Healthcheck in docker container (#10)

Dockerfile

@@ -25,7 +25,8 @@ ARG opts
 RUN env ${opts} make build
 
 # final stage
-FROM scratch
+FROM alpine
+RUN apk add --no-cache bind-tools
 COPY --from=build-env /src/bin/blocky /app/blocky
 
 # the timezone data:
@@ -35,4 +36,6 @@ COPY --from=build-env /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
 
 WORKDIR /app
 
+HEALTHCHECK --interval=1m --timeout=3s CMD dig @127.0.0.1 -p 53 healthcheck.blocky +tcp || exit 1
+
 ENTRYPOINT ["/app/blocky"]

server/server.go

@@ -67,7 +67,9 @@ func NewServer(cfg *config.Config) (*Server, error) {
 	server.printConfiguration()
 
 	udpHandler.HandleFunc(".", server.OnRequest)
+	udpHandler.HandleFunc("healthcheck.blocky", server.OnHealthCheck)
 	tcpHandler.HandleFunc(".", server.OnRequest)
+	tcpHandler.HandleFunc("healthcheck.blocky", server.OnHealthCheck)
 
 	return &server, nil
 }
@@ -192,6 +194,17 @@ func (s *Server) OnRequest(w dns.ResponseWriter, request *dns.Msg) {
 	}
 }
 
+// Handler for docker healthcheck. Just returns OK code without delegating to resolver chain
+func (s *Server) OnHealthCheck(w dns.ResponseWriter, request *dns.Msg) {
+	resp := new(dns.Msg)
+	resp.SetReply(request)
+	resp.Rcode = dns.RcodeSuccess
+
+	if err := w.WriteMsg(resp); err != nil {
+		logger().Error("can't write message: ", err)
+	}
+}
+
 func resolveClientIP(addr net.Addr) net.IP {
 	var clientIP net.IP
 	if t, ok := addr.(*net.UDPAddr); ok {

server/server_test.go

@@ -155,6 +155,16 @@ var tests = []struct {
 			assert.Equal(t, "0.0.0.0", resp.Answer[0].(*dns.A).A.String())
 		},
 	},
+	{
+		// healthcheck
+		name:           "healthcheck",
+		mockClientName: "c1",
+		request:        util.NewMsgWithQuestion("healthcheck.blocky.", dns.TypeA),
+		respValidator: func(t *testing.T, resp *dns.Msg) {
+			assert.Equal(t, dns.RcodeSuccess, resp.Rcode)
+			assert.Empty(t, resp.Answer)
+		},
+	},
 }
 
 //nolint:funlen