updated Dockerfile and renovate.json

Dockerfile

@@ -1,4 +1,10 @@
-FROM node:14.15.4-alpine
+ARG ARCH
+FROM amd64/alpine:3.12.3@sha256:074d3636ebda6dd446d0d00304c4454f468237fdacf08fb0eeac90bdbfa1bac7 AS base-amd64
+FROM arm32v7/alpine:3.12.3@sha256:299294be8699c1b323c137f972fd0aa5eaa4b95489c213091dcf46ef39b6c810 AS base-arm
+FROM arm64v8/alpine:3.12.3@sha256:549694ea68340c26d1d85c00039aa11ad835be279bfd475ff4284b705f92c24e AS base-arm64
+FROM base-${ARCH}
+
+RUN apk --no-cache add nodejs="12.20.1-r0"
 
 COPY dist/universal-statuspage /universal-statuspage
 

renovate.json

@@ -6,6 +6,20 @@
     "develop"
   ],
   "rangeStrategy": "bump",
+  "rebaseWhen": "behind-base-branch",
+  "regexManagers": [
+    {
+      "fileMatch": [
+        "^Dockerfile$"
+      ],
+      "matchStrings": [
+        "\\s+(?<depName>[a-z0-9\\-]+?)=\"(?<currentValue>.*?)\""
+      ],
+      "lookupNameTemplate": "alpine_3_12/{{{depName}}}",
+      "versioningTemplate": "loose",
+      "datasourceTemplate": "repology"
+    }
+  ],
   "packageRules": [
     {
       "managers": [
@@ -30,6 +44,22 @@
         "^jasmine"
       ],
       "enabled": false
+    },
+    {
+      "datasources": [
+        "repology"
+      ],
+      "groupName": [
+        "base dependencies"
+      ]
+    },
+    {
+      "datasources": [
+        "docker"
+      ],
+      "groupName": [
+        "docker images"
+      ]
     }
   ]
 }