CEL 表达式
CEL 表达式
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
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。
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：