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Notes On Scalability

06 Feb 2021 . 4 mins : learning . Comments
#programming practices #tech #notes #systems #scalability

Around a month back I saw the CS75 Lecture on Scalability by David Malan. The write up contains the notes from the same that I wrote while revisiting the lecture.

  • SFTP is better than FTP - in the latter credentials are also sent as plain text.
  • VPS, on an abstract level, is a slice of the shared hardware with separate OS. Comparing to shared hosts, they share OS as well and hardware is not throttled per user.
  • Vertical scaling - get more ram, more processors, more space, etc. There is a cap on vertical scalability.
  • Processes usually happen in a sequential manner on a single core. With multiple cores, parallelism is achieved.
  • The advancement in vertical scalability has improved the accessibility of VPSes.
  • SSD » SAS » SATA HDD - order in terms of price and speed.
  • Horizontal scalability is achieved by using multiple machines - spanning the load on the level.
  • Load balancer distributes the traffic across multiple machines in horizontal scaling.
  • Private IP addresses cannot be directly reached by the internet.
  • Load balancing can happen on the basis of load, round robin, work distribution, etc.
  • There are caches on different levels - browser, system, etc. storing DNS queries, website scripts, etc.
  • In a scenario where separate hard drives are used in each machine, the session may break.
    • can be solved by having a separate micro-service for session connected to all machines
    • eliminates the redundancy since the micro-service is the bottleneck
  • Redundant Array of Independent Disks (RAID)
    • RAID 0 - two identical hard drives with strip writing; some data in 1, some in 2, and so on
    • RAID 1 - two identical hard drives with both having the same data
    • RAID 10 - 4 identical drives with both striping and cloning
    • RAID 5 - 5 identical drives with 4 in striping and 1 for cloning
  • A shared file server or database can solve the problem of cookies and sessions.
  • Database replication solves the problem of single point of failure for storage.
  • Storing the server name (present behind the load-balancer) also helps us in achieving sticky sessions.
  • PHP accelerators helps speed PHP server by caching the OPCODES.
  • Apache and other servers are highly optimized for serving static files.
  • Caching, in various forms, is usually a key-value store and useful for optimization of redundant operations.
    • MySQL has caching inbuilt.
    • Memcached is a memory cache.
    • Garbage collection kicks out data from cache based on some rule.
  • InnoDB supports transactions. There are other storage engines that provide different features.
  • Replication is all about keeping multiple copies of same data. Master(s)-slave(s) architecture is an example of the same.
  • A single level of micro-services is called a tier. Architectures are usually multi-tier.
  • Load balances work in pair in a active-active mode. They send heartbeats to each other all the time. In active-passive, passive comes in picture when there is no heart beat from active.
  • Partitioning is very common in databases - separation of data based on a high level attribute.
  • The concept of network redundancy comes into play to avoid hardware level of failure in the network connections.
  • Geography based load balancing is done on the DNS level, mostly.
  • SSL is usually offloaded at the load-balancer level to save cost, time, and complexity.
  • The principle of least privilege - only open those doors that people need to go through.
  • There’s always a trade-off - scalability is about finding balance based on requirements.

Nothing ever is perfect, there’s always a gotcha.


Your typical geek; Shivam can be found toiling hard through books (away from library) to find what she means by her actions :wink: Hard at work, and harder at drunk dancing, he loves to find ways to increase his productivity so he can invest time elsewhere. When he does get some time, and is in the mood, he writes few lines of code and some lines of rhymes :facepunch: