data set are disabled. Please check Redis logs for details about the error.)
            /var/www/discourse/vendor/bundle/ruby/2.3.0/gems/redis-3.3.0/lib/redis/client.rb:121:in `call' web-exception

Redis 日志

   47:M 17 Jan 09:38:01.070 # Can't save in background: fork: Cannot allocate memory
   47:M 17 Jan 09:38:07.087 * 10000 changes in 60 seconds. Saving...

【问题讨论】：

标签： ruby-on-rails redis ruby-on-rails-5 unicorn discourse

【解决方案1】：

问题已解决，编辑此文件

/etc/sysctl.conf 并在最后添加一行

   vm.overcommit_memory=1

在此之后重新启动 sysctl。

  $ sudo sysctl -p /etc/sysctl.conf

Redis 不需要操作系统认为的内存量，状态 1 表示总是过度使用，从不检查。更多详情请关注Redis Docs。

【讨论】：