有没有什么办法来延迟资源的属性分辨率，直到＆QUOT;执行＆QUOT;相？ [英] Is there any way to delay a resource's attribute resolution until the "execute" phase?

问题描述

我有两个LWRPs。与创建一个磁盘卷，格式化和安装它在虚拟机上的第一个交易，我们会打电话给这个资源 cloud_volume 。第二个资源（不是真正重要的它做什么）需要一个UUID为新格式化的卷这是一个必需的属性，我们会打电话给这个资源 foobar的。

I have two LWRPs. The first deals with creating a disk volume, formatting it, and mounting it on a virtual machine, we'll call this resource cloud_volume. The second resource (not really important what it does) needs a UUID for the newly formatted volume which is a required attribute, we'll call this resource foobar.

资源 cloud_volume 和 foobar的在配方像下面这样被使用。

The resources cloud_volume and foobar are used in a recipe something like the following.

volumes.each do |mount_point, volume|
  cloud_volume "#{mount_point}" do
    size volume['size']
    label volume['label']
    action [:create, :initialize]
  end
  foobar "#{mount_point}" do
    disk_uuid node[:volumes][mount_point][:uuid]   # This is set by cloud_volume
    action [:do_stuff]
  end
end

所以，当我做了厨师来看，我收到了必需的参数disk_identifier丢失！例外。

在做一些挖我发现食谱分两期进行处理，编译阶段和执行阶段后。它看起来像这个问题是在编译的时候，因为这是在时间节点，点[：卷] [装入点] [：UUID] 未设置。

After doing some digging I discovered that recipes are processed in two phases, a compile phase and an execute phase. It looks like the issue is at compile time as that is the point in time that node[:volumes][mount_point][:uuid] is not set.

不幸的是我不能使用OPS code的<一个诀窍href=\"http://web.archive.org/web/20120226074250/http://wiki.ops$c$c.com/display/chef/Evaluate+and+Run+Resources+at+Compile+Time\"相对=nofollow>此处作为cloud_volume LWRP正在使用的通知（所以它会落入文件中所示的反模式）

Unfortunately I can't use the trick that OpsCode has here as notifications are being used in the cloud_volume LWRP (so it would fall into the anti-pattern shown in the documentation)

所以，这一切后，我的问题是，有没有什么办法让周围的 disk_uuid 的值在编译时已知的要求？

So, after all this, my question is, is there any way to get around the requirement that the value of disk_uuid be known at compile time?

推荐答案

一个更清洁的方式是使用的 lazy属性评估。这将评估节点[：卷] [装入点] [：UUID] 在执行期间，而不是编译

A cleaner way would be to use Lazy Attribute Evaluation. This will evaluate node[:volumes][mount_point][:uuid] during execution time instead of compile

foobar "#{mount_point}" do
  disk_uuid lazy { node[:volumes][mount_point][:uuid] }
  action [:do_stuff]
end

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