capistrano，：db角色，目的是什么？ [英] capistrano, :db role, what's it for?

问题描述

据我所知，capistrano ：db 角色仅用于运行迁移。

As far as I can tell, the capistrano :db role is used only to run migrations.

（因此，在大多数情况下，不应实际上是运行数据库的服务器。为什么会有ruby / rails在那里堆叠（或允许ssh登录）？这就是您要实际执行rails迁移的任何服务器）。

(Thus, in most cases it probably shouldn't actually be the server that runs your database. Why would you have a ruby/rails stack there (or allow ssh logins there)? it's just whatever server you want to actually execute the rails migrations).

只有标识为的数据库角色的服务器：primary => true 用于运行迁移。

And only the server identified as db role with :primary => true is used to run migrations.

因此，任何其他服务器被标识为 db角色，但没有：primary =>真的 ...什么都没用？那么，为什么 capify创建的默认deploy.rb鼓励您列出它们呢？？您甚至会在这里列出什么？

So any other servers identified as 'db' role but without :primary => true... are used for nothing at all? So why does the default deploy.rb created by capify . encourage you to list them? What would you even list here?

我丢失了什么？

推荐答案

显然，角色：db 的名称具有误导性。正如您所指出的，Capistrano将其定义为主机（使用：primary => true ）作为我们执行 rake db：migrate ，但是数据库服务器并非始终在此类主机上运行。我们可以通过Rails应用程序更改远程数据库服务器的架构。此类主机的正确角色名称不是：db 。

Obviously, the name of role :db is misleading. As you pointed out, Capistrano defines it (with :primary => true) as a host that we execute rake db:migrate on, but database servers are not always running on such hosts. We can alter the schema of remote database server through a Rails app. The correct role name for this kind of host is not :db.

从 lib / capistrano / configuration / roles.rb ，原始角色：db 的含义是运行数据库服务器的主机。我们应该登录到：db 主机并执行一些任务。

Inferring from the comments on lib/capistrano/configuration/roles.rb, the original meaning of the role :db is a host on which database servers are running. We are expected to login to the :db hosts and do some tasks.

Capistrano的设计师应该已经定义了：migration 角色或其他用于 deploy：migrate 任务的角色。但是：db 角色与此任务之间的关联是六年前通过 9a6d2fb ，此后一直没有更改。

The designers of Capistrano should have defined :migration role or something else for the deploy:migrate task. But the association between the :db role with this task was defined six years ago with 9a6d2fb and has not been changed since then.

通常，Capistrano的用户可以定义角色并将其与任务关联自由地。 deploy：migrate 任务作为食谱提供给Rails开发人员。不幸的是，此食谱对我们如何进行数据库迁移存在误解，并且已被广泛使用了很长时间。

Generally speaking, the users of Capistrano can define roles and associate them with tasks freely. The deploy:migrate task is provided just as a recipe for Rails developers. Unfortunately, this recipe includes a misconception about how we do the database migration and is used widely for a long time.

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