diff --git a/Dockerfile b/Dockerfile
index 82e340b..da9e871 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -8,6 +8,6 @@ ARG VERSION=2.30.3
 # install Prometheus
 RUN curl -L https://github.com/prometheus/prometheus/releases/download/v${VERSION}/prometheus-${VERSION}.linux-amd64.tar.gz | tar zxvf - --strip-components 1
 
-COPY start.sh /app/pkg/
+COPY docker /
 
 CMD [ "/app/pkg/start.sh" ]
diff --git a/docker/app/code/default_prometheus_variables.sh b/docker/app/code/default_prometheus_variables.sh
new file mode 100755
index 0000000..b479aee
--- /dev/null
+++ b/docker/app/code/default_prometheus_variables.sh
@@ -0,0 +1,4 @@
+#!/bin/bash
+
+# https://prometheus.io/docs/prometheus/latest/storage/#operational-aspects
+export retention_time="15d"
diff --git a/start.sh b/docker/app/pkg/start.sh
similarity index 50%
rename from start.sh
rename to docker/app/pkg/start.sh
index f269987..7a68d4b 100755
--- a/start.sh
+++ b/docker/app/pkg/start.sh
@@ -11,5 +11,14 @@ fi
 
 chown -R cloudron:cloudron /app/data
 
+if [ ! -f /app/data/prometheus_variables.sh ]; then
+    echo "=> Copy default prometheus variable file since it does not exist"
+    cp /app/code/default_prometheus_variables.sh /app/data/prometheus_variables.sh
+fi
+
+echo "=> Source custom variables"
+source /app/data/prometheus_variables.sh
+
 echo "=> Starting Prometheus"
-exec /usr/local/bin/gosu cloudron:cloudron /app/code/prometheus --config.file=/app/data/config/prometheus.yml --storage.tsdb.path=/app/data/runtime
+echo "=> Starting with retention time of $retention_time"
+exec /usr/local/bin/gosu cloudron:cloudron /app/code/prometheus --config.file=/app/data/config/prometheus.yml --storage.tsdb.path=/app/data/runtime --storage.tsdb.retention.time="${retention_time:-15d}"
diff --git a/test/package-lock.json b/test/package-lock.json
index 0252d01..104d531 100644
--- a/test/package-lock.json
+++ b/test/package-lock.json
@@ -33,9 +33,9 @@
       "integrity": "sha512-8UT/J+xqCYfn3fKtOznAibsHpiuDshCb0fwgWxRazTT19Igp9ovoXMPhXyLD6m3CKQGTMHgqoxaFfMWaL40Rnw=="
     },
     "@types/node": {
-      "version": "16.10.1",
-      "resolved": "https://registry.npmjs.org/@types/node/-/node-16.10.1.tgz",
-      "integrity": "sha512-4/Z9DMPKFexZj/Gn3LylFgamNKHm4K3QDi0gz9B26Uk0c8izYf97B5fxfpspMNkWlFupblKM/nV8+NA9Ffvr+w==",
+      "version": "16.10.3",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-16.10.3.tgz",
+      "integrity": "sha512-ho3Ruq+fFnBrZhUYI46n/bV2GjwzSkwuT4dTf0GkuNFmnb8nq4ny2z9JEVemFi6bdEJanHLlYfy9c6FN9B9McQ==",
       "optional": true
     },
     "@types/yauzl": {
@@ -617,9 +617,9 @@
       "dev": true
     },
     "is-glob": {
-      "version": "4.0.2",
-      "resolved": "https://registry.npmjs.org/is-glob/-/is-glob-4.0.2.tgz",
-      "integrity": "sha512-ZZTOjRcDjuAAAv2cTBQP/lL59ZTArx77+7UzHdWW/XB1mrfp7DEaVpKmZ0XIzx+M7AxfhKcqV+nMetUQmFifwg==",
+      "version": "4.0.3",
+      "resolved": "https://registry.npmjs.org/is-glob/-/is-glob-4.0.3.tgz",
+      "integrity": "sha512-xelSayHH36ZgE7ZWhli7pW34hNbNl8Ojv5KVmkJD4hBdD3th8Tfk9vYasLM+mXWOZhFkgZfxhLSnrwRr4elSSg==",
       "requires": {
         "is-extglob": "^2.1.1"
       }