add fundamentals of backend engineering and protocols

README.md

@@ -1,18 +1,71 @@
-## ☁️🧰 master orchestration && backend engineering 
+## ☁️🧰 master orchestration and backend engineering 
 
 
 <br>
 
-### fundamentals
+### learn the fundamentals
 
 <br>
 
 * **[communication](communication/)**
+  * Request Response model
+  * Synchronous vs. Asynchronous workloads
+  * Push
+  * Polling and Long Polling
+  * Server Sent Events
+  * Publish Subscribe (Pub/Sub)
+  * Multiplexing vs. Demultiplexing
+  * Stateful vs. Stateless
+  * Sidecar Pattern
+
+<br>
+
 * **[protocols](protocols/)**
+  * protocol properties
+  * protocol properties
+  * OSI model
+  * internet protocol
+  * UDP
+  * TCP
+  * TLS
+  * HTTP/1.1
+  * WebSockets
+  * HTTP/2
+  * HTTP/3
+  * gRPC
+  * WebRTC
+
+  <br>
+
 * **[HTTP](https/)**
+  * https communication 
+  * https over TCP with TLS 1.2
+  * https over TCP with TLS 1.3
+  * https over QUIC (HTTP/3)
+  * https over TFO with TLS 1.3
+  * https over TCP with TLS 1.3 and ORTT
+  * https over QUICK with ORTT
+
+  <br>
+
 * **[execution](execution/)**
-* **[proxy](proxy)**
-* **[load balance](load_balance)**
+  * backend execution patterns
+  * the process, the thread, the cpu time
+  * reading and sending socket data
+  * the listener, the acceptor, the reader
+  * single listener, acceptor, and reader thread execution pattern
+  * single listener, acceptor, and multiple readers thread execution pattern
+  * single listener, acceptor, reader with message load balancing execution pattern
+  * multiple accepter threads on a single socket execution pattern
+  * multiple listeners, acceptors, and reader with socket sharding execution pattern
+  * backend idempotency
+  * nagle's algorithm
+
+  <br>
+
+* **[proxy and load balance](proxy_and_lb)**
+  * proxy vs. reverse proxy
+  * Layer 4 vs. Layer 7 load balancers
 
 
 <br>

communication/README.md

@@ -0,0 +1,179 @@
+## 📡 communication design patterns
+
+<br>
+
+### Request Response model
+
+<br>
+
+#### used in
+
+    - the web, HTTP, DNS, SSH
+    - RPC (remote procedure call)
+    - SQL and database protocols
+    - APIs (REST/SOAP/GraphQL)
+
+<br>
+
+
+#### the basic idea
+
+    1. clients sends a request
+        - the request structure is defined by both client and server and has a boundary.
+    2. server parses the request
+        - the parsing cost is not cheap (e.g. `json` vs. `xml` vs. protocol buffers)
+        - for example, for a large image, chunks can be sent, with a request per chunk
+    3. Server processes the request
+    4. Server sends a response
+    5. Client parse the Response and consume
+
+<br>
+
+#### an example in your terminal
+
+
+* see how it always get the headers firsts:
+
+```bash
+curl -v --trace marinasouza.xyz
+
+== Info:   Trying 76.76.21.21:80...
+== Info: Connected to marinasouza.xyz (76.76.21.21) port 80 (#0)
+=> Send header, 79 bytes (0x4f)
+0000: 47 45 54 20 2f 20 48 54 54 50 2f 31 2e 31 0d 0a GET / HTTP/1.1..
+0010: 48 6f 73 74 3a 20 6d 61 72 69 6e 61 73 6f 75 7a Host: marinasouz
+0020: 61 2e 78 79 7a 0d 0a 55 73 65 72 2d 41 67 65 6e a.xyz..User-Agen
+0030: 74 3a 20 63 75 72 6c 2f 37 2e 38 38 2e 31 0d 0a t: curl/7.88.1..
+0040: 41 63 63 65 70 74 3a 20 2a 2f 2a 0d 0a 0d 0a    Accept: */*....
+== Info: HTTP 1.0, assume close after body
+<= Recv header, 33 bytes (0x21)
+0000: 48 54 54 50 2f 31 2e 30 20 33 30 38 20 50 65 72 HTTP/1.0 308 Per
+0010: 6d 61 6e 65 6e 74 20 52 65 64 69 72 65 63 74 0d manent Redirect.
+0020: 0a                                              .
+<= Recv header, 26 bytes (0x1a)
+0000: 43 6f 6e 74 65 6e 74 2d 54 79 70 65 3a 20 74 65 Content-Type: te
+0010: 78 74 2f 70 6c 61 69 6e 0d 0a                   xt/plain..
+<= Recv header, 36 bytes (0x24)
+0000: 4c 6f 63 61 74 69 6f 6e 3a 20 68 74 74 70 73 3a Location: https:
+0010: 2f 2f 6d 61 72 69 6e 61 73 6f 75 7a 61 2e 78 79 //marinasouza.xy
+0020: 7a 2f 0d 0a                                     z/..
+<= Recv header, 41 bytes (0x29)
+0000: 52 65 66 72 65 73 68 3a 20 30 3b 75 72 6c 3d 68 Refresh: 0;url=h
+0010: 74 74 70 73 3a 2f 2f 6d 61 72 69 6e 61 73 6f 75 ttps://marinasou
+0020: 7a 61 2e 78 79 7a 2f 0d 0a                      za.xyz/..
+<= Recv header, 16 bytes (0x10)
+0000: 73 65 72 76 65 72 3a 20 56 65 72 63 65 6c 0d 0a server: Vercel..
+<= Recv header, 2 bytes (0x2)
+0000: 0d 0a                                           ..
+<= Recv data, 14 bytes (0xe)
+0000: 52 65 64 69 72 65 63 74 69 
+```
+
+
+<br>
+
+----
+
+### Synchronous vs. Asynchronous workloads
+
+<br>
+
+#### Synchronous I/O: the basic idea
+
+    1. Caller sends a request and blocks
+    2. Caller cannot execute any code meanwhile
+    3. Receiver responds, Caller unblocks
+    4. Caller and Receiver are in sync
+
+
+<br>
+
+##### example (note the waste!)
+
+    1. program asks OS to read from disk
+    2. program main threads is taken off the CPU
+    3. read is complete and program resume execution (costly)
+
+<br>
+
+#### Asynchronous I/O: the basic idea
+
+    1. caller sends a request
+    2. caller can work until it gets a response
+    3. caller either:
+        - checks whether the response is ready (epoll)
+        - receiver calls back when it's done (io_uring)
+        - spins up a new thread that blocks
+    4. caller and receiver not in sync
+
+<br>
+
+#### Sync vs. Async in a Request Response
+
+    - synchronicity is a client property
+    - most modern client libraries are async
+
+
+<br>
+
+#### Async workload is everywhere
+    - async programming (promises, futures)
+    - async backend processing
+
+<br>
+
+----
+
+### Push
+
+
+<br>
+
+----
+
+### Polling
+
+
+<br>
+
+---
+
+### Long Polling
+
+
+<br>
+
+---
+
+### Server Sent Events
+
+
+<br>
+
+----
+
+### Publish Subscribe (Pub/Sub)
+
+
+<br>
+
+---
+
+### Multiplexing vs. Demultiplexing
+
+
+<br>
+
+---
+
+### Stateful vs. Stateless
+
+
+<br>
+
+---
+
+### Sidecar Pattern
+
+
+<br>