Elasticsearch的入門非常簡單易學。
由於有豐富的原生的Restful API,創建索引，上傳數據，搜索都可以在很短時間內學會使用。官網上也有很多語言的client API與ES集群交互，有豐富的插件比如head,marvel等等。
那如果用ES這個開源項目做SAAS（software as a service)，比如搜索服務，是否可以直接用它原生的API呢？
jest是一款java Rest client，它支持SSL、proxy等等，而原生的transport client是TCP連接，用戶認證授權要自己想辦法實現，並且封裝接口控制用戶的操作。
從jest的文檔中我找到了一部分答案：
ElasticSearch does not have Java rest client. It has only native client comes built in. That is the gap. You can add security layer to HTTP but native API. That is why none of SAAS offerings can be used with native api. -- Searchly
原生的API沒有任何安全保護層，而對於HTTP來說加一層安全認證是比較簡單的。
jest client和原生的client的比較還有：
So if you have several ES clusters running different versions, then using the native (or transport) client will be a problem, and you will need to go HTTP (and Jest is the main option I think). If versioning is not an issue, the native client will be your best option as it is cluster aware (thus knows how to route your queries and does not need another hop), and also moves some computation away from your ES cluster (like merging search results that will be done locally instead of on the data node). -- Rotem Hermon
如果ES集群的版本不同，用HTTP client會好些。如果版本不是問題，原生的client是最好的選擇。因為它是culster-aware的，並且可以從ES集群分擔一部分計算，比如合並搜索結果是在本地client執行的而不是data node。
There are several alternative clients available when working with ElasticSearch from Java, like Jest that provides a POJO marshalling mechanism on indexing and for the search results. In this example we are using the Client that is included in ElasticSearch. By default the client doesn't use the REST API but connects to the cluster as a normal node that just doesn't store any data. It knows about the state of the cluster and can route requests to the correct node but supposedly consumes more memory. For our application this doesn't make a huge difference but for production systems that's something to think about. -- Florian Hopf
原生的client像一個單純的節點連接集群，它知道集群的狀態和路由請求，這樣會消耗多一些內存，在生產環境是值得考慮的影響。
開源的東西到底要不要經常用呢？感覺初級開發人員還是少用為好。