diff --git a/distillery/lib/30_slug.sh b/distillery/lib/30_slug.sh
index 31bb1fe..8c6341d 100644
--- a/distillery/lib/30_slug.sh
+++ b/distillery/lib/30_slug.sh
@@ -43,6 +43,16 @@ function compute_instance_domain() {
 }
 INSTANCE_DOMAIN="$(compute_instance_domain "$SLUG")"
 
+# compute the url pointing to an instance
+function compute_instance_url() {
+    if [ -n "$CERTBOT_EMAIL" ]; then
+        echo -n "https://"
+    else
+        echo "http://"
+    fi
+    compute_instance_domain "$@"
+}
+
 # Next we need a username base. 
 # This will be used as a username across the system (linux), MySQL and GraphDB. 
 # For this we can only allow [0-9a-zA-Z-], hence we have to escape. 
diff --git a/distillery/update_prefix_config.sh b/distillery/update_prefix_config.sh
index 20f059b..f73da21 100644
--- a/distillery/update_prefix_config.sh
+++ b/distillery/update_prefix_config.sh
@@ -15,7 +15,7 @@ date | tee -a "$DEPLOY_PREFIX_CONFIG"
 
 # update all the instances
 for slug in $(sql_bookkeep_list); do
-    INSTANCE_DOMAIN="http://$(compute_instance_domain "$slug")"
+    INSTANCE_DOMAIN="$(compute_instance_url "$slug")"
     echo "$INSTANCE_DOMAIN:" | tee -a "$DEPLOY_PREFIX_CONFIG"
     
     read -r INSTANCE_BASE_DIR MYSQL_DATABASE MYSQL_USER GRAPHDB_REPO GRAPHDB_USER GRAPHDB_PASSWORD <<< "$(sql_bookkeep_load "${slug}" "filesystem_base,sql_database,sql_user,graphdb_repository,graphdb_user,graphdb_password" | tail -n +2)"