setup.go

/*This file is part of kuberpult.

Kuberpult is free software: you can redistribute it and/or modify
it under the terms of the Expat(MIT) License as published by
the Free Software Foundation.

Kuberpult is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
MIT License for more details.

You should have received a copy of the MIT License
along with kuberpult. If not, see <https://directory.fsf.org/wiki/License:Expat>.

Copyright 2023 freiheit.com*/

// Setup implementation shared between all microservices.
// If this file is changed it will affect _all_ microservices in the monorepo (and this
// is deliberately so).
package setup

import (
	"context"
	"crypto/subtle"
	"fmt"
	"net"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"

	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/metric"
	"go.uber.org/zap"

	"github.com/freiheit-com/kuberpult/pkg/logger"
	"github.com/freiheit-com/kuberpult/pkg/metrics"
	"google.golang.org/grpc"
)

var (
	osSignalChannel = make(chan os.Signal, 1) // System writes here when shutdown
)

func init() {
	signal.Notify(osSignalChannel, syscall.SIGINT, syscall.SIGTERM)
}

type shutdown struct {
	name string
	fn   func(context.Context) error
}

// Setup structure that holds only the shutdown callbacks for all
// grpc and http server for endpoints, metrics, health checks, etc.
type setup struct {
	health          HealthServer
	shutdown        []shutdown
	shutdownChannel chan bool
}

type BasicAuth struct {
	Username string
	Password string
}

type GRPCConfig struct {
	// required
	Port     string
	Register func(*grpc.Server)
	Opts     []grpc.ServerOption

	// optional
	Shutdown func(context.Context) error
}

type HTTPConfig struct {
	// required
	Port     string
	Register func(*http.ServeMux)

	// optional
	BasicAuth *BasicAuth
	Shutdown  func(context.Context) error
}

type BackgroundFunc func(context.Context, *HealthReporter) error

type BackgroundTaskConfig struct {
	// a function that triggers a graceful shutdown of all other resources after completion
	Run  BackgroundFunc
	Name string
	// optional
	Shutdown func(context.Context) error
}

// Config contains configurations for all servers & tasks will be started.
// A startup order is not guaranteed.
type ServerConfig struct {
	GRPC *GRPCConfig
	HTTP []HTTPConfig
	// BackgroundTasks are tasks that are running forever, like Pub/sub receiver. If they
	// finish, a graceful shutdown will be triggered.
	Background []BackgroundTaskConfig
	Shutdown   func(context.Context) error
}

func Run(ctx context.Context, config ServerConfig) {
	s := &setup{}

	ctx, cancel := context.WithCancel(ctx)
	pv, handler, _ := metrics.Init()
	ctx = metrics.WithProvider(ctx, pv)

	pv.Meter("setup").Int64ObservableGauge("background_job_ready", metric.WithInt64Callback(func(_ context.Context, o metric.Int64Observer) error {
		reports := s.health.reports()
		for name, report := range reports {
			var value int64
			if report.isReady(s.health.now()) {
				value = 1
			}
			o.Observe(value, metric.WithAttributes(attribute.String("name", name)))
		}
		return nil
	}))

	// Start the listening on each protocol
	for _, cfg := range config.HTTP {
		setupHTTP(ctx, s, cfg, cancel, handler)
	}
	if config.GRPC != nil {
		setupGRPC(ctx, s, *config.GRPC, cancel)
	}
	for _, task := range config.Background {
		setupBackgroundTask(ctx, s, task, cancel)
	}

	if config.Shutdown != nil {
		s.RegisterShutdown(
			"global shutdown handler",
			config.Shutdown,
		)
	}

	// Listening for shutdown signal
	s.listenToShutdownSignal(ctx, cancel)
}

func (s *setup) RegisterShutdown(name string, shutdownFN func(ctx context.Context) error) {
	s.shutdown = append(s.shutdown, shutdown{name: name, fn: shutdownFN})
}

func (s *setup) listenToShutdownSignal(ctx context.Context, cancelFunc context.CancelFunc) {
	// Wait for a signal to shutdown all servers.
	// This should be a blocking call, because program will exit as soon as
	// the main goroutine returns (so it doesn't wait for other goroutines).
	// Non-blocking call could lead to unfinished cleanup during the shutdown.
	// See also https://golang.org/ref/spec#Program_execution
	select {
	case <-osSignalChannel:
	case <-ctx.Done():
	}

	// cancel the context
	cancelFunc()

	// call shutdown hooks
	gracefulShutdown(ctx, s, 30*time.Second)
}

func gracefulShutdown(ctx context.Context, s *setup, timeout time.Duration) {
	// Instantiate background context
	ctx, cancel := context.WithTimeout(context.Background(), timeout)
	defer cancel()

	for i := len(s.shutdown) - 1; i >= 0; i-- {
		sd := s.shutdown[i]
		if err := sd.fn(ctx); err != nil {
			logger.FromContext(ctx).Error("shutdown.failed", zap.Error(err), zap.String("handler", sd.name))
		}
	}
}

func setupGRPC(ctx context.Context, s *setup, config GRPCConfig, cancel context.CancelFunc) {
	// Get service listening port
	addrGRPC := ":" + config.Port

