System Design

-
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.

Comments

Post a Comment

Popular posts from this blog

Thread & Locks

-
Image
Threads Threads are subunits of processes, which can be scheduled independently by the operating system scheduler. Multiple threads can be executed at the same time on a single CPU core. The operating system assigns small slices of computing time to each thread, so that it seems to the user as if multiple tasks are executed at the same time. If multiple CPU cores are available, then multiple threads can be executed truly in parallel. We can either use the POSIX thread API, or the Objective-C wrapper around this API, NSThread. NSThread is a simple Objective-C wrapper around pthreads. Grand Central Dispatch With GCD you don’t interact with threads directly anymore. Instead you add blocks of code to queues, and GCD manages a thread pool behind the scenes. GCD decides on which particular thread your code blocks are going to be executed on, and it manages these threads according to the available system resources. This alleviates the problem of too many threads being cre...
Read more

Opengl-es Buffer

-
Image
Framebuffer A  Framebuffer  is a collection of buffers that can be used as the destination for rendering. OpenGL has two kinds of framebuffers: the  Default Framebuffer , which is provided by the  OpenGL Context ; and user-created framebuffers called  Framebuffer Objects  (FBOs). The buffers for default framebuffers are part of the context and usually represent a window or display device. The buffers for FBOs reference images from either  Textures  or  Renderbuffers ; they are never directly visible. Default Framebuffer The Default Framebuffer is the Framebuffer that OpenGL is created with. It is created along with the OpenGL Context. Like Framebuffer Objects , the default framebuffer is a series of images. Unlike FBOs, one of these images usually represents what you actually see on some part of your screen. Framebuffer Object FBO contains a collection of rendering destinations; color, depth and stencil buffer. These logical buff...
Read more

Kernel Startup

-
Image
BootLoader GRUB Version 2 (GRUB) Stage 1 :  boot.img  is stored in the master boot record (MBR) or optionally in any of the  volume boot records  (VBRs), and addresses the next stage by an  LBA48  address (thus, the 1024-cylinder limitation of GRUB legacy is avoided); at installation time it is configured to load the first sector of  core.img . Stage 1.5 :   core.img  is by default written to the sectors between the MBR and the first partition, when these sectors are free and available. For legacy reasons, the first partition of a hard drive does not begin at sector 1 (counting begins with 0) but at sector 63, leaving 62 sectors of empty space not part of any partition or file system, and therefore not prone to any problems related with it. Once executed,  core.img  will load its configuration file and any other modules needed, particularly  file system  drivers; at installation time, it is generated from...
Read more