Add null-safe hardening, probes and resources to patchmon

Third change of the same class (#99): an override written without
children is YAML null and replaced the whole default sub-tree, rendering
"securityContext: null" (unhardened container), a vanished probe or a
container without resource accounting - silently, while the workload
reports healthy.

The defaultedDict helper from #96 is adopted for both workloads, so an
empty block means "chart defaults apply" while an explicitly set value
still wins, including false and 0.

The server probes rebuild their Host header from ingress.domain via the
passed-in root context, because the 2.x server rejects requests whose
Host is neither loopback nor a CORS_ORIGIN host.

The schema types allow null for exactly these blocks, so schema and
helper agree instead of the schema rejecting what the helper absorbs.

Rendering with normal values is byte-identical to the previous version,
with and without the guacd sidecar.

patchmon/templates/_helpers.tpl

@@ -114,3 +114,210 @@ template-chart is the reference implementation.
 1
 {{- end -}}
 {{- end -}}
+
+{{/*
+Merge a user-supplied values sub-tree onto a dict of chart defaults so that a
+null / empty override falls back to the defaults instead of erasing them.
+
+Input: dict "defaults" <dict> "given" <dict|nil> "path" <string, optional
+values path used in error messages>. Output: YAML of the merged dict (consume
+it with fromYaml).
+
+Why this exists (issue #99): Helm merges values maps recursively, but an
+override key written without children — e.g. a leftover
+
+  securityContext:
+
+after deleting its last remaining sub-key — is YAML null and replaces the
+whole default sub-tree. The container then renders with "securityContext:
+null": no readOnlyRootFilesystem, no dropped capabilities, no
+allowPrivilegeEscalation: false. The workload starts and reports healthy while
+being unhardened, so nothing points at the mistake. The same shape erases a
+probe (it disappears) or the resources block (no requests, no computed
+limits). This helper defines the opposite semantics: an empty block means
+"chart defaults apply".
+
+Rules:
+  - a nil "given" is treated as an empty dict (all defaults apply).
+  - a key whose override value is null keeps the default (nulls never delete).
+  - a key present in both as a map is merged recursively, so a partially
+    filled block only overrides the keys it actually sets.
+  - a scalar override for a key the defaults define as a map is rejected with
+    a message naming the values path, instead of failing later with a template
+    field error.
+  - any other set value wins as given, including an explicit false or 0 —
+    Helm's "default" and sprig's "mergeOverwrite" would both swallow those
+    zero values, hence the explicit kindIs "invalid" nil check.
+  - keys only present in the override are passed through unchanged.
+
+NOTE: like the helpers above, this is duplicated into every chart's
+templates/_helpers.tpl with the chart's name as define prefix, because charts
+in this repo deliberately have no dependencies.
+*/}}
+{{- define "patchmon.defaultedDict" -}}
+{{- $defaults := .defaults | default dict -}}
+{{- $given := .given -}}
+{{- $path := .path | default "value" -}}
+{{- if kindIs "invalid" $given -}}
+{{- $given = dict -}}
+{{- end -}}
+{{- if not (kindIs "map" $given) -}}
+{{- fail (printf "%s must be a mapping or null, got %s (%v)" $path (kindOf $given) $given) -}}
+{{- end -}}
+{{- $out := deepCopy $defaults -}}
+{{- range $key, $value := $given -}}
+{{- if not (kindIs "invalid" $value) -}}
+{{- $default := index $defaults $key -}}
+{{- if and (kindIs "map" $value) (kindIs "map" $default) -}}
+{{- $_ := set $out $key (fromYaml (include "patchmon.defaultedDict" (dict "defaults" $default "given" $value "path" (printf "%s.%s" $path $key)))) -}}
+{{- else if kindIs "map" $default -}}
+{{- fail (printf "%s.%s must be a mapping or null, got %s (%v)" $path $key (kindOf $value) $value) -}}
+{{- else -}}
+{{- $_ := set $out $key $value -}}
+{{- end -}}
+{{- end -}}
+{{- end -}}
+{{- toYaml $out -}}
+{{- end -}}
+
+{{/*
+Pick one sub-block out of a values block that may itself be null.
+
+Input: dict "block" <dict|nil> "key" <string> "path" <string>.
+Returns YAML of dict "value" <the sub-block, may be nil>, after rejecting a
+non-mapping block with a message that names the values path. Needed because
+".Values.patchmon.<workload>.securityContext" can itself be erased.
+*/}}
+{{- define "patchmon.subBlock" -}}
+{{- $block := .block -}}
+{{- if kindIs "invalid" $block -}}
+{{- $block = dict -}}
+{{- end -}}
+{{- if not (kindIs "map" $block) -}}
+{{- fail (printf "%s must be a mapping or null, got %s (%v)" .path (kindOf $block) $block) -}}
+{{- end -}}
+{{- toYaml (dict "value" (index $block .key)) -}}
+{{- end -}}
+
+{{/*
+The effective security contexts, probes and resources of both workloads
+(issue #99).
+
+The defaults below MUST stay in sync with the corresponding blocks in
+values.yaml, which stays the documented, user-facing place for them; this copy
