apache Capistrano 部署 rails 应用程序——如何处理长时间的迁移？
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Capistrano to deploy rails application - how to handle long migrations?
提问by Clinton
So I am using Capistrano to deploy a rails application to my production server (apache+passenger) and at the moment deployment usually goes along the lines:
所以我使用 Capistrano 将 Rails 应用程序部署到我的生产服务器（apache+passenger），目前部署通常是这样的：
$cap deploy
$cap deploy:migrations
It got me wondering, let's say my db:migrations took a long time to execute on the production server (a big refactor of the db schema) - in this case what is best practice with Capistrano? What happens if users are connected to my application at the time of deployment? Should I gracefully send users to a static placeholder page while the database is being updated? Does Capistrano handle this automagically? Do I need to code up a recipe to help with this? Or does the internal mechanisms of rails / passenger mean that I don't have to worry at all about this particular case?
这让我想知道，假设我的 db:migrations 在生产服务器上执行需要很长时间（对 db 模式进行了一次重大重构）——在这种情况下，Capistrano 的最佳实践是什么？如果用户在部署时连接到我的应用程序，会发生什么情况？我应该在更新数据库时优雅地将用户发送到静态占位符页面吗？Capistrano 会自动处理吗？我需要编写一个食谱来帮助解决这个问题吗？或者rails/passenger的内部机制是否意味着我完全不必担心这种特殊情况？
Thanks.
谢谢。
回答by John Topley
You should put up a maintenance page if the application is not going to be available for a while. I use this Capistrano task:
如果应用程序暂时不可用，您应该建立一个维护页面。我使用这个 Capistrano 任务：
namespace :deploy do
namespace :web do
desc <<-DESC
Present a maintenance page to visitors. Disables your application's web \
interface by writing a "maintenance.html" file to each web server. The \
servers must be configured to detect the presence of this file, and if \
it is present, always display it instead of performing the request.
By default, the maintenance page will just say the site is down for \
"maintenance", and will be back "shortly", but you can customize the \
page by specifying the REASON and UNTIL environment variables:
$ cap deploy:web:disable \
REASON="a hardware upgrade" \
UNTIL="12pm Central Time"
Further customization will require that you write your own task.
DESC
task :disable, :roles => :web do
require 'erb'
on_rollback { run "rm #{shared_path}/system/maintenance.html" }
reason = ENV['REASON']
deadline = ENV['UNTIL']
template = File.read('app/views/admin/maintenance.html.erb')
page = ERB.new(template).result(binding)
put page, "#{shared_path}/system/maintenance.html", :mode => 0644
end
end
end
The app/views/admin/maintenance.html.erbfile should contain:
该app/views/admin/maintenance.html.erb文件应包含：
<p>We're currently offline for <%= reason ? reason : 'maintenance' %> as of <%= Time.now.utc.strftime('%H:%M %Z') %>.</p>
<p>Sorry for the inconvenience. We'll be back <%= deadline ? "by #{deadline}" : 'shortly' %>.</p>
The final step is to configure the Apache virtual host with some directives to look for the maintenance.htmlfile and redirect all requests to it if it's present:
最后一步是使用一些指令配置 Apache 虚拟主机以查找maintenance.html文件并将所有请求重定向到它（如果存在）：
<IfModule mod_rewrite.c>
RewriteEngine On
# Redirect all requests to the maintenance page if present
RewriteCond %{REQUEST_URI} !\.(css|gif|jpg|png)$
RewriteCond %{DOCUMENT_ROOT}/system/maintenance.html -f
RewriteCond %{SCRIPT_FILENAME} !maintenance.html
RewriteRule ^.*$ /system/maintenance.html [L]
</IfModule>
To put the application into maintenance mode, run cap deploy:web:disableand to make it live again do cap deploy:web:enable.
要将应用程序置于维护模式，请运行cap deploy:web:disable并使其再次生效，请执行以下操作cap deploy:web:enable。
回答by dylanfm
My production deploys generally follow this process:
我的生产部署通常遵循以下过程：
cap production deploy:web:disablewhich directs all requests to a static maintenance pagecap production deploy- migrations etc, testing each of the servers individually to make sure things are OK
cap production deploy:web:enableto make the site work as it should
cap production deploy:web:disable将所有请求定向到静态维护页面cap production deploy- 迁移等，分别测试每个服务器以确保一切正常
cap production deploy:web:enable使网站正常工作
John Topley's response gives you some good in depth info here.
John Topley 的回复在这里为您提供了一些很好的深入信息。
