Note: Before starting reading this chapter, let us be clear about below things:
1. System design is a very vast topic, and covering every aspect is impossible.
2. This chapter should be treated as a “getting started” or “introduction” to system design. We go through most of the concepts, but in brief.
3. I have written detailed chapter for some complex topics.
1.1 Before designing a system, below are the topics that we should be considering before designing any system.
1.1.2. Define API’s
1.1.7. Class Diagram
1.1.8. Security and Privacy
1.1.9. Cost effective
We shall discuss about the above topics in brief.
Before designing a system, be clear about the features of the system. If you are appearing for an interview, ask the features to be included to the interviewer.
If you are to develop a chat application, you need to ask if there is only one to one chat or group chat. The level of security required and other features required.
1.1.2 Define API’s
Once we define the features, we need to come up with the API’s. How many API’s are needed, when to call those API’s and who will call the APIs.
Once we decide upon the API, we need to decide about the availability of the system. Particularly we need to decide upon how available the service should be.
For example: If a service goes down or a data center goes down, what should be the state of the system.
We need to decide upon how fast the system should be. If it is a chat application, the system should be very fast and responsive. Then we need to improve the latency of the system.
One way to improve the latency is by using cache system, CDN.
If it is a mail system, then it can be less responsive than our chat application.
Once we decide on latency, we need to think about the scalability of the system. Especially on how the system will behave when there are 100 users, or 1000 users, or 1M users.
Now we should think about how durable the system should be. If the system you are designing is a code backup repository service, then the system should be highly durable and the associated security features needed for that data needs to be taken care.
1.1.7 Class Diagram
If you are needed to design a parking lot or an elevator system, you need to design the class and how multiple classes interact with each other.
Here the interviewer will be interested in OOP concepts and how effectively you use OOP concepts.
1.1.8 Security and Privacy
This is important when we are designing an authentication or credit card storage system.
1.1.9 Cost effective
Once we decide upon all the above features, we need to think how cost effective the system will be. Is there any alternative system available that are more cost effective?
1.2 Below are the topics to be known before designing a system
1.2.1. Vertical and Horizontal Scaling
1.2.2. CAP Theorem
1.2.3. ACID and BASE properties
1.2.4. Partitioning or Sharding data
1.2.5. consistent hashing
1.2.6. Strong vs Eventual Consistency
1.2.7. Optimistic vs pessimist locking
1.2.8. Relational vs No SQL DB
1.2.10. Datacenters / Racks/ Hosts
1.2.11. CPU/Memory/Network Bandwidth
1.2.12. Random vs sequential read/write on disks
1.2.13. http vs http2 vs web sockets
1.2.14. TCP/IP Model
1.2.15. IPv4 vs IPv6
1.2.16. TCP vs UDP
1.2.17. DNS lookup
1.2.18. HTTPS vs TLS
1.2.19. Certificate Authority
1.2.20. Load Balancers
1.2.22. Design Pattern and Object Oriented design
1.2.23. Virtual Machines and containers
1.2.25. Map reduce
1.2.26. Multithreading, Concurrency, locks, Synchronization.
1.2.1 Vertical and Horizontal Scaling
If we want to serve more users, then we need to scale our system. We can do it in 2 ways.
1. Vertical Scaling
2. Horizontal Scaling.
1. Vertical Scaling: It refers to adding more memory, RAM, increase the processor speed all in a single host or a computer.
2. Horizontal Scaling: It refers to adding more hosts or computers as the number of users increases.
1.2.2 CAP Theorem
CAP: Consistency, Availability and Partition Tolerance.
Consistency: It refers to the read is the most recent write.
Availability: It refers to, when user asks for a request, the system should be available to respond.
Partition Tolerance: The system should be able to function even if any one node or part of the system fails.
CAP theorem says that it is only possible to achieve any 2 out of 3 things.
1.2.3 ACID and BASE properties
ACID: Atomicity Consistency Isolation Durability
BASE: Basically Available Soft-state Event
ACID is for relational database.
BASE is for No-SQL DB.
1.2.4 Partitioning or Sharding data
If we have huge amount of data, it is not possible to store all the data in a single DB system. Hence we need to store them in a different systems(nodes). Hence now Sharding of data comes to play. We need to choose to partition the data such that every node of DB is responsible for some of the data of that large amount of data
1.2.5 consistent hashing
Consistent hashing is a way of organizing the key value pair for distributed data. So that when we want to scale the system, data changes due to additional keys will be minimum.
1.2.6 Strong vs Eventual Consistency
Strong consistency refers to the read will have the latest write.
Eventual consistency refers that the read will have some write, but eventually will have the latest write.
Strong consistency is used in relational DB.
No SQL DB can be configured with Strong or Eventual Consistency.
1.2.7 Optimistic vs pessimist locking
In optimist locking, before committing any transaction we check and see if no other system is using the resource.
In pessimist locking, we acquire lock before committing any transaction.