+is only the fallback for the case where an override has erased the block.
+
+The server probes carry a Host header, because the 2.x server rejects requests
+whose Host is neither loopback nor a CORS_ORIGIN host. The default is built
+from .Values.ingress.domain via the passed-in root context, so the probe
+helpers take dict "given" <block|nil> "root" $.
+*/}}
+{{- define "patchmon.server.podSecurityContext" -}}
+{{- $given := (fromYaml (include "patchmon.subBlock" (dict "block" . "key" "pod" "path" "patchmon.server.securityContext"))).value -}}
+{{- $defaults := dict
+      "runAsNonRoot" true
+      "runAsUser" 65532
+      "runAsGroup" 65532 -}}
+{{- include "patchmon.defaultedDict" (dict "defaults" $defaults "given" $given "path" "patchmon.server.securityContext.pod") -}}
+{{- end -}}
+
+{{- define "patchmon.server.containerSecurityContext" -}}
+{{- $given := (fromYaml (include "patchmon.subBlock" (dict "block" . "key" "container" "path" "patchmon.server.securityContext"))).value -}}
+{{- $defaults := dict
+      "allowPrivilegeEscalation" false
+      "readOnlyRootFilesystem" true
+      "runAsNonRoot" true
+      "capabilities" (dict "drop" (list "ALL")) -}}
+{{- include "patchmon.defaultedDict" (dict "defaults" $defaults "given" $given "path" "patchmon.server.securityContext.container") -}}
+{{- end -}}
+
+{{- define "patchmon.guacd.containerSecurityContext" -}}
+{{- $given := (fromYaml (include "patchmon.subBlock" (dict "block" . "key" "container" "path" "patchmon.guacd.securityContext"))).value -}}
+{{- $defaults := dict
+      "allowPrivilegeEscalation" false
+      "readOnlyRootFilesystem" true
+      "runAsNonRoot" true
+      "runAsUser" 1000
+      "runAsGroup" 1000
+      "capabilities" (dict "drop" (list "ALL")) -}}
+{{- include "patchmon.defaultedDict" (dict "defaults" $defaults "given" $given "path" "patchmon.guacd.securityContext.container") -}}
+{{- end -}}
+
+{{- define "patchmon.server.httpGet" -}}
+{{- dict "path" "/health" "port" 3000 "httpHeaders" (list (dict "name" "Host" "value" (.root.Values.ingress.domain | default ""))) | toYaml -}}
+{{- end -}}
+
+{{- define "patchmon.server.livenessProbe" -}}
+{{- $defaults := dict
+      "httpGet" (fromYaml (include "patchmon.server.httpGet" .))
+      "periodSeconds" 10
+      "timeoutSeconds" 5
+      "failureThreshold" 3 -}}
+{{- include "patchmon.defaultedDict" (dict "defaults" $defaults "given" .given "path" "patchmon.server.livenessProbe") -}}
+{{- end -}}
+
+{{- define "patchmon.server.readinessProbe" -}}
+{{- $defaults := dict
+      "httpGet" (fromYaml (include "patchmon.server.httpGet" .))
+      "periodSeconds" 10
+      "timeoutSeconds" 5
+      "failureThreshold" 3 -}}
+{{- include "patchmon.defaultedDict" (dict "defaults" $defaults "given" .given "path" "patchmon.server.readinessProbe") -}}
+{{- end -}}
+
+{{- define "patchmon.server.startupProbe" -}}
+{{- $defaults := dict
+      "httpGet" (fromYaml (include "patchmon.server.httpGet" .))
+      "periodSeconds" 10
+      "timeoutSeconds" 5
+      "failureThreshold" 60 -}}
+{{- include "patchmon.defaultedDict" (dict "defaults" $defaults "given" .given "path" "patchmon.server.startupProbe") -}}
+{{- end -}}
+
+{{- define "patchmon.guacd.livenessProbe" -}}
+{{- $defaults := dict
+      "tcpSocket" (dict "port" 4822)
+      "periodSeconds" 10
+      "timeoutSeconds" 5
+      "failureThreshold" 3 -}}
+{{- include "patchmon.defaultedDict" (dict "defaults" $defaults "given" . "path" "patchmon.guacd.livenessProbe") -}}
+{{- end -}}
+
+{{- define "patchmon.guacd.readinessProbe" -}}
+{{- $defaults := dict
+      "tcpSocket" (dict "port" 4822)
+      "periodSeconds" 10
+      "timeoutSeconds" 5
+      "failureThreshold" 3 -}}
+{{- include "patchmon.defaultedDict" (dict "defaults" $defaults "given" . "path" "patchmon.guacd.readinessProbe") -}}
+{{- end -}}
+
+{{- define "patchmon.guacd.startupProbe" -}}
+{{- $defaults := dict
+      "tcpSocket" (dict "port" 4822)
+      "periodSeconds" 5
+      "timeoutSeconds" 5
+      "failureThreshold" 30 -}}
+{{- include "patchmon.defaultedDict" (dict "defaults" $defaults "given" . "path" "patchmon.guacd.startupProbe") -}}
+{{- end -}}
+
+{{/*
+The effective resources blocks, fed into the resources helper above so that an
+erased "resources:" still yields the chart's requests and computed limits
+instead of a container without any resource accounting.
+*/}}
+{{- define "patchmon.server.effectiveResources" -}}
+{{- $defaults := dict
+      "limitFactor" 3
+      "requests" (dict "cpu" 0.1 "memory" "256Mi" "ephemeral-storage" "10Mi") -}}
+{{- $merged := fromYaml (include "patchmon.defaultedDict" (dict "defaults" $defaults "given" . "path" "patchmon.server.resources")) -}}
+{{- include "patchmon.resources" $merged -}}
+{{- end -}}
+
+{{- define "patchmon.guacd.effectiveResources" -}}
+{{- $defaults := dict
+      "limitFactor" 3
+      "requests" (dict "cpu" 0.05 "memory" "64Mi" "ephemeral-storage" "10Mi") -}}
+{{- $merged := fromYaml (include "patchmon.defaultedDict" (dict "defaults" $defaults "given" . "path" "patchmon.guacd.resources")) -}}
+{{- include "patchmon.resources" $merged -}}
+{{- end -}}

