Do not interrupt querying readiness probes for plugins (#6975)

* Do not interrupt querying readiness probes for plugins

Signed-off-by: Gleb Kogtev <gleb.kogtev@gmail.com>

* Add monitor param for ready plugin

Signed-off-by: Gleb Kogtev <gleb.kogtev@gmail.com>

* Update ready docs

Signed-off-by: Gleb Kogtev <gleb.kogtev@gmail.com>

* Update ready docs

Signed-off-by: Gleb Kogtev <gleb.kogtev@gmail.com>

---------

Signed-off-by: Gleb Kogtev <gleb.kogtev@gmail.com>

plugin/ready/setup.go

@@ -11,10 +11,17 @@ import (
 func init() { plugin.Register("ready", setup) }
 
 func setup(c *caddy.Controller) error {
-	addr, err := parse(c)
+	addr, monType, err := parse(c)
 	if err != nil {
 		return plugin.Error("ready", err)
 	}
+
+	if monType == monitorTypeContinuously {
+		plugins.keepReadiness = true
+	} else {
+		plugins.keepReadiness = false
+	}
+
 	rd := &ready{Addr: addr}
 
 	uniqAddr.Set(addr, rd.onStartup)
@@ -48,12 +55,25 @@ func setup(c *caddy.Controller) error {
 	return nil
 }
 
-func parse(c *caddy.Controller) (string, error) {
+// monitorType represents the type of monitoring behavior for the readiness plugin.
+type monitorType string
+
+const (
+	// monitorTypeUntilReady indicates the monitoring should continue until the system is ready.
+	monitorTypeUntilReady monitorType = "until-ready"
+
+	// monitorTypeContinuously indicates the monitoring should continue indefinitely.
+	monitorTypeContinuously monitorType = "continuously"
+)
+
+func parse(c *caddy.Controller) (string, monitorType, error) {
 	addr := ":8181"
+	monType := monitorTypeUntilReady
+
 	i := 0
 	for c.Next() {
 		if i > 0 {
-			return "", plugin.ErrOnce
+			return "", "", plugin.ErrOnce
 		}
 		i++
 		args := c.RemainingArgs()
@@ -63,11 +83,38 @@ func parse(c *caddy.Controller) (string, error) {
 		case 1:
 			addr = args[0]
 			if _, _, e := net.SplitHostPort(addr); e != nil {
-				return "", e
+				return "", "", e
 			}
 		default:
-			return "", c.ArgErr()
+			return "", "", c.ArgErr()
+		}
+
+		for c.NextBlock() {
+			switch c.Val() {
+			case "monitor":
+				args := c.RemainingArgs()
+				if len(args) != 1 {
+					return "", "", c.ArgErr()
+				}
+
+				var err error
+				monType, err = parseMonitorType(c, args[0])
+				if err != nil {
+					return "", "", err
+				}
+			}
 		}
 	}
-	return addr, nil
+	return addr, monType, nil
+}
+
+func parseMonitorType(c *caddy.Controller, arg string) (monitorType, error) {
+	switch arg {
+	case "until-ready":
+		return monitorTypeUntilReady, nil
+	case "continuously":
+		return monitorTypeContinuously, nil
+	default:
+		return "", c.Errf("monitor type '%s' not supported", arg)
+	}
 }