Fix: increase max target length

Both Prometheus and Loki have relatiely large values for the maximum
length of label values (2048). We limit the legth of the labels we apply
to metrics and logs mostly to keep the UI usable. Allow for longer
target values, because this is actually in use.

Signed-off-by: Marcelo E. Magallon <marcelo.magallon@grafana.com>

pkg/pb/synthetic_monitoring/checks_extra.go

@@ -123,15 +123,16 @@ const (
 )
 
 const (
-	MaxMetricLabels        = 20  // Prometheus allows for 32 labels, but limit to 20.
-	MaxLogLabels           = 15  // Loki allows a maximum of 15 labels.
-	MaxCheckLabels         = 10  // Allow 10 user labels for checks,
-	MaxProbeLabels         = 3   // 3 for probes, leaving 7 for internal use.
-	MaxLabelValueLength    = 128 // Keep this number low so that the UI remains usable.
-	MaxPingPackets         = 10  // Allow 10 packets per ping.
-	MaxMultiHttpTargets    = 10  // Max targets per multi-http check.
-	MaxMultiHttpAssertions = 5   // Max assertions per multi-http target.
-	MaxMultiHttpVariables  = 5   // Max variables per multi-http target.
+	MaxMetricLabels          = 20   // Prometheus allows for 32 labels, but limit to 20.
+	MaxLogLabels             = 15   // Loki allows a maximum of 15 labels.
+	MaxCheckLabels           = 10   // Allow 10 user labels for checks,
+	MaxProbeLabels           = 3    // 3 for probes, leaving 7 for internal use.
+	maxValidLabelValueLength = 2048 // This is the actual max label value length.
+	MaxLabelValueLength      = 128  // Keep this number low so that the UI remains usable.
+	MaxPingPackets           = 10   // Allow 10 packets per ping.
+	MaxMultiHttpTargets      = 10   // Max targets per multi-http check.
+	MaxMultiHttpAssertions   = 5    // Max assertions per multi-http target.
+	MaxMultiHttpVariables    = 5    // Max variables per multi-http target.
 )
 
 type validatable interface {
@@ -265,7 +266,7 @@ func (c Check) Validate() error {
 
 func (c Check) validateTarget() error {
 	// All targets must be valid label values.
-	if err := validateLabelValue(c.Target); err != nil {
+	if len(c.Target) > maxValidLabelValueLength {
 		return ErrInvalidTargetValue
 	}