golang healthcheck example

main.go

package main

import (
	"database/sql"
	"encoding/json"
	"fmt"
	"net/http"

	_ "github.com/go-sql-driver/mysql"
)

type HealthState struct {
	State         int
	ErrorMessages []string
}

func main() {

	http.HandleFunc("/healthcheck", handleRequest)

	http.ListenAndServe(":3001", nil)
}

func handleRequest(w http.ResponseWriter, r *http.Request) {

	outputState := &HealthState{}
	checkWeb(outputState)
	checkMysql(outputState)

	if len(outputState.ErrorMessages) > 0 {
		outputState.State = http.StatusServiceUnavailable
	} else {
		outputState.State = http.StatusOK
	}

	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(outputState.State)
	json.NewEncoder(w).Encode(outputState)
}

func checkWeb(outputState *HealthState) {
	resp, err := http.Get("https://medium.com")
	if err != nil || resp.StatusCode < 200 || resp.StatusCode > 299 {
		outputState.ErrorMessages = append(outputState.ErrorMessages, fmt.Sprintf("WebUI: %s", err.Error()))
	}
}

func checkMysql(outputState *HealthState) {
	db, err := sql.Open("mysql", "user:pass@tcp(127.0.0.1:3306)/dbname")
	if err != nil {
		outputState.ErrorMessages = append(outputState.ErrorMessages, fmt.Sprintf("MYSQL: %s", err.Error()))
	} else {
		defer db.Close()
	}
	err = db.Ping()
	if err != nil {
		outputState.ErrorMessages = append(outputState.ErrorMessages, fmt.Sprintf("MYSQL: %s", err.Error()))
	}
}