confd的源码参考:https://github.com/kelseyhightower/confd

本文分析的confd的版本是v0.16.0,代码参考:https://github.com/kelseyhightower/confd/tree/v0.16.0。

1. Main

confd的入口函数 Main 函数,先解析参数,如果是打印版本信息的参数,则执行打印版本的命令。

func main() {
    flag.Parse()
    if config.PrintVersion {
        fmt.Printf("confd %s (Git SHA: %s, Go Version: %s)\n", Version, GitSHA, runtime.Version())
        os.Exit(0)
    }
    ...
}

其中版本信息记录在https://github.com/kelseyhightower/confd/blob/v0.16.0/version.go#L3

const Version = "0.16.0"

1.1. initConfig

初始化配置文件。

if err := initConfig(); err != nil {
    log.Fatal(err.Error())
}

initConfig函数对基本的配置内容做初始化,当没有指定后端存储的时候,设置默认存储。

// initConfig initializes the confd configuration by first setting defaults,
// then overriding settings from the confd config file, then overriding
// settings from environment variables, and finally overriding
// settings from flags set on the command line.
// It returns an error if any.
func initConfig() error {
    _, err := os.Stat(config.ConfigFile)
    if os.IsNotExist(err) {
        log.Debug("Skipping confd config file.")
    } else {
        log.Debug("Loading " + config.ConfigFile)
        configBytes, err := ioutil.ReadFile(config.ConfigFile)
        if err != nil {
            return err
        }

        _, err = toml.Decode(string(configBytes), &config)
        if err != nil {
            return err
        }
    }

    // Update config from environment variables.
    processEnv()

    if config.SecretKeyring != "" {
        kr, err := os.Open(config.SecretKeyring)
        if err != nil {
            log.Fatal(err.Error())
        }
        defer kr.Close()
        config.PGPPrivateKey, err = ioutil.ReadAll(kr)
        if err != nil {
            log.Fatal(err.Error())
        }
    }

    if config.LogLevel != "" {
        log.SetLevel(config.LogLevel)
    }

    if config.SRVDomain != "" && config.SRVRecord == "" {
        config.SRVRecord = fmt.Sprintf("_%s._tcp.%s.", config.Backend, config.SRVDomain)
    }

    // Update BackendNodes from SRV records.
    if config.Backend != "env" && config.SRVRecord != "" {
        log.Info("SRV record set to " + config.SRVRecord)
        srvNodes, err := getBackendNodesFromSRV(config.SRVRecord)
        if err != nil {
            return errors.New("Cannot get nodes from SRV records " + err.Error())
        }

        switch config.Backend {
        case "etcd":
            vsm := make([]string, len(srvNodes))
            for i, v := range srvNodes {
                vsm[i] = config.Scheme + "://" + v
            }
            srvNodes = vsm
        }

        config.BackendNodes = srvNodes
    }
    if len(config.BackendNodes) == 0 {
        switch config.Backend {
        case "consul":
            config.BackendNodes = []string{"127.0.0.1:8500"}
        case "etcd":
            peerstr := os.Getenv("ETCDCTL_PEERS")
            if len(peerstr) > 0 {
                config.BackendNodes = strings.Split(peerstr, ",")
            } else {
                config.BackendNodes = []string{"http://127.0.0.1:4001"}
            }
        case "etcdv3":
            config.BackendNodes = []string{"127.0.0.1:2379"}
        case "redis":
            config.BackendNodes = []string{"127.0.0.1:6379"}
        case "vault":
            config.BackendNodes = []string{"http://127.0.0.1:8200"}
        case "zookeeper":
            config.BackendNodes = []string{"127.0.0.1:2181"}
        }
    }
    // Initialize the storage client
    log.Info("Backend set to " + config.Backend)

    if config.Watch {
        unsupportedBackends := map[string]bool{
            "dynamodb": true,
            "ssm":      true,
        }

        if unsupportedBackends[config.Backend] {
            log.Info(fmt.Sprintf("Watch is not supported for backend %s. Exiting...", config.Backend))
            os.Exit(1)
        }
    }

    if config.Backend == "dynamodb" && config.Table == "" {
        return errors.New("No DynamoDB table configured")
    }
    config.ConfigDir = filepath.Join(config.ConfDir, "conf.d")
    config.TemplateDir = filepath.Join(config.ConfDir, "templates")
    return nil
}