1.2.8 Relational vs No SQL DB
Relational DB will provide ACID properties, but No SQL DB provides high availability and is highly scalable.
Hence Depending on the system, we check and use which fits better.
Caching is frequently used in web-browser, it will store most frequently used data such as css files. Hence when you visit the website, it can be accessed quickly.
1.2.10 Datacenters / Racks/ Hosts
Server: A server is a computer, that is used to serve the requests. Most of the time, a server will serve only one type of request. There are different types of servers like Web server, Proxy server, mail server.
Racks: Racks is a collection of servers.
Datacenter: A datacenter is a collection of multiple networking components like servers, routers, switches, firewalls inside a building. Datacenter can be a dedicated building or inside a room. To support these multiple servers and other networking components, they need to be kept cool, hence they need into kept in a AC room.
Cluster: It is a collection of datacenter.
Hosts: A host is a computer device; it is used to communicate to another hosts on the network.
1.2.11 CPU/Memory/Network Bandwidth
As all the above resources are costly and are limited, they should be effectively utilized. Many big companies, design their own datacenter to further reduce energy costs.
1.2.12 Random vs sequential read/write on disks
Sequential read and write are always faster than random read and writes on the disk.
1.2.13 http vs http2 vs web sockets
http: It is a request, reply architecture between client and server.
http2: It can do multiple requests over a single connection
web-sockets: It is fully bidirectional communication between client and server.
10.2.14 TCP/IP Model
TCP/IP model is used for communicating between different computers or applications over the internet. Any device that is connected to open internet should agree to TCP/IP model.
It has 4 layers:
Layer 4: Application Layer
Layer 3: Transport Layer
Layer 2: Internet Layer
Layer 1: Link Layer
All the 4 layers performs different functions.
10.2.15 IPv4 vs IPv6
Internet Protocol addressing is a way that 2 computers communicate with each other over the internet. Each device that is connected to internet will have an IP address attached to it.
IPv4: Internet Protocol version 4. It has 2^32 ip address in total.
IPv6: Internet Protocol version 6, as IPv4 address is running out, the technology is moving towards IPv6. It has 2^128 address.
10.2.16 TCP vs UDP
These 2 protocols are used to transfer packets over the internet.
TCP: It stands for Transmission Control Protocol. It is connection oriented protocol. It guarantees delivery of the packet to the required recipient. Retransmission of lost packets can be done in TCP.
UDP: It stands for User Datagram Protocol. It is a connection less protocol. The packet reaching to the destination cannot be guaranteed. It is faster than TCP.
10.2.17 DNS lookup
Domain Name Lookup service. When you type “prodevelopertutorial.com”, then the request goes to DNS which does the translation of the address into an IP address.
10.2.18 HTTPS vs TLS
TLS stands for Transport Layer Security, used to secure communication between client and server.
When TLS is used with HTTP, it will become HTTPS.
10.2.19 Certificate Authority
A certificate authority is an entity that issues digital certificates. A CA is tasked with identifying the website and ensuring safe data transfer between website and its clients.
10.2.20 Load Balancers
Once our application gets more number of visitors, we need to include more application servers to serve those customers. So we place those application servers behind a load-balancer. A load balancer is a server that will be the first point of contact of user request, based on some model it will distribute those requests evenly among the available application server such that no server is overloaded.
Load balancer server will also provide security for DDOS attacks, as those attacks will hit load balancer and application servers will be safe.
CDN stands for content delivery network. It will help to improve the performance and latency by keeping the requested data near to the user.
For example, if you are seeing a YouTube video, if that video is near you, it will stream faster. This is done with the help of CDN.
10.2.22 Design Pattern and Object Oriented design
When developing [coding] a system, it is important to follow coding standards. Design pattern will give an implementation idea for commonly occurring problems. Some of the design pattern to know are:
1. Singleton Design Pattern: Here only one instance of the class will be available.
2. Adapter Design Pattern: Here two incompatible elements can transfer data with adapter design pattern.
3. Proxy Design Pattern: It is used in place of another component that can be delivered later.
4. Factory Design Pattern: The concept is to create an object without exposing logic to the client.
Most of the system today will follow Object Oriented Design. This design helps to reuse the same component multiple times, easy to debug and fix the issues. And has many advantages over procedure oriented design.
10.2.23 Virtual Machines and containers
Virtual Machine is a software, that gives the user a feel that he is the owner of the hardware. But in reality that hardware will be shared by many users.
Containers: It is a way to run an application along with it’s dependency in an isolated environment.
Publisher Subscriber model is also called as Pub-Sub model in short. In this model, a publisher will broadcast the message without the knowledge of subscriber. A subscriber will be always listening to broadcast topic without the knowledge of who is publishing the message.
10.2.25 Map reduce
This concept is used to do distributed and parallel processing of big data.
10.2.26 Multithreading, Concurrency, locks, Synchronization.
These concepts are important in multithreading. In Java it comes built-in, while other languages like “c” need to depend upon platform for implementation.