June 2021
Intermediate to advanced
335 pages
5h 50m
Chinese
Content preview from Kubernetes编程
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224
｜
第
8
章
s.Meta().Context
它同时也允许我们通过
s.Convert
为子类型调用
Scheme
的转换函数，或者不
考虑注册的转换函数直接通过
s.DefaultConvert
进行转换。
在大部分的转换场景，都完全无须指定转换范围。简单起见，你可以完全忽
略它的存在，只有当你遇到了一个复杂的问题，必须要获取源和目标对象的
上下文时再使用它。
8.4.6
默认值处理
默认值处理是
API
生命周期里给对象（来自客户端或者
etcd
）中缺失的字段
填充默认值的步骤。例如，
Pod
有个
restartPolicy
字段。如果用户不指定该值，
该字段将默认填充
Always
。
假设我们在使用一个
2014
年时的旧版本
Kubernetes
。
restartPolicy
字段是
当时最新发布的版本引入到系统中的。在你的集群进行了一次升级后，
etcd
里有个
Pod
对象并没有
restartPolicy
字段。执行
kubectl get pod
将从
etcd
读取到老的
Pod
对象，然后默认值处理代码将会添加默认值
Always
。从
用户的视角来看，老
Pod
突然神奇地有了新的
restartPolicy
字段值。
参考图
8-6
了解现在的
Kubernetes
中，在请求处理流程中默认值处理逻辑发
生的位置。注意默认值处理只会作用于外部类型，而不会作用于内部类型。
现在让我们看一看默认值处理的代码。默认值处理是
k8s.io/apiserver
通过
Scheme
进行初始化的，类似转换。因此，我们也需要在
Scheme
中为我们的
自定义类型注册默认值处理函数。 ...
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