Hybris支持cluster mode的部署，不同節點間通過局域網使用UDP進行通信。

而SAP Netweaver經典的3層layer里就提到Application layer也支持multiple node:

比如在AG3用tcode SM53查看，發現其是由3個node組成：

Cache invalidation
無論Hybris，還是Netweaver，都面臨一個需要解決的問題，即cache / buffer invalidation.

Cache Invalidation Concept in Hybris

The core of a Hybris Cluster is a network communication system that makes sure the cache of each individual cluster member only holds valid data. The nodes in the Hybris Cluster communicate using TCP (JGroups) or UDP, by sending signals to other nodes that mark some cache entries as invalid because a database item has been changed. The following is the overview of the cache invalidation process:

(1) A description of a product has changed. Therefore, all cache entries referring to the product are invalid.
(2) A cluster node where the modification has been done sends a notification to all cluster nodes that all cache entries holding the product are invalid.
(3) Nodes that hold the product in their cache discard the cached data of the product and re-retrieve the product from the database the next time the product is used.

node之間用于通知cache invalidation的協議有UDP Multicast, UDP Unicast, or JGroups.各有優缺點：
(1) JGroups provides the fastest communication and can be used both in the cloud for testing purposes and in a LAN or WAN network.
(2) UDP Multicast has some limitations in that some routers do not allow multicast network traffic by default. Amazon Elastic Compute Cloud (Amazon EC2) does not work using UDP, either.

Cache Invalidation Concept in Netweaver

SAP help上分了13個步驟詳細講解：

by default cluster mode is deactivated. See startup log:

cloud foundry也支持分布式部署，節點之間通過消息通信。通過組件NATS實現

在安裝時也能觀察到：

NATS是CF啟動時需要執行的5個process之一：

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