Elasticsearch/Solr/ELK Stash
Caveat of using Elasticsearch as datastore: https://www.elastic.co/blog/found-elasticsearch-as-nosql
Sync Elasticsearch with MySQL: https://towardsdatascience.com/how-to-synchronize-elasticsearch-with-mysql-ed32fc57b339
Solr vs ELK
https://kknews.cc/zh-tw/tech/r9y4z5o.html
Elastic Search
https://godleon.github.io/blog/Elasticsearch/Elasticsearch-getting-started/

Solr vs. Elasticsearch誰是開源搜尋引擎王者

https://sematext.com/blog/solr-vs-elasticsearch-differences/
Solr
static data
Faceting, grouping (collapsing), powerful filtering, etc
Depends on Apache Zookeeper
Managed-schema file

Elasticsearch
Near Real-Time search
More dynamic. data can easily move around the cluster as its nodes come and go, and this can impact stability and performance of the cluster.
Zen - built-in ZooKeeper-like component
Schemaless