patchmon/templates/patchmon.deployment.yaml

@@ -23,13 +23,13 @@ spec:
       # for the same reason).
       hostname: {{ .Release.Name }}-{{ .Chart.Name }}-server
       securityContext:
-        {{- toYaml .Values.patchmon.server.securityContext.pod | nindent 8 }}
+        {{- include "patchmon.server.podSecurityContext" .Values.patchmon.server.securityContext | nindent 8 }}
       containers:
         - name: {{ .Release.Name }}-{{ .Chart.Name }}-server
           image: "ghcr.io/patchmon/patchmon-server:{{ .Chart.AppVersion }}"
           imagePullPolicy: IfNotPresent
           securityContext:
-            {{- toYaml .Values.patchmon.server.securityContext.container | nindent 12 }}
+            {{- include "patchmon.server.containerSecurityContext" .Values.patchmon.server.securityContext | nindent 12 }}
           ports:
             - containerPort: 3000
               protocol: TCP
@@ -166,13 +166,13 @@ spec:
           # Probe values are rendered through tpl (see values.yaml for the
           # defaults and why the probes send a Host header).
           livenessProbe:
-            {{- tpl (toYaml .Values.patchmon.server.livenessProbe) . | nindent 12 }}
+            {{- tpl (include "patchmon.server.livenessProbe" (dict "given" .Values.patchmon.server.livenessProbe "root" $)) . | nindent 12 }}
           readinessProbe:
-            {{- tpl (toYaml .Values.patchmon.server.readinessProbe) . | nindent 12 }}
+            {{- tpl (include "patchmon.server.readinessProbe" (dict "given" .Values.patchmon.server.readinessProbe "root" $)) . | nindent 12 }}
           startupProbe:
-            {{- tpl (toYaml .Values.patchmon.server.startupProbe) . | nindent 12 }}
+            {{- tpl (include "patchmon.server.startupProbe" (dict "given" .Values.patchmon.server.startupProbe "root" $)) . | nindent 12 }}
           resources:
-            {{- include "patchmon.resources" .Values.patchmon.server.resources | nindent 12 }}
+            {{- include "patchmon.server.effectiveResources" .Values.patchmon.server.resources | nindent 12 }}
           volumeMounts:
             # The image is stateless, but the Go server needs a writable /tmp
             # for scratch files with a read-only root filesystem.
@@ -206,19 +206,19 @@ spec:
             {{- end }}
           {{- end }}
           securityContext:
-            {{- toYaml .Values.patchmon.guacd.securityContext.container | nindent 12 }}
+            {{- include "patchmon.guacd.containerSecurityContext" .Values.patchmon.guacd.securityContext | nindent 12 }}
           ports:
             - containerPort: 4822
               protocol: TCP
               name: guacd
           livenessProbe:
-            {{- tpl (toYaml .Values.patchmon.guacd.livenessProbe) . | nindent 12 }}
+            {{- tpl (include "patchmon.guacd.livenessProbe" .Values.patchmon.guacd.livenessProbe) . | nindent 12 }}
           readinessProbe:
-            {{- tpl (toYaml .Values.patchmon.guacd.readinessProbe) . | nindent 12 }}
+            {{- tpl (include "patchmon.guacd.readinessProbe" .Values.patchmon.guacd.readinessProbe) . | nindent 12 }}
           startupProbe:
-            {{- tpl (toYaml .Values.patchmon.guacd.startupProbe) . | nindent 12 }}
+            {{- tpl (include "patchmon.guacd.startupProbe" .Values.patchmon.guacd.startupProbe) . | nindent 12 }}
           resources:
-            {{- include "patchmon.resources" .Values.patchmon.guacd.resources | nindent 12 }}
+            {{- include "patchmon.guacd.effectiveResources" .Values.patchmon.guacd.resources | nindent 12 }}
           volumeMounts:
             - name: guacd-tmp
               mountPath: /tmp