hack: inject jinja after helm template

This hack is required to bypass the fact that
dumping unquoted special characters (e.g `{%`) does not work with
the render script.

If we try to escape this special character, we end up with type(str) always
and in a special condition, we need replicas count to be of type(int)

charts/prometheus-operator.yaml

@@ -9,7 +9,7 @@ commonLabels:
 alertmanager:
   alertmanagerSpec:
     image:
-      repository: '''{%- endraw -%}{{ build_image_name("alertmanager", False) }}{%- raw -%}'''
+      repository: '__image__(alertmanager)'
 
     nodeSelector:
       node-role.kubernetes.io/infra: ''
@@ -24,6 +24,8 @@ alertmanager:
         operator: 'Exists'
         effect: 'NoSchedule'
 
+    replicas: '__var__(alertmanager.spec.deployment.replicas)'
+
     storage:
       volumeClaimTemplate:
         spec:
@@ -56,22 +58,22 @@ prometheusOperator:
       effect: 'NoSchedule'
 
   image:
-    repository: '{%- endraw -%}{{ build_image_name(\"prometheus-operator\", False) }}{%- raw -%}'
+    repository: '__image__(prometheus-operator)'
 
   configmapReloadImage:
-    repository: '{%- endraw -%}{{ build_image_name("configmap-reload", False) }}{%- raw -%}'
+    repository: '__image__(configmap-reload)'
 
   prometheusConfigReloaderImage:
-    repository: '{%- endraw -%}{{ build_image_name("prometheus-config-reloader", False) }}{%- raw -%}'
+    repository: '__image__(prometheus-config-reloader)'
 
   hyperkubeImage:
-    repository: '''{%- endraw -%}{{ build_image_name("hyperkube", False) }}{%- raw -%}'''
+    repository: '__image__(hyperkube)'
 
 
 prometheus:
   prometheusSpec:
     image:
-      repository: '''{%- endraw -%}{{ build_image_name("prometheus", False) }}{%- raw -%}'''
+      repository: '__image__(prometheus)'
 
     tolerations:
       - key: 'node-role.kubernetes.io/bootstrap'
@@ -81,6 +83,8 @@ prometheus:
         operator: 'Exists'
         effect: 'NoSchedule'
 
+    replicas: '__var__(prometheus.spec.deployment.replicas)'
+
     nodeSelector:
       node-role.kubernetes.io/infra: ''
 
@@ -102,10 +106,10 @@ grafana:
   adminPassword: admin
 
   image:
-    repository: '{%- endraw -%}{{ build_image_name(\"grafana\", False) }}{%- raw -%}'
+    repository: '__image__(grafana)'
 
   sidecar:
-    image: '{%- endraw -%}{{ build_image_name(\"k8s-sidecar\", False) }}{%- raw -%}:0.1.20'
+    image: '__image__(k8s-sidecar):0.1.20'
 
   nodeSelector:
     node-role.kubernetes.io/infra: ''
@@ -118,6 +122,9 @@ grafana:
       operator: 'Exists'
       effect: 'NoSchedule'
 
+  replicas: '__var__(grafana.spec.deployment.replicas)'
+
+
   ingress:
     enabled: true
     annotations:
@@ -140,7 +147,7 @@ grafana:
 
 kube-state-metrics:
   image:
-    repository: '{%- endraw -%}{{ build_image_name(\"kube-state-metrics\", False) }}{%- raw -%}'
+    repository: '__image__(kube-state-metrics)'
 
   nodeSelector:
     node-role.kubernetes.io/infra: ''
@@ -156,7 +163,7 @@ kube-state-metrics:
 
 prometheus-node-exporter:
   image:
-    repository: '{%- endraw -%}{{ build_image_name(\"node-exporter\", False) }}{%- raw -%}'
+    repository: '__image__(node-exporter)'
 
 
 kubeEtcd:

charts/render.py

@@ -16,9 +16,18 @@
   `app.kubernetes.io/managed-by` to `salt`, and copy any `app` and
   `component` fields to the canonical `app.kubernetes.io/name` and
   `app.kubernetes.io/component` fields
+- Replace YAML-safe special strings (used in Helm values definitions) with the
+  appropriate Jinja syntax. Supports:
+    - "__var__(<varname>)", to replace with "{{ <varname> }}" (useful when
+      retrieving variables from service configuration ConfigMaps)
+    - "__image__(<imgname>)", to replace with
+      "{{ build_image_name("<imgname>", False) }}"
+    - "__full_image__(<imgname>)", to replace with
+      "{{ build_image_name("<imgname>") }}"
 '''
 
 import argparse
+import io
 import re
 import sys
 import subprocess
@@ -28,18 +37,18 @@
 from yaml.representer import SafeRepresenter
 
 
-START_BLOCK = '''
+START_BLOCK = """
 #!jinja | metalk8s_kubernetes
-{{%- from "metalk8s/repo/macro.sls" import build_image_name with context %}}
 
+{{%- from "metalk8s/repo/macro.sls" import build_image_name with context %}}
 {configlines}
 
 {{% raw %}}
-'''
+"""
 
-END_BLOCK = '''
+END_BLOCK = """
 {% endraw %}
-'''
+"""
 
 
 def fixup_metadata(namespace, doc):
@@ -117,6 +126,31 @@ def keep_doc(doc):
     return True
 
 
+def replace_magic_strings(rendered_yaml):
+    # Handle __var__
+    result = re.sub(
+        r'__var__\((?P<varname>[\w\-_]+(?:\.[\w\-_]+)*)\)',
+        r'{% endraw -%}{{ \g<varname> }}{%- raw %}',
+        rendered_yaml,
+    )
+
+    # Handle __image__
+    result = re.sub(
+        r'__image__\((?P<imgname>[\w\-]+)\)',
+        r'{% endraw -%}{{ build_image_name("\g<imgname>", False) }}{%- raw %}',
+        result,
+    )
+
+    # Handle __full_image__ (include version tag in the rendered name)
+    result = re.sub(
+        r'__full_image__\((?P<imgname>[\w\-]+)\)',
+        r'{% endraw -%}{{ build_image_name("\g<imgname>") }}{%- raw %}',
+        result,
+    )
+
+    return result
+
+
 def main():
     parser = argparse.ArgumentParser()
     parser.add_argument('name', help="Denotes the name of the chart")
@@ -175,13 +209,17 @@ def main():
     )
     sys.stdout.write('\n')
 
+    stream = io.StringIO()
     yaml.safe_dump_all(
         (fixup(doc)
             for doc in yaml.safe_load_all(template)
             if keep_doc(doc)),
-        sys.stdout,
+        stream,
         default_flow_style=False,
     )
+    stream.seek(0)
+
+    sys.stdout.write(replace_magic_strings(stream.read()))
 
     sys.stdout.write(END_BLOCK)