feat(mastodon): Add proper zero downtime db migrations

This patch implements the full zero downtime upgrade path recommended by
upstream into the helm chart, which should provide a smooth experience
for upgrades.

charts/mastodon/templates/job-db-migrate.yaml

@@ -5,7 +5,7 @@ metadata:
   labels:
     {{- include "mastodon.labels" . | nindent 4 }}
   annotations:
-    "helm.sh/hook": post-install,pre-upgrade
+    "helm.sh/hook": post-install,post-upgrade
     "helm.sh/hook-delete-policy": before-hook-creation,hook-succeeded
     "helm.sh/hook-weight": "-2"
 spec:

charts/mastodon/templates/job-db-pre-migrate.yaml

+apiVersion: batch/v1
+kind: Job
+metadata:
+  name: {{ include "mastodon.fullname" . }}-db-migrate
+  labels:
+    {{- include "mastodon.labels" . | nindent 4 }}
+  annotations:
+    "helm.sh/hook": pre-upgrade
+    "helm.sh/hook-delete-policy": before-hook-creation,hook-succeeded
+    "helm.sh/hook-weight": "-2"
+spec:
+  template:
+    metadata:
+      name: {{ include "mastodon.fullname" . }}-db-migrate
+      {{- with .Values.jobAnnotations }}
+      annotations:
+        {{- toYaml . | nindent 8 }}
+      {{- end }}
+    spec:
+      restartPolicy: Never
+      {{- with (default .Values.affinity .Values.mastodon.web.affinity) }}
+      affinity:
+        {{- toYaml . | nindent 8 }}
+      {{- end }}
+      {{- if (not .Values.mastodon.s3.enabled) }}
+      volumes:
+        - name: assets
+          persistentVolumeClaim:
+            claimName: {{ template "mastodon.fullname" . }}-assets
+        - name: system
+          persistentVolumeClaim:
+            claimName: {{ template "mastodon.fullname" . }}-system
+      {{- end }}
+      containers:
+        - name: {{ include "mastodon.fullname" . }}-db-migrate
+          image: "{{ .Values.image.repository }}:{{ .Values.image.tag | default .Chart.AppVersion }}"
+          imagePullPolicy: {{ .Values.image.pullPolicy }}
+          command:
+            - bundle
+            - exec
+            - rake
+            - db:migrate
+          envFrom:
+            - configMapRef:
+                name: {{ include "mastodon.fullname" . }}-env
+            - secretRef:
+                name: {{ template "mastodon.secretName" . }}
+          env:
+            - name: "DB_PASS"
+              valueFrom:
+                secretKeyRef:
+                  name: {{ template "mastodon.postgresql.secretName" . }}
+                  key: password
+            - name: "REDIS_PASSWORD"
+              valueFrom:
+                secretKeyRef:
+                  name: {{ template "mastodon.redis.secretName" . }}
+                  key: redis-password
+            - name: "PORT"
+              value: {{ .Values.mastodon.web.port | quote }}
+            - name: SKIP_POST_DEPLOYMENT_MIGRATIONS
+              value: "true"
+          {{- if (not .Values.mastodon.s3.enabled) }}
+          volumeMounts:
+            - name: assets
+              mountPath: /opt/mastodon/public/assets
+            - name: system
+              mountPath: /opt/mastodon/public/system
+          {{- end }}