Add healthcheck endpoint

health.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"net/http"
+	"time"
+	"fmt"
+
+	"github.com/pkg/errors"
+)
+
+const alertAfterMinutes = 5
+
+
+func (app app) healthHandler() func(http.ResponseWriter, *http.Request, loginParams) error {
+	return func(w http.ResponseWriter, r *http.Request, p loginParams) error {
+
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+
+		lastSampleTime, err := app.ndb.selectLastCrawlTime()
+		if err != nil {
+			// Return a 500 error
+			return errors.Wrap(err, "getting last crawl time")
+		}
+
+		if time.Now().Unix()-int64(lastSampleTime) > alertAfterMinutes*60 {
+			return fmt.Errorf("last successful crawl of %d is more than %d minutes ago", lastSampleTime, alertAfterMinutes)
+		}
+
+		// write "ok"
+		_, err = w.Write([]byte("ok"))
+		if err != nil {
+			return errors.Wrap(err, "writing response")
+		}
+
+		return nil
+	}
+}
+

httpserver.go

@@ -68,6 +68,8 @@ func (app app) httpServer(onPanic func(error)) *http.Server {
 	router.GET("/login", middleware("login", l, onPanic, app.loginHandler()))
 	router.GET("/logout", middleware("logout", l, onPanic, app.logoutHandler()))
 
+	router.GET("/health", middleware("health", l, onPanic, app.healthHandler()))
+
 	server.Handler = app.preRouterMiddleware(router, writeTimeout-100*time.Millisecond)
 
 	return server