1.2. storeClient

log.Info("Starting confd")

storeClient, err := backends.New(config.BackendsConfig)
if err != nil {
    log.Fatal(err.Error())
}

根据配置文件中的存储后端类型构造一个存储后端的client,其中主要调用的函数为backends.New(config.BackendsConfig)

当没有设置存储后端时,默认为etcd

if config.Backend == "" {
    config.Backend = "etcd"
}
backendNodes := config.BackendNodes

当存储后端为file类型的处理。

if config.Backend == "file" {
    log.Info("Backend source(s) set to " + strings.Join(config.YAMLFile, ", "))
} else {
    log.Info("Backend source(s) set to " + strings.Join(backendNodes, ", "))
}

最后再根据不同类型的存储后端,调用不同的存储后端构建函数,本文只分析redis类型的存储后端。

switch config.Backend {
case "consul":
    return consul.New(config.BackendNodes, config.Scheme,
        config.ClientCert, config.ClientKey,
        config.ClientCaKeys,
        config.BasicAuth,
        config.Username,
        config.Password,
    )
case "etcd":
    // Create the etcd client upfront and use it for the life of the process.
    // The etcdClient is an http.Client and designed to be reused.
    return etcd.NewEtcdClient(backendNodes, config.ClientCert, config.ClientKey, config.ClientCaKeys, config.BasicAuth, config.Username, config.Password)
case "etcdv3":
    return etcdv3.NewEtcdClient(backendNodes, config.ClientCert, config.ClientKey, config.ClientCaKeys, config.BasicAuth, config.Username, config.Password)
case "zookeeper":
    return zookeeper.NewZookeeperClient(backendNodes)
case "rancher":
    return rancher.NewRancherClient(backendNodes)
case "redis":
    return redis.NewRedisClient(backendNodes, config.ClientKey, config.Separator)
case "env":
    return env.NewEnvClient()
case "file":
    return file.NewFileClient(config.YAMLFile, config.Filter)
case "vault":
    vaultConfig := map[string]string{
        "app-id":    config.AppID,
        "user-id":   config.UserID,
        "role-id":   config.RoleID,
        "secret-id": config.SecretID,
        "username":  config.Username,
        "password":  config.Password,
        "token":     config.AuthToken,
        "cert":      config.ClientCert,
        "key":       config.ClientKey,
        "caCert":    config.ClientCaKeys,
        "path":      config.Path,
    }
    return vault.New(backendNodes[0], config.AuthType, vaultConfig)
case "dynamodb":
    table := config.Table
    log.Info("DynamoDB table set to " + table)
    return dynamodb.NewDynamoDBClient(table)
case "ssm":
    return ssm.New()
}
return nil, errors.New("Invalid backend")

其中redis类型的存储后端调用了NewRedisClient方法来构造redis的client。

case "redis":
    return redis.NewRedisClient(backendNodes, config.ClientKey, config.Separator)

其中涉及三个参数:

  • backendNodes:redis的节点地址。
  • ClientKey:redis的密码。
  • Separator:查找redis键的分隔符,该参数只用在redis类型。

NewRedisClient函数方法如下:

// NewRedisClient returns an *redis.Client with a connection to named machines.
// It returns an error if a connection to the cluster cannot be made.
func NewRedisClient(machines []string, password string, separator string) (*Client, error) {
    if separator == "" {
        separator = "/"
    }
    log.Debug(fmt.Sprintf("Redis Separator: %#v", separator))
    var err error
    clientWrapper := &Client{machines: machines, password: password, separator: separator, client: nil, pscChan: make(chan watchResponse), psc: redis.PubSubConn{Conn: nil} }
    clientWrapper.client, _, err = tryConnect(machines, password, true)
    return clientWrapper, err
}