	// Setup a listener for gRPC port
	grpcL, err := net.Listen("tcp", addrGRPC)
	if err != nil {
		logger.FromContext(ctx).Panic("grpc.listen.error", zap.Error(err), zap.String("addr", addrGRPC))
		return
	}
	s.RegisterShutdown("GRPC net listener", func(context.Context) error {
		return grpcL.Close()
	})

	// Instantiate gRPC server
	grpcS := grpc.NewServer(config.Opts...)
	s.RegisterShutdown("GRPC server", func(context.Context) error {
		grpcS.GracefulStop()
		return nil
	})

	config.Register(grpcS)
	if config.Shutdown != nil {
		s.RegisterShutdown("GRPC shutdown handler", config.Shutdown)
	}

	go serveGRPC(ctx, grpcS, grpcL, cancel)
}

func serveGRPC(ctx context.Context, grpcS *grpc.Server, grpcL net.Listener, cancel context.CancelFunc) {
	defer cancel()

	if err := grpcS.Serve(grpcL); err != nil {
		logger.FromContext(ctx).Error("grpc.serve.error", zap.Error(err))
	}
}

func setupHTTP(ctx context.Context, s *setup, config HTTPConfig, cancel context.CancelFunc, metricHandler http.Handler) {
	mux := http.NewServeMux()
	if config.Register != nil {
		config.Register(mux)
	}
	mux.Handle("/metrics", metricHandler)
	mux.Handle("/healthz", &s.health)
	runHTTPHandler(ctx, s, mux, config.Port, config.BasicAuth, config.Shutdown, cancel)
}

func runHTTPHandler(ctx context.Context, s *setup, handler http.Handler, port string, basicAuth *BasicAuth, shutdown func(context.Context) error, cancel context.CancelFunc) {

	if basicAuth != nil {
		handler = NewBasicAuthHandler(basicAuth, handler)
	}

	httpS := &http.Server{
		Handler: handler,
	}
	s.RegisterShutdown(
		fmt.Sprintf("http server on %s", port),
		func(ctx context.Context) error {
			return shutdownHTTP(ctx, httpS)
		},
	)

	if shutdown != nil {
		s.RegisterShutdown(
			fmt.Sprintf("http shutdown handler on %s", port),
			shutdown,
		)
	}

	go serveHTTP(ctx, httpS, port, cancel)
}

var shutdownHTTP = func(ctx context.Context, httpS *http.Server) error {
	return httpS.Shutdown(ctx)
}

var serveHTTP = func(ctx context.Context, httpS *http.Server, port string, cancel context.CancelFunc) {
	// if this function returns, the server was stopped, so stop also all the other services
	defer cancel()

	addr := ":" + port

	httpL, err := net.Listen("tcp", addr)
	if err != nil {
		logger.FromContext(ctx).Panic("http.listen.error", zap.Error(err), zap.String("addr", addr))
		return
	}

	if err := httpS.Serve(httpL); err != nil && err != http.ErrServerClosed {
		logger.FromContext(ctx).Error("http.serve.error", zap.Error(err))
	}
}

func setupBackgroundTask(ctx context.Context, s *setup, config BackgroundTaskConfig, cancel context.CancelFunc) {

	if config.Shutdown != nil {
		s.RegisterShutdown(
			fmt.Sprintf("shutdown handler for %s", config.Name),
			config.Shutdown,
		)
	}
	reporter := s.health.Reporter(config.Name)

	go runBackgroundTask(ctx, config, cancel, reporter)
}

func runBackgroundTask(ctx context.Context, config BackgroundTaskConfig, cancel context.CancelFunc, reporter *HealthReporter) {
	defer cancel()
	if err := config.Run(ctx, reporter); err != nil {
		logger.FromContext(ctx).Error("background.error", zap.Error(err), zap.String("job", config.Name))
	}
}

func NewBasicAuthHandler(basicAuth *BasicAuth, chainedHandler http.Handler) http.Handler {
	return &BasicAuthHandler{
		basicAuth:      basicAuth,
		chainedHandler: chainedHandler,
	}
}

type BasicAuthHandler struct {
	basicAuth      *BasicAuth
	chainedHandler http.Handler
}

func (h *BasicAuthHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
	reqUser, reqPass, ok := req.BasicAuth()
	if !ok || subtle.ConstantTimeCompare([]byte(reqUser), []byte(h.basicAuth.Username)) != 1 || subtle.ConstantTimeCompare([]byte(reqPass), []byte(h.basicAuth.Password)) != 1 {
		rw.Header().Set("WWW-Authenticate", `Basic realm="Please enter credentials"`)
		rw.WriteHeader(401)
		_, _ = rw.Write([]byte("Unauthorised.\n"))
		return
	}
	h.chainedHandler.ServeHTTP(rw, req)
}