System Design

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https://github.com/donnemartin/system-design-primer


Load Balancer
Web Server

Database
Cache


Scaling of hardware

Horizontal 
addition of new machine like new server pc

Vertical
addition of new hardwares in same machine like increasing ram and hdd


Performance vs scalability

  • If you have a performance problem, your system is slow for a single user.
  • If you have a scalability problem, your system is fast for a single user but slow under heavy load.


Availability vs consistency


CAP
In a distributed computer system, you can only support two of the following guarantees:
  • Consistency - Every read receives the most recent write or an error
  • Availability - Every request receives a response, without guarantee that it contains the most recent version of the information
  • Partition Tolerance - The system continues to operate despite arbitrary partitioning due to network failures
Networks aren't reliable, so you'll need to support partition tolerance. You'll need to make a software tradeoff between consistency and availability.

CP - consistency and partition tolerance

Waiting for a response from the partitioned node might result in a timeout error. CP is a good choice if your business needs require atomic reads and writes.

AP - availability and partition tolerance

Responses return the most recent version of the data available on the a node, which might not be the latest. Writes might take some time to propagate when the partition is resolved.



Availability patterns

There are two main patterns to support high availability: fail-over and replication.

Active-passive

With active-passive fail-over, heartbeats are sent between the active and the passive server on standby. If the heartbeat is interrupted, the passive server takes over the active's IP address and resumes service. Active-passive failover can also be referred to as master-slave failover. Heartbeat application take care of the activation of the passive server when active is dead for any reason and keeps running passive until active is not recovered.

Active-active

In active-active, both servers are managing traffic, spreading the load between them.
If the servers are public-facing, the DNS would need to know about the public IPs of both servers. If the servers are internal-facing, application logic would need to know about both servers.
Active-active failover can also be referred to as master-master failover.
Content Delivery Network

A content delivery network (CDN) is a globally distributed network of proxy servers, serving content from locations closer to the user. Generally, static files such as HTML/CSS/JS, photos, and videos are served from CDN.

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