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CEL 表达式

CEL 表达式​

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Kubernetes 中的通用表达式语言 | Kubernetes

通用表达式语言 (Common Expression Language, CEL)  用于声明 Kubernetes API 的验证规则、策略规则和其他限制或条件。

CEL 表达式在  API 服务器中直接进行处理， 这使得 CEL 成为许多可扩展性用例的便捷替代方案，而无需使用类似 Webhook 这种进程外机制。 只要控制平面的 API 服务器组件保持可用状态，你的 CEL 表达式就会继续执行。

基本语法​

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语法​

The grammar of CEL is defined below, using | for alternatives, [] for optional, {} for repeated, and () for grouping.

Expr           = ConditionalOr ["?" ConditionalOr ":" Expr] ;
ConditionalOr  = [ConditionalOr "||"] ConditionalAnd ;
ConditionalAnd = [ConditionalAnd "&&"] Relation ;
Relation       = [Relation Relop] Addition ;
Relop          = "<" | "<=" | ">=" | ">" | "==" | "!=" | "in" ;
Addition       = [Addition ("+" | "-")] Multiplication ;
Multiplication = [Multiplication ("*" | "/" | "%")] Unary ;
Unary          = Member
               | "!" {"!"} Member
               | "-" {"-"} Member
               ;
Member         = Primary
               | Member "." IDENT ["(" [ExprList] ")"]
               | Member "[" Expr "]"
               ;
Primary        = ["."] IDENT ["(" [ExprList] ")"]
               | "(" Expr ")"
               | "[" [ExprList] [","] "]"
               | "{" [MapInits] [","] "}"
               | ["."] IDENT { "." IDENT } "{" [FieldInits] [","] "}"
               | LITERAL
               ;
ExprList       = Expr {"," Expr} ;
FieldInits     = IDENT ":" Expr {"," IDENT ":" Expr} ;
MapInits       = Expr ":" Expr {"," Expr ":" Expr} ;

数值类型​

Values in CEL represent any of the following:

| Type | Description | | -------- | ---------------------------------- | | int | 64-bit signed integers | | uint | 64-bit unsigned integers | | double | 64-bit IEEE floating-point numbers |

Kwok 中的应用​

在 Kwok 中，如果希望自定义 Pod/Node Metrics 模拟，就需要用到 CEL 表达式。

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ResourceUsage | KWOK

With CEL expressions, it is even possible to simulate resource usages dynamically. For example, the following expression yields memory usage that grows linearly with time.

expression: 'Quantity("1Mi") * (pod.SinceSecond() / 60.0)'

Please refer to CEL expressions in kwok for an exhausted list that may be helpful to configure dynamic resource usage.

Kwok CEL 存在的问题​

实际使用发现，Kwok 的 CEL 表达式计算有一些问题，实际上还不可用。提了两个相关的 Issue：