1.3. processor

stopChan := make(chan bool)
doneChan := make(chan bool)
errChan := make(chan error, 10)

var processor template.Processor
switch {
case config.Watch:
    processor = template.WatchProcessor(config.TemplateConfig, stopChan, doneChan, errChan)
default:
    processor = template.IntervalProcessor(config.TemplateConfig, stopChan, doneChan, errChan, config.Interval)
}

go processor.Process()

当开启watch参数的时候,则构造WatchProcessor,否则构造IntervalProcessor,最后起一个goroutine。

go processor.Process()

这块的逻辑在本文第二部分析。

1.4. signalChan

signalChan := make(chan os.Signal, 1)
signal.Notify(signalChan, syscall.SIGINT, syscall.SIGTERM)
for {
    select {
    case err := <-errChan:
        log.Error(err.Error())
    case s := <-signalChan:
        log.Info(fmt.Sprintf("Captured %v. Exiting...", s))
        close(doneChan)
    case <-doneChan:
        os.Exit(0)
    }
}

2. Process

type Processor interface {
    Process()
}

Processor是一个接口类型,主要的实现体有:

  • intervalProcessor:默认的实现体,即没有添加watch参数。
  • watchProcessor:添加watch参数的实现体。

2.1. intervalProcessor

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

intervalProcessor根据config内容和几个channel构造一个intervalProcessor。

func IntervalProcessor(config Config, stopChan, doneChan chan bool, errChan chan error, interval int) Processor {
    return &intervalProcessor{config, stopChan, doneChan, errChan, interval}
}

2.1.1. intervalProcessor.Process

func (p *intervalProcessor) Process() {
    defer close(p.doneChan)
    for {
        ts, err := getTemplateResources(p.config)
        if err != nil {
            log.Fatal(err.Error())
            break
        }
        process(ts)
        select {
        case <-p.stopChan:
            break
        case <-time.After(time.Duration(p.interval) * time.Second):
            continue
        }
    }
}

通过解析config内容获取TemplateResources,其中核心函数为process(ts),然后执行t.process(),该函数中会调用t.sync()t.process()的具体逻辑后文分析。

func process(ts []*TemplateResource) error {
    var lastErr error
    for _, t := range ts {
        if err := t.process(); err != nil {
            log.Error(err.Error())
            lastErr = err
        }
    }
    return lastErr
}

2.2. watchProcessor

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

watchProcessor根据config内容和几个channel构造一个watchProcessor。

func WatchProcessor(config Config, stopChan, doneChan chan bool, errChan chan error) Processor {
    var wg sync.WaitGroup
    return &watchProcessor{config, stopChan, doneChan, errChan, wg}
}

2.2.1. watchProcessor.Process

func (p *watchProcessor) Process() {
    defer close(p.doneChan)
    ts, err := getTemplateResources(p.config)
    if err != nil {
        log.Fatal(err.Error())
        return
    }
    for _, t := range ts {
        t := t
        p.wg.Add(1)
        go p.monitorPrefix(t)
    }
    p.wg.Wait()
}

watchProcessor.Process方法实现了Processor接口中定义的方法,通过解析config内容获取TemplateResources,再遍历TemplateResources执行monitorPrefix,有多少个TemplateResources就运行多少个monitorPrefix的goroutine。

2.2.2. monitorPrefix

func (p *watchProcessor) monitorPrefix(t *TemplateResource) {
    defer p.wg.Done()
    keys := util.AppendPrefix(t.Prefix, t.Keys)
    for {
        index, err := t.storeClient.WatchPrefix(t.Prefix, keys, t.lastIndex, p.stopChan)
        if err != nil {
            p.errChan <- err
            // Prevent backend errors from consuming all resources.
            time.Sleep(time.Second * 2)
            continue
        }
        t.lastIndex = index
        if err := t.process(); err != nil {
            p.errChan <- err
        }
    }
}

先对配置文件中的prefixkeys参数进行拼接。

keys := util.AppendPrefix(t.Prefix, t.Keys)

