feat: set read-only root filesystem at container level

Change the securityContext field of the Reloader container if
reloader.readOnlyFilesystem is set to true. The change takes effect even
if not container securityContext is defined.

Closes #339.

deployments/kubernetes/chart/reloader/templates/deployment.yaml

@@ -148,9 +148,13 @@ spec:
           periodSeconds: {{ .Values.reloader.deployment.readinessProbe.periodSeconds | default "10" }}
           successThreshold: {{ .Values.reloader.deployment.readinessProbe.successThreshold | default "1" }}
 
-      {{- with .Values.reloader.deployment.containerSecurityContext }}
-        securityContext: {{ toYaml . | nindent 10 }}
-      {{- end }}
+        {{- $containerSecurityContext := .Values.reloader.deployment.containerSecurityContext | default dict }}
+        {{- if .Values.reloader.readOnlyRootFilesystem }}
+          {{- $_ := set $containerSecurityContext "readOnlyRootFilesystem" true }}
+        {{- end }}
+
+        securityContext:
+          {{- toYaml $containerSecurityContext | nindent 10 }}
 
       {{- if eq .Values.reloader.readOnlyRootFileSystem true }}
         volumeMounts:

deployments/kubernetes/chart/reloader/tests/deployment_test.yaml

@@ -0,0 +1,50 @@
+suite: Deployment
+
+templates:
+  - deployment.yaml
+
+tests:
+  - it: sets readOnlyRootFilesystem in container securityContext when reloader.readOnlyRootFilesystem is true
+    set:
+      reloader:
+        readOnlyRootFilesystem: true
+        deployment:
+          containerSecurityContext:
+            readOnlyRootFilesystem: false
+    asserts:
+      - equal:
+          path: spec.template.spec.containers[0].securityContext.readOnlyRootFilesystem
+          value: true
+
+  - it: sets readOnlyRootFilesystem in container securityContext even if reloader.deployment.containerSecurityContext is null
+    set:
+      reloader:
+        readOnlyRootFilesystem: true
+        deployment:
+          containerSecurityContext: null
+    asserts:
+      - equal:
+          path: spec.template.spec.containers[0].securityContext.readOnlyRootFilesystem
+          value: true
+
+  - it: does not override readOnlyRootFilesystem in container securityContext based on reloader.readOnlyRootFilesystem
+    set:
+      reloader:
+        readOnlyRootFilesystem: false
+        deployment:
+          containerSecurityContext:
+            readOnlyRootFilesystem: true
+    asserts:
+      - equal:
+          path: spec.template.spec.containers[0].securityContext.readOnlyRootFilesystem
+          value: true
+
+  - it: template is still valid with no defined containerSecurityContext
+    set:
+      reloader:
+        readOnlyRootFilesystem: false
+        deployment:
+          containerSecurityContext: null
+    asserts:
+      - isEmpty:
+          path: spec.template.spec.containers[0].securityContext