Docker Swarm代码分析笔记（14）——strategy

Docker Swarm manage命令的flStrategy选项用来指定scheduler调度的strategy的过滤项，其变量定义如下（cli/flags.go）：

flStrategy = cli.StringFlag{
    Name:  "strategy",
    Usage: "placement strategy to use [" + strings.Join(strategy.List(), ", ") + "]",
    Value: strategy.List()[0],
}

strategy的默认值是SpreadPlacementStrategy。

strategy在代码中的实际定义是PlacementStrategy，一个interface：

// PlacementStrategy is the interface for a container placement strategy.
type PlacementStrategy interface {
    // Name of the strategy
    Name() string
    // Initialize performs any initial configuration required by the strategy and returns
    // an error if one is encountered.
    // If no initial configuration is needed, this may be a no-op and return a nil error.
    Initialize() error
    // RankAndSort applies the strategy to a list of nodes and ranks them based
    // on the best fit given the container configuration.  It returns a sorted
    // list of nodes (based on their ranks) or an error if there is no
    // available node on which to schedule the container.
    RankAndSort(config *cluster.ContainerConfig, nodes []*node.Node) ([]*node.Node, error)
}

其中RankAndSort返回一个符合条件node（也就是Docker Engine）列表，列表中元素按匹配度排序。

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