Add deprecation warning for opencost external secret

Signed-off-by: Pete Wall <pete.wall@grafana.com>

charts/k8s-monitoring/ci/ci-values.yaml

@@ -100,7 +100,7 @@ opencost:
       extraEnv:
         INSECURE_SKIP_VERIFY: "true"
     prometheus:
-      secret_name: prometheus
+      existingSecretName: prometheus
       username_key: username
       password_key: password
       external:

charts/k8s-monitoring/templates/_deprecations.tpl

@@ -76,4 +76,25 @@ For more information, see https://github.com/grafana/k8s-monitoring-helm/tree/ma
   (index .Values.metrics "agent") }}
   {{ fail "\n\nAs of k8s-monitoring Chart version 1.0, Grafana Agent has been replaced with Grafana Alloy.\nThese sections in your values file will need to be renamed:\n  grafana-agent          --> alloy\n  grafana-agent-events   --> alloy-events\n  grafana-agent-logs     --> alloy-logs\n  grafana-agent-profiles --> alloy-profiles\n  metrics.agent          --> metrics.alloy\n\nFor more information, see https://github.com/grafana/k8s-monitoring-helm/tree/main/charts/k8s-monitoring#breaking-change-announcements" }}
 {{- end -}}
+
+{{/*
+v1.0.1: OpenCost changed how to reference an external secret
+
+As of k8s-monitoring Chart version 1.0.1, OpenCost changed how to reference an external secret.
+Please rename:
+opencost:
+  opencost:
+    prometheus:
+      secret_name: prometheus-k8s-monitoring
+To:
+opencost:
+  opencost:
+    prometheus:
+      existingSecretName: prometheus-k8s-monitoring
+
+For more information, see https://github.com/grafana/k8s-monitoring-helm/tree/main/charts/k8s-monitoring#breaking-change-announcements
+*/}}
+{{- if .Values.opencost.opencost.prometheus.secret_name }}
+  {{ fail "\n\nAs of k8s-monitoring Chart version 1.0.1, OpenCost changed how to reference an external secret.\nPlease rename:\nopencost:\n  opencost:\n    prometheus:\n      secret_name: prometheus-k8s-monitoring\nTo:\nopencost:\n  opencost:\n    prometheus:\n      existingSecretName: prometheus-k8s-monitoring\n\nFor more information, see https://github.com/grafana/k8s-monitoring-helm/tree/main/charts/k8s-monitoring#breaking-change-announcements" }}
+{{- end -}}
 {{- end -}}

tests/spec/deprecation-warning_spec.sh

@@ -68,6 +68,26 @@ These sections in your values file will need to be renamed:
   grafana-agent-profiles --> alloy-profiles
   metrics.agent          --> metrics.alloy
 
+For more information, see https://github.com/grafana/k8s-monitoring-helm/tree/main/charts/k8s-monitoring#breaking-change-announcements'
+    End
+  End
+
+  Describe 'Using older OpenCost secret_name in values file'
+    It 'prints a friendly error message'
+      When call helm template k8smon ../charts/k8s-monitoring -f "spec/fixtures/deprecated-opencost-secret_values.yaml"
+      The status should be failure
+      The error should include 'As of k8s-monitoring Chart version 1.0.1, OpenCost changed how to reference an external secret.
+Please rename:
+opencost:
+  opencost:
+    prometheus:
+      secret_name: prometheus-k8s-monitoring
+To:
+opencost:
+  opencost:
+    prometheus:
+      existingSecretName: prometheus-k8s-monitoring
+
 For more information, see https://github.com/grafana/k8s-monitoring-helm/tree/main/charts/k8s-monitoring#breaking-change-announcements'
     End
   End

tests/spec/fixtures/deprecated-opencost-secret_values.yaml

@@ -0,0 +1,23 @@
+cluster:
+  name: using-grafana-cloud-prometheus-component
+
+externalServices:
+  prometheus:
+    host: https://prometheus.example.com
+    basicAuth:
+      username: 12345
+      password: "It's a secret to everyone"
+  loki:
+    host: https://loki.example.com
+    basicAuth:
+      username: 12345
+      password: "It's a secret to everyone"
+
+opencost:
+  opencost:
+    prometheus:
+      secret_name: prometheus
+      username_key: username
+      password_key: password
+      external:
+        url: https://prometheus.example.com/api/prom