Saturday, December 10, 2011

Book Review: Scalability Rules: 50 Principles for Scaling Web Sites

If this article hurts anyone's copyright, let me know and I'll remove it.

Scalability Rules: 50 Principles for Scaling Web Sites - on Amazon

This book was a nice read, I didn't get overexcited about it.

The book is talking about what can and can't, what should and shouldn't be done to make your application and services easier to scale, I'm including a little summary so you can judge for yourself if you want to read it.

The following is my understanding and summary of the rules and do not completely correspond with the author's, I've omitted a few rules which looked redundant to me.

Rule 1 - Write simple programs, complicated programs are hard to maintain and hard to add scaling logic to.
Rule 2 - Design the program to scale up front, its cheaper than trying to scale a finished product.
Rule 4 - Balance CDNs and DNS lookups.
Rule 5 - Reduce objects, on HTML pages, CSS files, JS files, on page creation, in code etc', remember if an object is being created it also needs to be disposed of.
Rule 6 - Use a single hardware provider, less chance of collision between protocol implementations and standards. 
Rule 7 - Horizontally scale, for example, if you're using SOA, create some services and balance the load.
Rule 8 - Split the load of the program to different components.
Rule 11 - Use small abandundly available components rather than big specialized systems, e.g. horizontally scale.
Rule 12 - Design your data to be split across data centers.
Rule 13 - Design your application to utilize what clouds have to offer.
Rule 14 - Use RDBMS where best, NOSQL where best and file-systems where best, don't force one of them to be the other.
Rule 15 - Use firewalls on every important component you're using.
Rule 16 - Use log files, monitor them, analyze them.
Rule 17 - Don't check and read what your program just did, for example, read a file you just wrote or read a transaction you just committed.
Rule 18 - Avoid using redirects, its slowing the user's experience.
Rule 19 - Avoid state constaints.
Rule 21 - Implement expires headers, otherwise caching is limited.
Rule 22,23,24,25,26 - Cache ajax requests, pages, application object, db executions, service calls, use external cache storages like memcache.
Rule 27 - learn from everything, customers, etc'
Rule 28 - Don't rely on QA, the software engineers should do most of the testing, integrate tests into the program.
Rule 29 - Design to rollback your changes, not designing for it could be a disaster.
Rule 30 - Discuss failures, no need to blame, just learn from them.
Rule 31 - Check database relationships and constraints for load, cost, normalization, etc'.
Rule 32 - Use the right database locks where they are needed. page, row, table, schema, etc'.
Rule 33 - Do not use multiphase/two-phase commits.
Rule 34 - Avoid database cursors.
Rule 35 - Do not use select *, get only the data you need.
Rule 36 - Segregate program and data so if one part of the application goes down it doesn't take the whole system with it.
Rule 37 - Single points of failure (SPOFs) will fail, eliminate or plan for it.
Rule 38 - Avoid putting systems/components in series, slows things down and has the potantial of being a domino effect of failure.
Rule 39 - Add the ability to turn on and off features in your application without recompiling the program, if one coponent acts up, you can turn it off without affecting other components until its fixed.
Rule 40 - make everything as stateless as possible.
Rule 41 - Use cookies for state instead of server state.
Rule 42 - Use distributed cache for state, its easier to scale than application state.
Rule 43 - Use async calls instead of sync calls which freeze the program until something else is finished.
Rule 44,45 - Use message buses that can scale and only where the cost to perform the action is higher than the cost to process it via message bus.
Rule 46 - Avoid using 3rd party to scale your application, it might introduce more problems than it will solve.
Rule 48 - Don't use business intelligence in your transactions.
Rule 49 - design your application for monitoring, add logs, performance counters, etc'.
Rule 50 - don't blame anyone, to the user you're the one to blame, for example, if your hardware vendor is giving you a hard time solve it or replace them.

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