我无法通过Rails连接到远程mysql服务器

Question

I have a very strange problem. I have a mysql database setup on an amazon ec2 server. I have opened up the amazon firewall and my router firewalls appropriately so I can connect through port 3306. I can connect to the ec2 server easily from my linux VM at the command line as follows:

me@me-VirtualBox:~/host/workspace/rails-apps/sm$ mysql -h redacted.amazonaws.com -u redacted -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 4012389
Server version: 5.5.20 MySQL Community Server (GPL)

Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>

So the connection works. This verifies that I can successfully punch through the firewall, and there is no funny business due to running inside a VM. So now I try it from within ruby as follows

require 'rubygems'
require 'mysql'

mycon = Mysql::new("redacted.amazonaws.com", "redacted", "redacted", "redacted")

symres = mycon.query("select * from symbols where symbol = \"AAPL\";")  

symres.each do |symbol|
  puts symbol[0].to_s
end

mycon.close

This prints out "AAPL" at the command line. So everything is working from the ruby perspective. Now I try connecting using ruby on rails.

development:
  adapter: mysql2
  encoding: utf8
  reconnect: false
  database: redacted
  pool: 5
  username: redacted
  password: redacted
  host: redacted.amazonaws.com 
  port: 3306

So I start up the rails server, using the "rails server" command. WebBRICK starts ok and displays this

me@me-VirtualBox:~/host/workspace/rails-apps/sm$ rails server
=> Booting WEBrick
=> Rails 3.2.7 application starting in development on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
[2012-08-18 10:00:08] INFO  WEBrick 1.3.1
[2012-08-18 10:00:08] INFO  ruby 1.8.7 (2011-06-30) [x86_64-linux]
[2012-08-18 10:00:14] INFO  WEBrick::HTTPServer#start: pid=9977 port=3000

I open up my browser window and connect to

http://localhost:3000 

in Chrome. Chrome spins indefinitely. No message appears in the console window where WebBRICK was started. This is all I see in the rails log:

Started GET "/" for 127.0.0.1 at Sat Aug 18 09:39:47 -0600 2012
Connecting to database specified by database.yml

I leave it alone for 5 minutes and nothing happens. I have to kill WebBRICK with a ctrl-c.

My only clue as to what could be happening is that after webrick is shutdown, I try to connect using mysql as shown above and I get this error:

me@me-VirtualBox:~/host/workspace/rails-apps/sm$ mysql -h redacted.amazonaws.com -u redacted -p
Enter password: 
ERROR 1129 (HY000): Host 'redacted.co.comcast.net' is blocked because of many    connection errors; unblock with 'mysqladmin flush-hosts'

So this is indicating that ruby on rails is failing to connect (probably in a loop with a retry) and the mysql db on the amazon server has detected this and blocked that host from connecting. So I log into the amazon host, run the flush-hosts command, and can connect from the command line or the ruby script. But I can never get rails to connect.

Rails Version: 3.2.7 Ruby Version: 1.8.7 My SQL server version: 5.5.20

Any ideas? I'm at a loss for how to debug what the connection error inside rails could be. I am not getting a stack trace, crash, or anything that could help me debug what is going on .

Answer 1

Try writing a simple ruby script to test the mysql2 gem (it looks like you already tested mysql, but your rails app uses mysql2).

Also, try stepping through the code with ruby-debug or some other debugger.

Answer 2

finally got this stack trace:

it looks like there is an internal error which then causes rails to connect to the database again... causing a deadlock:

ActiveRecord::ConnectionTimeoutError (could not obtain a database connection within 5 seconds (waited 5.40695462 seconds). The max pool size is currently 25; consider increasing it.):
  activerecord (3.2.11) lib/active_record/connection_adapters/abstract/connection_pool.rb:258:in `block (2 levels) in checkout'
  activerecord (3.2.11) lib/active_record/connection_adapters/abstract/connection_pool.rb:242:in `loop'
  activerecord (3.2.11) lib/active_record/connection_adapters/abstract/connection_pool.rb:242:in `block in checkout'
  /home/ubuntu/.rvm/rubies/ruby-1.9.3-p286/lib/ruby/1.9.1/monitor.rb:211:in `mon_synchronize'
  activerecord (3.2.11) lib/active_record/connection_adapters/abstract/connection_pool.rb:239:in `checkout'
  activerecord (3.2.11) lib/active_record/connection_adapters/abstract/connection_pool.rb:102:in `block in connection'
  /home/ubuntu/.rvm/rubies/ruby-1.9.3-p286/lib/ruby/1.9.1/monitor.rb:211:in `mon_synchronize'
  activerecord (3.2.11) lib/active_record/connection_adapters/abstract/connection_pool.rb:101:in `connection'
  activerecord (3.2.11) lib/active_record/connection_adapters/abstract/connection_pool.rb:410:in `retrieve_connection'
  activerecord (3.2.11) lib/active_record/connection_adapters/abstract/connection_specification.rb:171:in `retrieve_connection'
  activerecord (3.2.11) lib/active_record/connection_adapters/abstract/connection_specification.rb:145:in `connection'
  activerecord (3.2.11) lib/active_record/query_cache.rb:67:in `rescue in call'