Use the correct equality operator for Prometheus Alerts

- Prometheus uses == (not =) for equality. Alerts that use single
  equal (=) result in a syntax error that silently fails to
  load any new alerts

-
  https://prometheus.io/docs/prometheus/latest/querying/operators/#comparison-binary-operators

ee/app/assets/javascripts/monitoring/components/alert_widget_form.vue

@@ -32,7 +32,7 @@ const SUBMIT_BUTTON_CLASS = {
 
 const OPERATORS = {
   greaterThan: '>',
-  equalTo: '=',
+  equalTo: '==',
   lessThan: '<',
 };
 

ee/app/models/prometheus_alert.rb

@@ -5,7 +5,7 @@ class PrometheusAlert < ApplicationRecord
 
   OPERATORS_MAP = {
     lt: "<",
-    eq: "=",
+    eq: "==",
     gt: ">"
   }.freeze
 

ee/changelogs/unreleased/use-correct-prometheus-equality-operator.yml

+---
+title: Fix equality operator for Prometheus alerts
+merge_request: 18919
+author:
+type: fixed

ee/spec/frontend/monitoring/alert_widget_spec.js

@@ -81,7 +81,7 @@ describe('AlertWidget', () => {
         expect(wrapper.find(GlLoadingIcon).isVisible()).toBe(true);
         expect(findWidgetForm().props('disabled')).toBe(true);
 
-        resolveReadAlert({ operator: '=', threshold: 42 });
+        resolveReadAlert({ operator: '==', threshold: 42 });
       })
       .then(() => waitForPromises())
       .then(() => {
@@ -123,7 +123,7 @@ describe('AlertWidget', () => {
           metricId,
         },
         'my/alert2.json': {
-          operator: '=',
+          operator: '==',
           threshold: 900,
           alert_path: 'my/alert2.json',
           metricId: '6',
@@ -163,7 +163,7 @@ describe('AlertWidget', () => {
 
   it('updates an alert with an appropriate handler', () => {
     const alertParams = { operator: '<', threshold: 4, alert_path: alertPath };
-    const newAlertParams = { operator: '=', threshold: 12 };
+    const newAlertParams = { operator: '==', threshold: 12 };
     mockReadAlert.mockResolvedValue(alertParams);
     mockUpdateAlert.mockResolvedValue({ ...alertParams, ...newAlertParams });
     createComponent({
@@ -171,7 +171,7 @@ describe('AlertWidget', () => {
       alertsToManage: {
         [alertPath]: {
           alert_path: alertPath,
-          operator: '=',
+          operator: '==',
           threshold: 12,
           metricId: '5',
         },

ee/spec/models/prometheus_alert_spec.rb

@@ -23,6 +23,13 @@ describe PrometheusAlert do
     end
   end
 
+  describe 'operators' do
+    it 'contains the correct equality operator' do
+      expect(described_class::OPERATORS_MAP.values).to include('==')
+      expect(described_class::OPERATORS_MAP.values).not_to include('=')
+    end
+  end
+
   describe 'associations' do
     it { is_expected.to belong_to(:project).required }
     it { is_expected.to belong_to(:environment).required }

ee/spec/services/projects/prometheus/alerts/update_service_spec.rb

@@ -17,7 +17,7 @@ describe Projects::Prometheus::Alerts::UpdateService do
     {
       environment_id: alert.environment_id,
       prometheus_metric_id: alert.prometheus_metric_id,
-      operator: '=',
+      operator: '==',
       threshold: 2.0
     }
   end