My journey started as a part-time web developer. A MySQL database, Php for backend, VueJs and jQuery frontend, scss for css and I'm done. So easy!
I was never thinking about scaling, rate limiting, timeout on those days, and normal site even does not need to care about such things unless they reaches that threshold.
Luckily, I got chance to work on a product which was requiring all of this. It was the first time when I got exposure to real scalable application with spike in traffic, Ahmedabad Shopping festival 2019.
Brief Intro of Ahmedabad Shopping festival
Ahmedabad Shopping festival was first digitally managed shopping festival of India hosted in Ahmedabad, Gujarat. Every customer were getting rewards and coupons for chance to win prize on making shopping during shopping hours.
Ahmedabad Shopping festival was consisting a web portal for retailers, a web portal for administrators of shopping festival and mobile application for shoppers.
All of this modules were needing access to database, sms module and push notification module and requests to each service could scale from 0 to massive amount at any time.
It was also required to be able to make deployment during shopping hours without having any downtime or any glitch in any of the module.
Issues and Resolutions
Ability to make deployments during shopping hours.
Our first and for most issue was ability to make a deployment during shopping hour without introducing any glitch. Glitch was not acceptable at all as It could affect result of lucky winner selection based on coupons issued.
This issue was solved using versioning with app engine servicesand traffic migration in conjunction with warmup request.
We were using sms and push notifications with all the modules. Sms service was capped by a rate limit per time period (X / sec ). Reaching that limit would have resulted in delivery failure of sms.
Sms were used for notifications to retailers and admins but, most importantly sms were also used for OTP for signup/sign-in in shopper facing app. So neither late not failure of sms delivery was acceptable at all.
Google cloud task was used as solution. All of the sms from different backend services were written to that queue which was optimised in way that it was sending messages at highest possible rate without exceeding limit.
Taking daily backup, loading data and processing to find lucky winner
This tasks were supposed to run daily on specified time. It was handled using cron jobs.
Giving as fast response as possible to every request
Shoppers were in count of thousands. During shopping hour request could making spikes that it reach the read limit per second of database. Therefor reading from the database was not a feasible one.
As solution memcache was used. For every incoming request we were first looking at memcache, if memcache does not have data then data was loaded to memcache and same time it was returned as response as well.
Here we found that data being sent to shopper were not going to be changed by any event or action of shopper other then his/her coupon counts. Most of the data was going to be static for the day,
There was only one request the first one of the day has to go to read the database, but we know that reading memcache is faster then reading database. So to make first request to read memcache as well, we started refreshing and reloading memcache before the first request of the day hits api.
So, technically were serving thorough only memcache through out the day without going to database for reading more then once in a day in normal scenario.
Data sent to shoppers were static and going to be unchanged for day long. As result we were caching data to the devices local storage for day that was reducing request to the api and loading data faster at same time.
So there were two caches used,
on cloud in form of memcache
second local storage at device level which significantly improved response time.
Architecture was designed to generate faster response with minimum usage of resource and without exceeding constrains imposed by third party service providers and cloud services (database & big-query ) itself.
Ahmedabad Shopping festival was the project which made me think as a person for whom things working is not enough, but the way it works is also matters.
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