https://pdf.yozocloud.cn/index.html#/Pdf2word : Evermore PDF toolkit offers free, high-quality PDF conversion and processing services
https://www.cnblogs.com/cjsblog/p/9439331.html ：Elasticsearch
https://www.cnblogs.com/cjsblog/p/9459781.html：Logstash
https://www.cnblogs.com/cjsblog/p/9445792.html：Filebeat
https://cloud.tencent.com/developer/article/1451728 : stand-alone build hadoop + hive + spark environment
https://www.cnblogs.com/mrlinfeng/p/6146866.html : Nginx reverse proxy, load balancing, redis session sharing, keepalived availability
https://www.cnblogs.com/mrlinfeng/p/6341225.html : Keepalived + LVS build a high-availability load balancing