Openfaas

1. ReadConfig (读取环境配置信息)
2. BasicAuthCredentials (基本的身份认证)

3. MakeForwardingProxyHandler (和函数相关的代理转发，net/http上抽象了一层) 
   - List: faasHandlers.ListFunctions
   - Deploy: faasHandlers.DeployFunction
   - Delete: faasHandlers.DeleteFunction
   - Update: faasHandlers.UpdateFunction 
   - Query: faasHandlers.QueryFunction
   - Info：faasHandlers.InfoHandler
   - Secret：faasHandlers.SecretHandler
   - Namespace: faasHandlers.NamespaceListerHandler
4. if ScaleFromZero : NewFunctionCache （参考 [zero-scale](https://www.openfaas.com/blog/zero-scale/)） 

5. If UseNATS : CreateNATSQueue (异步函数启用NATS，消息发布者角色)

6. NewPrometheusQuery（设置Prometheus监控）

7. Scale：faasHandlers.ScaleFunction（设置自动扩缩容）

8. mux.NewRouter()（注册各种路由）
9. go runMetricsServer()（启动Prometheus指标收集）
10. &http.Server{} => ListenAndServe （启动服务）

1) r = mux.NewRouter() （注册各种路由）

2) Serve
  2.1) if EnableBasicAuth: handlers.FunctionReader = auth.DecorateWithBasicAuth (鉴权) 

  2.2) r.HandleFunc("/system/***")  (处理 HTTP 请求等路由)
     r.HandleFunc("/function/***")
     r.HandleFunc("/healthz/***")

3) ListenAndServe()

type FaaSHandlers struct {
    // FunctionProxy provides the function invocation proxy logic.  Use proxy.NewHandlerFunc to
    // use the standard OpenFaaS proxy implementation or provide completely custom proxy logic.
    FunctionProxy http.HandlerFunc

    FunctionReader http.HandlerFunc
    DeployHandler  http.HandlerFunc

    DeleteHandler  http.HandlerFunc
    ReplicaReader  http.HandlerFunc
    ReplicaUpdater http.HandlerFunc
    SecretHandler  http.HandlerFunc
    // LogHandler provides streaming json logs of functions
    LogHandler http.HandlerFunc

    // UpdateHandler an existing function/service
    UpdateHandler http.HandlerFunc
    // HealthHandler defines the default health endpoint bound to "/healthz
    // If the handler is not set, then the "/healthz" path will not be configured
    HealthHandler        http.HandlerFunc
    InfoHandler          http.HandlerFunc
    ListNamespaceHandler http.HandlerFunc
}

// proxyRequest 处理调用函数服务的实际请求
func proxyRequest(...) {
    ...
    proxyReq = buildProxyRequest(originalReq, functionAddr, pathVars["params"])
}

// 拼装 Watchdog 的 Url，并代理过去
func buildProxyRequest(...) {
    f baseURL.Port() == "" {
        host = baseURL.Host + ":" + watchdogPort
    }

    url := url.URL{
        Scheme:   baseURL.Scheme,
        Host:     host,
        Path:     extraPath,
        RawQuery: originalReq.URL.RawQuery,
    }

    upstreamReq, err := http.NewRequest(originalReq.Method, url.String(), nil)
    if err != nil {
        return nil, err
    }
  ...
    return upstreamReq
}

main() {
    if !operator {
        runController(kubeconfig, masterURL) // 运行 k8s 的核心控制器
    } else {
        runOperator(kubeconfig, masterURL) // 操作 k8s 的CRD 资源，新增能力
    }
}
// masterURL： address of the Kubernetes API server
// operator：Use the operator mode instead of faas-netes

func runController(kubeconfig, masterURL string) {
    // 1. k8s namespace
    functionNamespace := "default"

    // 2. 获取 k8s, 探针，镜像拉取策略等配置信息
    deployConfig := k8s.DeploymentConfig{}

    // 3. k8s 客户端
    factory := k8s.NewFunctionFactory(clientset, deployConfig)

