diff --git a/docker/Dockerfile b/docker/Dockerfile
index 1e45586..ea8f1de 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -1,9 +1,13 @@
 FROM ubuntu:latest
 
+ENV PORT "8388"
+ENV METHOD "aes-256-cfb"
+ENV KEY "changeme"
+
+EXPOSE "$PORT"
+
+CMD ssserver -p "$PORT" -m "$METHOD" -k "$KEY"
+
 RUN apt-get update
 RUN apt-get install -y python-pip
 RUN pip install shadowsocks
-
-EXPOSE 8388
-
-CMD ssserver -p 8388 -m "aes-256-cfb" -k "$KEY"