Confd源码阅读

核心对象

TemplateResource is the representation of a parsed template resource.

type TemplateResource struct {
	CheckCmd      string `toml:"check_cmd"`
	Dest          string
	FileMode      os.FileMode
	Gid           int
	Keys          []string
	Mode          string
	Prefix        string
	ReloadCmd     string `toml:"reload_cmd"`
	Src           string
	StageFile     *os.File
	Uid           int
	funcMap       map[string]interface{}
	lastIndex     uint64
	keepStageFile bool
	noop          bool
	store         memkv.Store
	storeClient   backends.StoreClient
	syncOnly      bool
	PGPPrivateKey []byte
}

配置更新

process is a convenience function that wraps calls to the three main tasks required to keep local configuration files in sync. First we gather vars from the store, then we stage a candidate configuration file, and finally sync things up. It returns an error if any.

func (t *TemplateResource) process() error {
	if err := t.setFileMode(); err != nil {
		return err
	}
	if err := t.setVars(); err != nil {
		return err
	}
	if err := t.createStageFile(); err != nil {
		return err
	}
	if err := t.sync(); err != nil {
		return err
	}
	return nil
}

1. 从存储中获取变量
2. 暂存配置文件
3. 同步

定时刷新的实现

type intervalProcessor struct {
	config   Config
	stopChan chan bool
	doneChan chan bool
	errChan  chan error
	interval int
}

订阅刷新的实现

type watchProcessor struct {
	config   Config
	stopChan chan bool
	doneChan chan bool
	errChan  chan error
	wg       sync.WaitGroup
}

订阅的实现

store cline 提供两个方法

// The StoreClient interface is implemented by objects that can retrieve
// key/value pairs from a backend store.
type StoreClient interface {
	GetValues(keys []string) (map[string]string, error)
	WatchPrefix(prefix string, keys []string, waitIndex uint64, stopChan chan bool) (uint64, error)
}

主要看一下consul的实现

func (c *ConsulClient) WatchPrefix(prefix string, keys []string, waitIndex uint64, stopChan chan bool) (uint64, error) {
	respChan := make(chan watchResponse)
	go func() {
		opts := api.QueryOptions{
			WaitIndex: waitIndex,
		}
		_, meta, err := c.client.List(prefix, &opts)
		if err != nil {
			respChan <- watchResponse{waitIndex, err}
			return
		}
		respChan <- watchResponse{meta.LastIndex, err}
	}()

	select {
	case <-stopChan:
		return waitIndex, nil
	case r := <-respChan:
		return r.waitIndex, r.err
	}
}

总结

根据命名简要的看完了confd的配置更新的代码。confd支持两种模式的Processor，1. 定时更新（缺省）；2. 订阅更新。定时更新特别简单，周期从k/v存储中拉去变量，然后新建临时的配置文件，最后用新建的临时配置文件替换目标位置的配置。定时更新的主要区别是，通过创建channel去订阅（阻塞查询）k/v存储中关系的index有误发生变化。