# SOLACE PubSub+

###### tags: `learning`

## Introduction
- 整合跨廠、Data center、Cloud Server及IoT，作為設備之間即時通訊的管理平台
1. Event Management
- 支援EDA (Event-Driven Architecture)
- 偵測特定Event
2. Event Streaming
- 建立Event mesh以共享數據
- Event Mesh是一個由事件代理系統(Event Broker)所組成的網路架構層，可以將某應用程式產生的event動態route到其他應用程式(無論他部屬在哪裡)
- Event Broker
- 接收從Producers產生的事件訊息，並將事件訊息route給事件訂閱者(Consumers)
- Event Broker可以部屬在
1. Cloud (包含公有雲&私有雲,etc)
2. Software (各類Container或虛擬機管理平台)
3. Appliance
- 名詞解釋

3. Monitor System health & performance

- "+" 表示支援除了Publish/Subscribe之外的訊息交換模式
1. Request/Reply (Send/Receive)
- 兩個P2P通道
3. P2P
4. Streaming
5. Caching & Replay

## [Topic](https://docs.solace.com/Messaging/Topic-Architecture-Best-Practices.htm#topic-bp-definitions)
- 可以想成一個規則，可以定義接收哪些producer的哪些event message
$\Rightarrow$ topic是consumer(subscriber)的訂閱單位
- 分成publish topics及subscribe topics
- [SMF(Solace Message Format)](https://docs.solace.com/Messaging/SMF-Topics.htm)
- Syntax: `a/b/c/.../n` (用LEVEL分類)
- eg. `animals/domestic/cats`
- Case-Sensitive
- 萬用字元(for subscribe topic): `*`, `>`: 放在最後一個LEVEL, `!`: except
- eg. `animals/*/cats/>` matches the topics `animals/domestic/cats/persian`& `animals/wild/cats/leopard`

## Message Deliver Mode:
1. Direct Message
- Client直接訂閱Topic
- Client必須connect event broker才收的到訊息(訊息不會保留)
- 通道壅塞時容易掉包
3. Garanteed Message
- Event Broker會向producer acknowledge收到的訊息 (by acknowledge receipt)
- Event Broker會將收到的訊息保存在一個Message storage (一個event broker的endpoint)
- Event Broker會確保Client收到訊息, 並在收到acknowledge receipt之後將它從Message storage刪除
- Endpoint types
1. Queues: Queues can subscribe to more than one topic and receive messages for all topics matching their subscriptions.
2. Topic Endpoints: A topic endpoint attracts messages published to a single topic for which the topic endpoint has a matching subscription.

## Message VPN
- 在Event Broker上，用來grouping
- 哪些client可以接收哪些publisher publish的messages，他們connect到同一個Message VPN
- 一個VPN中的publisher送出的訊息只會送給連接到同樣VPN的consumer

- 一個Message VPN中包含一或多個topic (不確定概念是否正確?
- VPN是一個channel
- topic是一個實體訂閱單位

## Event Mesh DMR