Design patterns

Protocols

https://developer.mozilla.org/en-US/docs/Web/HTTP/Overview
- […] the browser is always the entity initiating the request. It is never the server (though some mechanisms have been added over the years to simulate server-initiated messages).
- in order to mitigate this flaw (each http request requiring a new TCP connection), HTTP/1.1 introduced pipelining (which proved difficult to implement) and persistent connections: the underlying TCP connection can be partially controlled using the Connection header. HTTP/2 went a step further by multiplexing messages over a single connection, helping keep the connection warm and more efficient.
https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST (How POST works)
https://fasterthanli.me/articles/the-http-crash-course-nobody-asked-for once I was asked in a interview how can you transfer a file over http, here is the explanation of chuncked transfer-enconding from that link: You don’t yet know how large it’s going to be. So you can’t send a Content-Length header. What do?
```
You send chunks! Like so:

POST / HTTP/1.1
Host: example.org
Connection: close
Transfer-Encoding: chunked

4
Help
C
I am chunked
0
```

Every chunk is prefixed by L\r\n, where L is the length of the next chunk, formatted as hexadecimal ("I am chunked" is 12 bytes long, hence, 0xC).
```

State Transfer: for example the master sends to all workers its RAM state
Replicated State Machine: Send external inputs (e.g. set x = 1), in other words: operations