sort targets in disco endpoint

main.go

···
 			// SingleHostReverseProxy for each upstream.
 			rpx = make(map[string]http.Handler)
 
-			// targets returned by http_sd discovery endpoint.
+			// targets returned by the http_sd discovery endpoint.
 			targets []string
 		)
 		for _, u := range ups {

tsproxy.go

···
 	"net/http"
 	"net/http/httputil"
 	"net/url"
+	"sort"
 
 	"golang.org/x/exp/slog"
 	"tailscale.com/client/tailscale/apitype"
···
 }
 
 func tsReverseProxy(rpx map[string]http.Handler, metrics http.Handler, targets []string, self string) http.Handler {
+	sort.Strings(targets)
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.TLS == nil {
 			http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

tsproxy_test.go

···
 		},
 		{
 			name: "self service discovery",
-			h:    tsReverseProxy(nil, nil, []string{"localhost:8000"}, "example.com"),
+			h:    tsReverseProxy(nil, nil, []string{"zzz:80", "localhost:8000"}, "example.com"),
 			req:  &http.Request{RequestURI: "/sd", TLS: &tls.ConnectionState{ServerName: "example.com"}},
-			want: &http.Response{StatusCode: http.StatusOK, Header: http.Header{"Content-Type": []string{`application/json; charset=utf-8`}}, Body: io.NopCloser(bytes.NewReader([]byte(`[{"targets":["localhost:8000"]}]`)))},
+			want: &http.Response{StatusCode: http.StatusOK, Header: http.Header{"Content-Type": []string{`application/json; charset=utf-8`}}, Body: io.NopCloser(bytes.NewReader([]byte(`[{"targets":["localhost:8000","zzz:80"]}]`)))},
 		},
 	} {
 		tc := tc