added Dockerfiles

examples/frontend/Dockerfile

@@ -1,10 +1,20 @@
+FROM node:8.16.0-alpine AS build
+
+ADD ./frontend /app
+WORKDIR /app
+
+# install frontend
+RUN npm install -g yarn && yarn install
+
+RUN npm run build:prod
+
 FROM alpine:latest
 
 # 安装nginx
 RUN mkdir /run/nginx && apk add nginx
 
 # 拷贝编译文件
-COPY dist  /app/dist
+COPY --from=build /app/dist /app/dist
 
 # 拷贝nginx代理文件
 COPY crawlab.conf /etc/nginx/conf.d