AppendPrefix函数如下:

func AppendPrefix(prefix string, keys []string) []string {
    s := make([]string, len(keys))
    for i, k := range keys {
        s[i] = path.Join(prefix, k)
    }
    return s
}

接着再执行storeClientWatchPrefix方法,因为storeClient是一个接口,对应不同类型的存储后端,WatchPrefix的实现逻辑也不同,本文分析的存储类型为redis

index, err := t.storeClient.WatchPrefix(t.Prefix, keys, t.lastIndex, p.stopChan)
if err != nil {
    p.errChan <- err
    // Prevent backend errors from consuming all resources.
    time.Sleep(time.Second * 2)
    continue
}

storeClient.WatchPrefix主要是获取lastIndex的值,这个值在t.process()中使用。

t.lastIndex = index
if err := t.process(); err != nil {
    p.errChan <- err
}

2.3. TemplateResource.process

无论是否加watch参数,即intervalProcessorwatchProcessor最终都会调用到TemplateResource.process这个函数,而这个函数中的核心函数为t.sync()

// 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
}

2.3.1. setFileMode

setFileMode设置文件的权限,如果没有在配置文件指定mode参数则默认为0644,否则根据配置文件中指定的mode来设置文件权限。

// setFileMode sets the FileMode.
func (t *TemplateResource) setFileMode() error {
    if t.Mode == "" {
        if !util.IsFileExist(t.Dest) {
            t.FileMode = 0644
        } else {
            fi, err := os.Stat(t.Dest)
            if err != nil {
                return err
            }
            t.FileMode = fi.Mode()
        }
    } else {
        mode, err := strconv.ParseUint(t.Mode, 0, 32)
        if err != nil {
            return err
        }
        t.FileMode = os.FileMode(mode)
    }
    return nil
}

2.3.2. setVars

setVars将后端存储中最新的值拿出来暂存到内存中供后续进程使用。其中根据不同的后端,storeClient.GetValues的逻辑可能不同,但通过接口的方式可以让不同的存储后端实现不同的获取值的方法。

// setVars sets the Vars for template resource.
func (t *TemplateResource) setVars() error {
    var err error
    log.Debug("Retrieving keys from store")
    log.Debug("Key prefix set to " + t.Prefix)

    result, err := t.storeClient.GetValues(util.AppendPrefix(t.Prefix, t.Keys))
    if err != nil {
        return err
    }
    log.Debug("Got the following map from store: %v", result)

    t.store.Purge()

    for k, v := range result {
        t.store.Set(path.Join("/", strings.TrimPrefix(k, t.Prefix)), v)
    }
    return nil
}

2.3.3. createStageFile

createStageFile通过srctemplate文件和最新内存中的变量数据生成StageFile,该文件在sync中和目标文件进行比较,看是否有修改。即StageFile实际上是根据后端存储生成的最新的配置文件,如果这份配置文件跟当前的配置文件不同,表明后端存储的数据被更新了需要重新生成一份新的配置文件。

// createStageFile stages the src configuration file by processing the src
// template and setting the desired owner, group, and mode. It also sets the
// StageFile for the template resource.
// It returns an error if any.
func (t *TemplateResource) createStageFile() error {
    log.Debug("Using source template " + t.Src)

    if !util.IsFileExist(t.Src) {
        return errors.New("Missing template: " + t.Src)
    }

    log.Debug("Compiling source template " + t.Src)

    tmpl, err := template.New(filepath.Base(t.Src)).Funcs(t.funcMap).ParseFiles(t.Src)
    if err != nil {
        return fmt.Errorf("Unable to process template %s, %s", t.Src, err)
    }

    // create TempFile in Dest directory to avoid cross-filesystem issues
    temp, err := ioutil.TempFile(filepath.Dir(t.Dest), "."+filepath.Base(t.Dest))
    if err != nil {
        return err
    }

    if err = tmpl.Execute(temp, nil); err != nil {
        temp.Close()
        os.Remove(temp.Name())
        return err
    }
    defer temp.Close()