    // 4. 核心： k8s 操作句柄
    bootstrapHandlers := providertypes.FaaSHandlers{
            FunctionProxy:        proxy.NewHandlerFunc(cfg.FaaSConfig, functionLookup),
      DeleteHandler:        handlers.MakeDeleteHandler(functionNamespace, clientset),
      DeployHandler:        handlers.MakeDeployHandler(functionNamespace, factory),
      FunctionReader:       handlers.MakeFunctionReader(functionNamespace, clientset),
      ReplicaReader:        handlers.MakeReplicaReader(functionNamespace, clientset),
      ReplicaUpdater:       handlers.MakeReplicaUpdater(functionNamespace, clientset),
      UpdateHandler:        handlers.MakeUpdateHandler(functionNamespace, factory),
      HealthHandler:        handlers.MakeHealthHandler(),
      InfoHandler:          handlers.MakeInfoHandler(version.BuildVersion(), version.GitCommit),
      SecretHandler:        handlers.MakeSecretHandler(functionNamespace, clientset),
      LogHandler:           logs.NewLogHandlerFunc(k8s.NewLogRequestor(clientset, functionNamespace), cfg.FaaSConfig.WriteTimeout),
      ListNamespaceHandler: handlers.MakeNamespacesLister(functionNamespace, clientset),
    }

    // 5. 运行服务器
    faasProvider.Serve(&bootstrapHandlers, &cfg.FaaSConfig)
}

// 返回 delete handler
func MakeDeleteHandler() {
    return func{
            // ...
    deployment, findDeployErr := clientset.AppsV1().
      Deployments(lookupNamespace).
      Get(request.FunctionName, getOpts)
    if isFunction(deployment) {
        err := deleteFunction(lookupNamespace, clientset, request, w)
    }
    // ...  
    }
}

// 执行删除
func deleteFunction(..., clientset *kubernetes.Clientset, ...) {
    // 删除 deploy
    clientset.AppsV1().Deployments(functionNamespace).
        Delete(request.FunctionName, opts)

    // 删除 service
    clientset.CoreV1().
        Services(functionNamespace).
        Delete(request.FunctionName, opts); 
}

// 调用 Kubernetes API 进行的扩缩容，代码都差不多，不再赘述

func main() {
    // 1. 读取配置
    readConfig := ReadConfig{}
    config := readConfig.Read(osEnv)

    // 2. 处理请求
    http.HandleFunc("/_/health", makeHealthHandler())
    // 核心 makeRequestHandler
    http.HandleFunc("/", metrics.InstrumentHandler(makeRequestHandler(&config), httpMetrics))

    // 3. Promethus 服务
    go metricsServer.Serve(cancel)

    // 4. 函数服务
    listenUntilShutdown(shutdownTimeout, s, config.suppressLock)
}

// listen for HTTP 直到听到信号 SIGTERM 且等待超时后
func listenUntilShutdown() {
    // Run the HTTP server in a separate go-routine.
    go func() {
        if err := s.ListenAndServe(); err != http.ErrServerClosed {
            log.Printf("Error ListenAndServe: %v", err)
            close(idleConnsClosed)
        }
    }()
}

// 处理 Http 请求
func makeRequestHandler(config *WatchdogConfig) http.HandlerFunc {
    switch r.Method {
        case
            http.MethodPost,
            http.MethodPut,
            http.MethodPatch,
            http.MethodDelete,
            http.MethodGet:
            pipeRequest(config, w, r, r.Method)
            break
    }
}

// 核心：pipeRequest 
// 为每个请求 Fork 一个 fprocess
func pipeRequest() {
    // ...
    parts := strings.Split(config.faasProcess, " ") // faasProcess: "node index.js"
    // ...
    targetCmd := exec.Command(parts[0], parts[1:]...) // 执行函数
    // ...
    requestBody, buildInputErr = buildFunctionInput(config, r)
    // ...
}

// 格式化输入
buildFunctionInput(config *WatchdogConfig, r *http.Request) {
    //...
    return res, err
}

func (ReadConfig) Read(hasEnv HasEnv) WatchdogConfig {
    // ... 
    cfg.faasProcess = hasEnv.Getenv("fprocess")
    // ... 
}