fix(observability-proxy): require a range and bucket count the step cap fits

The step is capped at a third of the maximum range so that vlselect's
alignment to whole steps cannot widen the window past that range. With
fewer than three buckets, or a range under three seconds, the minimum
step exceeds that cap and the bound no longer holds, so such settings
are refused at startup.

Assisted-by: LLM
Signed-off-by: ZverGuy <maximbel2003@gmail.com>

cmd/observability-proxy/main.go

@@ -96,8 +96,12 @@ func parseFlags(args []string) (options, error) {
 		return o, errors.New("--cluster-domain must not be empty")
 	case o.logs.DefaultRange <= 0 || o.logs.MaxRange < o.logs.DefaultRange:
 		return o, errors.New("--logs-default-range must be positive and not above --logs-max-range")
-	case o.logs.MaxBuckets <= 0:
-		return o, errors.New("--logs-max-buckets must be positive")
+	// Below three buckets, or a range under three seconds, the step cap
+	// that keeps vlselect's step alignment inside the range cannot hold.
+	case o.logs.MaxBuckets < 3:
+		return o, errors.New("--logs-max-buckets must be at least 3")
+	case o.logs.MaxRange < 3*time.Second:
+		return o, errors.New("--logs-max-range must be at least 3s")
 	case o.logs.DefaultLimit <= 0 || o.logs.MaxLimit < o.logs.DefaultLimit:
 		return o, errors.New("--logs-default-limit must be positive and not above --logs-max-limit")
 	case o.logs.MaxTailResume < 0:

cmd/observability-proxy/main_test.go

@@ -49,7 +49,9 @@ func TestParseFlagsInvalid(t *testing.T) {
 		{"--root-tenant="},
 		{"--cluster-domain="},
 		{"--logs-default-range=48h", "--logs-max-range=24h"},
-		{"--logs-max-buckets=0"},
+		{"--logs-max-buckets=2"},
+		{"--logs-max-range=2s", "--logs-default-range=1s"},
+		{"--shutdown-timeout=-1s"},
 		{"--logs-default-limit=0"},
 		{"--logs-default-limit=100", "--logs-max-limit=10"},
 		{"--logs-max-tail-resume=-1m"},