    // Set the owner, group, and mode on the stage file now to make it easier to
    // compare against the destination configuration file later.
    os.Chmod(temp.Name(), t.FileMode)
    os.Chown(temp.Name(), t.Uid, t.Gid)
    t.StageFile = temp
    return nil
}

2.3.4. sync

if err := t.sync(); err != nil {
    return err
}

t.sync()是执行confd核心功能的函数,将配置文件通过模板的方式自动生成,并执行检查命令和reload命令。该部分逻辑在本文第三部分分析。

3. sync

sync通过比较源文件和目标文件的差别,如果不同则重新生成新的配置,当设置了check_cmdreload_cmd的时候,会执行check_cmd指定的检查命令,如果都没有问题则执行reload_cmd中指定的reload命令。

3.1. IsConfigChanged

IsConfigChanged比较源文件和目标文件是否相等,其中比较内容包括:UidGidModeMd5。只要其中任意值不同则认为两个文件不同。

// IsConfigChanged reports whether src and dest config files are equal.
// Two config files are equal when they have the same file contents and
// Unix permissions. The owner, group, and mode must match.
// It return false in other cases.
func IsConfigChanged(src, dest string) (bool, error) {
    if !IsFileExist(dest) {
        return true, nil
    }
    d, err := FileStat(dest)
    if err != nil {
        return true, err
    }
    s, err := FileStat(src)
    if err != nil {
        return true, err
    }
    if d.Uid != s.Uid {
        log.Info(fmt.Sprintf("%s has UID %d should be %d", dest, d.Uid, s.Uid))
    }
    if d.Gid != s.Gid {
        log.Info(fmt.Sprintf("%s has GID %d should be %d", dest, d.Gid, s.Gid))
    }
    if d.Mode != s.Mode {
        log.Info(fmt.Sprintf("%s has mode %s should be %s", dest, os.FileMode(d.Mode), os.FileMode(s.Mode)))
    }
    if d.Md5 != s.Md5 {
        log.Info(fmt.Sprintf("%s has md5sum %s should be %s", dest, d.Md5, s.Md5))
    }
    if d.Uid != s.Uid || d.Gid != s.Gid || d.Mode != s.Mode || d.Md5 != s.Md5 {
        return true, nil
    }
    return false, nil
}

如果文件发生改变则执行check_cmd命令(有配置的情况下),重新生成配置文件,并执行reload_cmd命令(有配置的情况下)。

if ok {
    log.Info("Target config " + t.Dest + " out of sync")
    if !t.syncOnly && t.CheckCmd != "" {
        if err := t.check(); err != nil {
            return errors.New("Config check failed: " + err.Error())
        }
    }
    log.Debug("Overwriting target config " + t.Dest)
    err := os.Rename(staged, t.Dest)
    if err != nil {
        if strings.Contains(err.Error(), "device or resource busy") {
            log.Debug("Rename failed - target is likely a mount. Trying to write instead")
            // try to open the file and write to it
            var contents []byte
            var rerr error
            contents, rerr = ioutil.ReadFile(staged)
            if rerr != nil {
                return rerr
            }
            err := ioutil.WriteFile(t.Dest, contents, t.FileMode)
            // make sure owner and group match the temp file, in case the file was created with WriteFile
            os.Chown(t.Dest, t.Uid, t.Gid)
            if err != nil {
                return err
            }
        } else {
            return err
        }
    }
    if !t.syncOnly && t.ReloadCmd != "" {
        if err := t.reload(); err != nil {
            return err
        }
    }
    log.Info("Target config " + t.Dest + " has been updated")
} else {
    log.Debug("Target config " + t.Dest + " in sync")
}

3.2. check

check检查暂存的配置文件即stageFile,该文件是由最新的后端存储中的数据生成的。

if !t.syncOnly && t.CheckCmd != "" {
    if err := t.check(); err != nil {
        return errors.New("Config check failed: " + err.Error())
    }
}

t.check()只是执行配置文件中checkcmd参数指定的命令而已,根据是否执行成功来返回报错。当check命令产生错误的是,则直接return报错,不再执行重新生成配置文件和`reload的操作了。

