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4a1s/ASCN/T - Aula 2.md

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+🌫 18 Setembro 2023 - #ASCN
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+- ## Why distributed systems?
+- Modularity, decoupling different concerns.
+- Performance.
+- Dependability
+- ## How to distribute?
+- ### 1. Monolythic system
+- Architecture: [[Monolithic system.excalidraw]]
+- Multiple services for multiple targets in the same server
+- ## 2. Distributed systems
+  id:: 65120d55-6bed-47db-bd53-cc4f627c33dc
+- Main distribution concerns:
+  1. Replication
+  2. Partitioning
+  3. Service-orientation
+- All of these address scaling out a service/application.
+- Not mutually exclusive, can be combined.
+- ### 2.1 Replication
+- Architecture: [[Replication.excalidraw]]
+- Multiple copies  of the same data and functionality
+- Addresses resilience and scale-out
+- ### 2.2 Partitioning
+- Architecture: [[Partitioning.excalidraw]]
+- A server is split horizontally (Sharding).
+- Addresses scale-out.
+- Can be applied to computation, data, ...
+- ### 2.3 SOA - Service-Oriented Architecture
+- Architecture: [[SOA.excalidraw]]
+- Addresses scale-out and modularity.
+- Example: micro-services.
+- #### 2.3.1 Microservices
+- Each service implements specific functionality.
+- Services can scale independently.
+- Decomposition may be troublesome: how micro is micro?
+- Consistency.
+- Complex deployment and testing
+- ## Distributed architectures
+- ### 1. Client-server
+- Architecture: [[client-server.excalidraw]]
+- Functionality and data are in the server.
+- A stub runs embedded in the client.
+- The stub is part of the server software package
+	- E.g., the Web (“protocol” is HTTP)
+- ### 2. Proxy Server
+- Architecture: [[proxy.excalidraw]]
+- Multiple servers can be used transparently.
+- The proxy is a performance and availability bottleneck.
+	- E.g. MongoDB
+- ### 3. Master Server
+- Architecture: [[master.excalidraw]]
+- Scale out!
+	- E.g. HDFS
+- ### 4. Server Group
+- Architecture: [[server-group.excalidraw]]
+- All servers can process requests.
+- Coordination may be necessary.
+- Resiliency!
+	- E.g. ZooKeeper
+- ### 5. Bus
+- Architecture: [[bus.excalidraw]]
+- The bus routes messages.
+- Participants publish and consume messages to/from the bus.
+- Decouples producers from consumers.
+- **Flexibility!**
+	- E.g. Kafka
+- ### 6. Multi-tier
+- Architecture: [[multi-tier.excalidraw]]
+- Each server acts as a client of the next tier.
+- Allows independent deployment and scaling of different functionality.
+- E.g. AS + DBMS:
+	- “protocol A” == Web (e.g.)
+	- “Stub B” == Database Driver!
+	- “protocol B” uses SQL
+- #### 6.1 State in multi-tier
+- Persistent state is harder to replicate and shard.
+- Computation is easier to replicate and shard.
+- No state in upper tiers:
+	- Web browser
+- Transient / cached state in middle tiers:
+	- Application server
+- Persistent state at lower tiers:
+	- Database