System Theory

• https://en.wikipedia.org/wiki/Client%E2%80%93server_model
• A distributed application architecture model
• usually used to describe a networked service where multiple Clients communicate with a single Server
• The term 'work' is used to describe the inputs and outputs of such a model. The 'work' performed is strictly scoped.
  • For example, consider the architecture for an MMO video game. The client-server model applies to the design of Players (Clients) connecting to a match, which is hosted on the game server (Server). The 'work' performed here may include updates to a Player's in-game position based on control input, chat messages, connection status, etc.
  • In addition to communicating with the game server, Players may establish direct connection to other Players in their match in a client-to-client or decentralized manner, where 'work' is shared and managed between the Clients themselves, under authority of the Server. This is where terminology begins to miss the point, as these features share a likeness to p2p networking.

• Peer-to-peer - Wikipedia

Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the application. They are said to form a peer-to-peer network of nodes.

Peers make a portion of their resources, such as processing power, disk storage or network bandwidth, directly available to other network participants, without the need for central coordination by servers or stable hosts. Peers are both suppliers and consumers of resources, in contrast to the traditional client–server model in which the consumption and supply of resources is divided.

• UDP and TCP share the same space in a network stack and operate on top of the IP protocol.

• UDP has no built-in notion of State, TCP does. However, stateless protocols can be built on lower-level stateful ones.. and vice-versa. It's just a matter of abstraction.

  • for example HTTP is a stateless protocol, built

  on TCP (stateful), which is built on IP (stateless)

• TCP provides connection guarantees that a client receives packets IN ORDER and exactly in the condition they were sent (thanks to checksums in headers), at the cost of some performance (to ensure packet sequencing, checking headers, establishing connection, etc)
  • UDP does NOT provide connection guarantees.
    • UDP does have checksums though, and thus ensures packets are received in same condition that they were sent.
  • Packets can be sent and lost, it doesn't intrinsically matter in UDP that the client didn't receive them.
  • The loss of built-in guarantees does come with a performance boost though, as well as a network protocol that is quite flexible in its simplicity.

The Portable Operating System Interface

Domain-driven design

• focuse on modeling software to match a domain according to input from domain experts.
• against the idea of a single unified model
  • divides large system into bounded contexts, each with their own model

• Test-driven development

Content Management Frameworks