// check executes the check command to validate the staged config file. The
// command is modified so that any references to src template are substituted
// with a string representing the full path of the staged file. This allows the
// check to be run on the staged file before overwriting the destination config
// file.
// It returns nil if the check command returns 0 and there are no other errors.
func (t *TemplateResource) check() error {
    var cmdBuffer bytes.Buffer
    data := make(map[string]string)
    data["src"] = t.StageFile.Name()
    tmpl, err := template.New("checkcmd").Parse(t.CheckCmd)
    if err != nil {
        return err
    }
    if err := tmpl.Execute(&cmdBuffer, data); err != nil {
        return err
    }
    return runCommand(cmdBuffer.String())
}

check会通过模板解析的方式解析出checkcmd中的{{.src}}部分,并用stageFile来替代。即check的命令是拉取最新后端存储的数据形成临时配置文件(stageFile),并通过指定的checkcmd来检查最新的临时配置文件是否合法,如果合法则替换会新的配置文件,否则返回错误。

3.3. Overwriting

staged文件命名为Dest文件的名字,读取staged文件中的内容并将它写入到Dest文件中,该过程实际上就是重新生成一份新的配置文件。staged文件的生成逻辑在函数createStageFile中。

log.Debug("Overwriting target config " + t.Dest)
err := os.Rename(staged, t.Dest)
if err != nil {
    if strings.Contains(err.Error(), "device or resource busy") {
        log.Debug("Rename failed - target is likely a mount. Trying to write instead")
        // try to open the file and write to it
        var contents []byte
        var rerr error
        contents, rerr = ioutil.ReadFile(staged)
        if rerr != nil {
            return rerr
        }
        err := ioutil.WriteFile(t.Dest, contents, t.FileMode)
        // make sure owner and group match the temp file, in case the file was created with WriteFile
        os.Chown(t.Dest, t.Uid, t.Gid)
        if err != nil {
            return err
        }
    } else {
        return err
    }
}

3.4. reload

如果没有指定syncOnly参数并且指定了ReloadCmd则执行reload操作。

if !t.syncOnly && t.ReloadCmd != "" {
    if err := t.reload(); err != nil {
        return err
    }
}

其中t.reload()实现如下:

// reload executes the reload command.
// It returns nil if the reload command returns 0.
func (t *TemplateResource) reload() error {
    return runCommand(t.ReloadCmd)
}

t.reload()t.check()都调用了runCommand函数:

// runCommand is a shared function used by check and reload
// to run the given command and log its output.
// It returns nil if the given cmd returns 0.
// The command can be run on unix and windows.
func runCommand(cmd string) error {
    log.Debug("Running " + cmd)
    var c *exec.Cmd
    if runtime.GOOS == "windows" {
        c = exec.Command("cmd", "/C", cmd)
    } else {
        c = exec.Command("/bin/sh", "-c", cmd)
    }

    output, err := c.CombinedOutput()
    if err != nil {
        log.Error(fmt.Sprintf("%q", string(output)))
        return err
    }
    log.Debug(fmt.Sprintf("%q", string(output)))
    return nil
}

4. redisClient.WatchPrefix

redisClient.WatchPrefix是当用户设置了watch参数的时候,并且存储后端为redis,则会调用到redis的watch机制。其中redisClient.WatchPrefix是redis存储类型的时候实现了StoreClient接口的WatchPrefix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)
}

StoreClient是对后端存储类型的抽象,常用的后端存储类型有EtcdRedis等,不同的后端存储类型GetValuesWatchPrefix的具体实现不同,本文主要分析Redis类型的watch机制。

