Actually wait let's reorder those args

Hopefully really this time

Dockerfile

@@ -3,6 +3,11 @@ ARG MINECRAFT_VERSION="1.16.5"
 ARG FORGE_VERSION="36.2.26"
 ARG JRE_VERSION="openjdk8-jre"
 
+ARG UID=1520
+ARG USER=minecraft
+ARG GID=1520
+ARG GROUP=minecraft
+
 # The first stage just builds up the modpack
 FROM alpine:latest AS build
 
@@ -26,10 +31,18 @@ FROM alpine:latest AS final
 
 # Use only a subset of arguments
 ARG JRE_VERSION
+ARG UID
+ARG USER
+ARG GID
+ARG GROUP
 
 # Build the thing up
 RUN apk add bash curl findutils rsync screen "${JRE_VERSION}"
 WORKDIR /minecraft
 COPY --from=build /minecraft .
+RUN addgroup -g "${GID}" "${GROUP}" && \
+	adduser -h /minecraft -s /bin/sh -D -H -u "${UID}" -G "${GROUP}" "${USER}" && \
+	chown "${USER}:${GROUP}" /minecraft
+USER $USER
 CMD [ "bash", "start-server.sh" ]
 EXPOSE 25565

start-server.sh

@@ -22,7 +22,7 @@ if [ -n "$FORGE_PACK_ZIP" ]; then
 		echo "Found modpack directory: $directory"
 	fi
 	echo "Syncing content to /minecraft"
-	rsync --ignore-existing "$directory"/ /minecraft/
+	rsync --no-perms --no-owner --no-group --ignore-existing "$directory"/ /minecraft/
 	popd > /dev/null 2>&1
 fi