Show 503 page on collections under high load

This acknowledges "too many connections" and "max user connections" errors in MySQL and propagates the error up the chain so we can notify the user and return the correct HTTP code.
5 years ago · 0285a9b0bd
parent 06054a2cd7
commit 0285a9b0bd
5 changed files with 30 additions and 0 deletions
--- a/database-no-sqlite.go
+++ b/database-no-sqlite.go
@ -40,3 +40,13 @@ func (db *datastore) isIgnorableError(err error) bool {

 	return false
 }
+
+func (db *datastore) isHighLoadError(err error) bool {
+	if db.driverName == driverMySQL {
+		if mysqlErr, ok := err.(*mysql.MySQLError); ok {
+			return mysqlErr.Number == mySQLErrMaxUserConns || mysqlErr.Number == mySQLErrTooManyConns
+		}
+	}
+
+	return false
+}
--- a/database.go
+++ b/database.go
@ -39,6 +39,8 @@ import (
 const (
 	mySQLErrDuplicateKey = 1062
 	mySQLErrCollationMix = 1267
+	mySQLErrTooManyConns = 1040
+	mySQLErrMaxUserConns = 1203

 	driverMySQL  = "mysql"
 	driverSQLite = "sqlite3"
@ -793,6 +795,8 @@ func (db *datastore) GetCollectionBy(condition string, value interface{}) (*Coll
 	switch {
 	case err == sql.ErrNoRows:
 		return nil, impart.HTTPError{http.StatusNotFound, "Collection doesn't exist."}
+	case db.isHighLoadError(err):
+		return nil, ErrUnavailable
 	case err != nil:
 		log.Error("Failed selecting from collections: %v", err)
 		return nil, err
--- a/errors.go
+++ b/errors.go
@ -37,6 +37,8 @@ var (
 	ErrInternalGeneral       = impart.HTTPError{http.StatusInternalServerError, "The humans messed something up. They've been notified."}
 	ErrInternalCookieSession = impart.HTTPError{http.StatusInternalServerError, "Could not get cookie session."}

+	ErrUnavailable = impart.HTTPError{http.StatusServiceUnavailable, "Service temporarily unavailable due to high load."}
+
 	ErrCollectionNotFound     = impart.HTTPError{http.StatusNotFound, "Collection doesn't exist."}
 	ErrCollectionGone         = impart.HTTPError{http.StatusGone, "This blog was unpublished."}
 	ErrCollectionPageNotFound = impart.HTTPError{http.StatusNotFound, "Collection page doesn't exist."}
--- a/handle.go
+++ b/handle.go
@ -83,6 +83,7 @@ type ErrorPages struct {
 	NotFound            *template.Template
 	Gone                *template.Template
 	InternalServerError *template.Template
+	UnavailableError    *template.Template
 	Blank               *template.Template
 }

@ -94,6 +95,7 @@ func NewHandler(apper Apper) *Handler {
 			NotFound:            template.Must(template.New("").Parse("{{define \"base\"}}<html><head><title>404</title></head><body><p>Not found.</p></body></html>{{end}}")),
 			Gone:                template.Must(template.New("").Parse("{{define \"base\"}}<html><head><title>410</title></head><body><p>Gone.</p></body></html>{{end}}")),
 			InternalServerError: template.Must(template.New("").Parse("{{define \"base\"}}<html><head><title>500</title></head><body><p>Internal server error.</p></body></html>{{end}}")),
+			UnavailableError:    template.Must(template.New("").Parse("{{define \"base\"}}<html><head><title>503</title></head><body><p>Service is temporarily unavailable.</p></body></html>{{end}}")),
 			Blank:               template.Must(template.New("").Parse("{{define \"base\"}}<html><head><title>{{.Title}}</title></head><body><p>{{.Content}}</p></body></html>{{end}}")),
 		},
 		sessionStore: apper.App().SessionStore(),
@ -111,6 +113,7 @@ func NewWFHandler(apper Apper) *Handler {
 		NotFound:            pages["404-general.tmpl"],
 		Gone:                pages["410.tmpl"],
 		InternalServerError: pages["500.tmpl"],
+		UnavailableError:    pages["503.tmpl"],
 		Blank:               pages["blank.tmpl"],
 	})
 	return h
@ -763,6 +766,10 @@ func (h *Handler) handleHTTPError(w http.ResponseWriter, r *http.Request, err er
 			log.Info("handleHTTPErorr internal error render")
 			h.errors.InternalServerError.ExecuteTemplate(w, "base", pageForReq(h.app.App(), r))
 			return
+		} else if err.Status == http.StatusServiceUnavailable {
+			w.WriteHeader(err.Status)
+			h.errors.UnavailableError.ExecuteTemplate(w, "base", pageForReq(h.app.App(), r))
+			return
 		} else if err.Status == http.StatusAccepted {
 			impart.WriteSuccess(w, "", err.Status)
 			return
--- a/pages/503.tmpl
+++ b/pages/503.tmpl
@ -0,0 +1,7 @@
+{{define "head"}}<title>Temporarily Unavailable &mdash; {{.SiteMetaName}}</title>{{end}}
+{{define "content"}}
+		<div class="error-page">
+			<p class="msg">The words aren't coming to me. &#x1F5C5;</p>
+			<p>We couldn't serve this page due to high server load. This should only be temporary.</p>
+		</div>
+{{end}}