healthchecks.go

package main

import (
	"crypto/tls"
	"fmt"
	"net/http"
	"strconv"
	"time"

	"github.com/heptiolabs/healthcheck"
)

// HealthCheck registers and endpoint for healthchecking the service
type HealthCheck struct {
	port      int
	s3URL     string
	brokerURL string
	tlsConfig *tls.Config
}

// NewHealthCheck creates a new healthchecker. It needs to know where to find
// the backend S3 storage and the Message Broker so it can report readiness.
func NewHealthCheck(port int, s3 S3Config, broker BrokerConfig, tlsConfig *tls.Config) *HealthCheck {
	s3URL := s3.url
	if s3.readypath != "" {
		s3URL = s3.url + s3.readypath
	}

	brokerURL := broker.host + ":" + broker.port

	return &HealthCheck{port, s3URL, brokerURL, tlsConfig}
}

// RunHealthChecks should be run as a go routine in the main app. It registers
// the healthcheck handler on the port specified in when creating a new
// healthcheck.
func (h *HealthCheck) RunHealthChecks() {
	health := healthcheck.NewHandler()

	health.AddLivenessCheck("goroutine-threshold", healthcheck.GoroutineCountCheck(100))

	health.AddReadinessCheck("S3-backend-http", h.httpsGetCheck(h.s3URL, 5000*time.Millisecond))

	health.AddReadinessCheck("broker-tcp", healthcheck.TCPDialCheck(h.brokerURL, 50*time.Millisecond))

	addr := ":" + strconv.Itoa(h.port)
	server := &http.Server{
		Addr:              addr,
		Handler:           health,
		ReadTimeout:       5 * time.Second,
		WriteTimeout:      5 * time.Second,
		IdleTimeout:       30 * time.Second,
		ReadHeaderTimeout: 3 * time.Second,
	}
	if err := server.ListenAndServe(); err != nil {
		panic(err)
	}
}

func (h *HealthCheck) httpsGetCheck(url string, timeout time.Duration) healthcheck.Check {
	cfg := &tls.Config{MinVersion: tls.VersionTLS12}
	cfg.RootCAs = h.tlsConfig.RootCAs
	tr := &http.Transport{TLSClientConfig: cfg}
	client := http.Client{
		Transport: tr,
		Timeout:   timeout,
		// never follow redirects
		CheckRedirect: func(*http.Request, []*http.Request) error {
			return http.ErrUseLastResponse
		},
	}

	return func() error {
		resp, e := client.Get(url)
		if e != nil {
			return e
		}
		_ = resp.Body.Close() // ignoring error
		if resp.StatusCode != 200 {
			return fmt.Errorf("returned status %d", resp.StatusCode)
		}

		return nil
	}
}