4.1. WatchPrefix

WatchPrefix的调用函数在monitorPrefix的部分,具体参考:

func (p *watchProcessor) monitorPrefix(t *TemplateResource) {
    defer p.wg.Done()
    keys := util.AppendPrefix(t.Prefix, t.Keys)
    for {
        index, err := t.storeClient.WatchPrefix(t.Prefix, keys, t.lastIndex, p.stopChan)
        if err != nil {
            p.errChan <- err
            // Prevent backend errors from consuming all resources.
            time.Sleep(time.Second * 2)
            continue
        }
        t.lastIndex = index
        if err := t.process(); err != nil {
            p.errChan <- err
        }
    }
}

redis的watch主要通过pub-sub的机制,即WatchPrefix会根据传入的prefix起一个sub的监听机制,而在写入redis的数据的同时需要执行redis的publish操作,channel为符合prefix的值,value为给定命令之一,实际上是给定命令之一,具体是什么命令并没有关系,则会触发watch机制,从而自动更新配置,给定的命令列表如下:

"del", "append", "rename_from", "rename_to", "expire", "set", "incrby", "incrbyfloat", "hset", "hincrby", "hincrbyfloat", "hdel"

sub监听的key的格式如下:

__keyspace@0__:{prefix}/*

如果只是写入redis数据而没有自动执行publish的操作,并不会触发redis的watch机制来自动更新配置。但是如果使用etcd,则etcd的watch机制,只需要用户写入或更新数据就可以自动触发更新配置。

WatchPrefix源码如下:

func (c *Client) WatchPrefix(prefix string, keys []string, waitIndex uint64, stopChan chan bool) (uint64, error) {

    if waitIndex == 0 {
        return 1, nil
    }

    if len(c.pscChan) > 0 {
        var respChan watchResponse
        for len(c.pscChan) > 0 {
            respChan = <-c.pscChan
        }
        return respChan.waitIndex, respChan.err
    }

    go func() {
        if c.psc.Conn == nil {
            rClient, db, err := tryConnect(c.machines, c.password, false);

            if err != nil {
                c.psc = redis.PubSubConn{Conn: nil}
                c.pscChan <- watchResponse{0, err}
                return
            }

            c.psc = redis.PubSubConn{Conn: rClient}        

            go func() {
                defer func() {
                    c.psc.Close()
                    c.psc = redis.PubSubConn{Conn: nil}
                }()
                for {
                    switch n := c.psc.Receive().(type) {
                        case redis.PMessage:
                            log.Debug(fmt.Sprintf("Redis Message: %s %s\n", n.Channel, n.Data))
                            data := string(n.Data)
                            commands := [12]string{"del", "append", "rename_from", "rename_to", "expire", "set", "incrby", "incrbyfloat", "hset", "hincrby", "hincrbyfloat", "hdel"}
                            for _, command := range commands {
                                if command == data {
                                    c.pscChan <- watchResponse{1, nil}
                                    break
                                }
                            }
                        case redis.Subscription:
                            log.Debug(fmt.Sprintf("Redis Subscription: %s %s %d\n", n.Kind, n.Channel, n.Count))
                            if n.Count == 0 {
                                c.pscChan <- watchResponse{0, nil}
                                return
                            }
                        case error:
                            log.Debug(fmt.Sprintf("Redis error: %v\n", n))
                            c.pscChan <- watchResponse{0, n}
                            return
                    }
                }
            }()

            c.psc.PSubscribe("__keyspace@" + strconv.Itoa(db) + "__:" + c.transform(prefix) + "*")
        }
    }()

    select {
    case <-stopChan:
        c.psc.PUnsubscribe()
        return waitIndex, nil
    case r := <- c.pscChan:
        return r.waitIndex, r.err
    }
}

5. 总结

  1. confd的作用是通过将配置存放到存储后端,来自动触发更新配置的功能,其中常用的后端有EtcdRedis等。
  2. 不同的存储后端,watch机制不同,例如Etcd只需要更新key便可以触发自动更新配置的操作,而redis除了更新key还需要执行publish的操作。
  3. 可以通过配置check_cmd来校验配置文件是否正确,如果配置文件非法则不会执行自动更新配置和reload的操作,但是当存储后端存入的非法数据,会导致每次校验都是失败的,即使后面新增的配置部分是合法的,所以需要有机制来控制存入存储后端的数据始终是合法的。

参考:

Copyright © https://enpsl.github.io/ 2019-2020 all right reserved,powered by GitbookUpdated at 2018-12-10 20:38:30

results matching ""

    No results matching ""