Alerting: Add rule_limit parameter to the list rules API (#114055)

pkg/services/ngalert/api/prometheus/api_prometheus.go

@@ -492,10 +492,22 @@ func PrepareRuleGroupStatusesV2(log log.Logger, store ListAlertRulesStoreV2, opt
 		ruleType = ngmodels.RuleTypeFilterAll
 	}
 
+	// Pagination limits
+	//
+	// group_limit: Maximum number of rule groups to return
+	//   - Returns exactly this many groups or fewer if not enough exist
+	//
+	// rule_limit: Maximum number of rules to return across all groups
+	//   - Returns complete groups until total rules meets or exceeds this limit
+	//   - May exceed the rule limit if needed to include the final complete group
+	//   - Example: rule_limit=15 with groups of [10, 10, 10] rules returns first 2 groups, 20 rules total
+	//
+	// When both limits are specified, whichever limit is reached first takes precedence.
 	maxGroups := getInt64WithDefault(opts.Query, "group_limit", -1)
+	maxRules := getInt64WithDefault(opts.Query, "rule_limit", -1)
 	nextToken := opts.Query.Get("group_next_token")
 
-	if maxGroups == 0 {
+	if maxGroups == 0 || maxRules == 0 {
 		return ruleResponse
 	}
 
@@ -512,6 +524,7 @@ func PrepareRuleGroupStatusesV2(log log.Logger, store ListAlertRulesStoreV2, opt
 		},
 		RuleType:      ruleType,
 		Limit:         maxGroups,
+		RuleLimit:     maxRules,
 		ContinueToken: nextToken,
 	}
 	ruleList, continueToken, err := store.ListAlertRulesByGroup(opts.Ctx, &byGroupQuery)
@@ -557,7 +570,7 @@ func PrepareRuleGroupStatusesV2(log log.Logger, store ListAlertRulesStoreV2, opt
 	ruleResponse.Data.NextToken = continueToken
 
 	// Only return Totals if there is no pagination
-	if maxGroups == -1 {
+	if maxGroups == -1 && maxRules == -1 {
 		ruleResponse.Data.Totals = rulesTotals
 	}