logging: Soft start for net writer (close #5520)

If enabled and there is an error when opening the net writer, ignore the
error and report it along with subsequent logs to stderr.

1 files changed, 26 insertions, 6 deletions

diff --git a/modules/logging/netwriter.go b/modules/logging/netwriter.go
index 5a6cf39..954a09b 100644
--- a/modules/logging/netwriter.go
+++ b/modules/logging/netwriter.go
@@ -40,6 +40,11 @@ type NetWriter struct {
 	// The timeout to wait while connecting to the socket.
 	DialTimeout caddy.Duration `json:"dial_timeout,omitempty"`
 
+	// If enabled, allow connections errors when first opening the
+	// writer. The error and subsequent log entries will be reported
+	// to stderr instead until a connection can be re-established.
+	SoftStart bool `json:"soft_start,omitempty"`
+
 	addr caddy.NetworkAddress
 }
 
@@ -92,7 +97,9 @@ func (nw NetWriter) OpenWriter() (io.WriteCloser, error) {
 	}
 	conn, err := reconn.dial()
 	if err != nil {
-		return nil, err
+		// don't block config load if remote is down or some other external problem;
+		// we can dump logs to stderr for now (see issue #5520)
+		fmt.Fprintf(os.Stderr, "[ERROR] net log writer failed to connect: %v (will retry connection and print errors here in the meantime)\n", err)
 	}
 	reconn.connMu.Lock()
 	reconn.Conn = conn
@@ -104,6 +111,7 @@ func (nw NetWriter) OpenWriter() (io.WriteCloser, error) {
 //
 //	net <address> {
 //	    dial_timeout <duration>
+//	    soft_start
 //	}
 func (nw *NetWriter) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 	for d.Next() {
@@ -128,6 +136,12 @@ func (nw *NetWriter) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 					return d.ArgErr()
 				}
 				nw.DialTimeout = caddy.Duration(timeout)
+
+			case "soft_start":
+				if d.NextArg() {
+					return d.ArgErr()
+				}
+				nw.SoftStart = true
 			}
 		}
 	}
@@ -151,8 +165,10 @@ func (reconn *redialerConn) Write(b []byte) (n int, err error) {
 	reconn.connMu.RLock()
 	conn := reconn.Conn
 	reconn.connMu.RUnlock()
-	if n, err = conn.Write(b); err == nil {
-		return
+	if conn != nil {
+		if n, err = conn.Write(b); err == nil {
+			return
+		}
 	}
 
 	// problem with the connection - lock it and try to fix it
@@ -161,8 +177,10 @@ func (reconn *redialerConn) Write(b []byte) (n int, err error) {
 
 	// if multiple concurrent writes failed on the same broken conn, then
 	// one of them might have already re-dialed by now; try writing again
-	if n, err = reconn.Conn.Write(b); err == nil {
-		return
+	if reconn.Conn != nil {
+		if n, err = reconn.Conn.Write(b); err == nil {
+			return
+		}
 	}
 
 	// there's still a problem, so try to re-attempt dialing the socket
@@ -178,7 +196,9 @@ func (reconn *redialerConn) Write(b []byte) (n int, err error) {
 			return
 		}
 		if n, err = conn2.Write(b); err == nil {
-			reconn.Conn.Close()
+			if reconn.Conn != nil {
+				reconn.Conn.Close()
+			}
 			reconn.Conn = conn2
 		}
 	} else {