Scaling webservices- Its easy!!

Just recently i was asked to develop a massively scalable webservice for a client called FADU Bakery shop ;). I am also a software developer like you who does less but only i know!!. I explored the concepts involved in making a web service scalable and i am just trying to sharing it with you. Have fun and hope you like it. Your comment is always welcomed!!

When we talk of scalability it involves:

1. Application server scaling.

2. Database server scaling.

3. Memory scaling- Cache and MQ.

I am trying to explore each concepts respectively.

Application server scaling by cloning:

Usually our application servers are hidden behind a black box called load balancer. This load balancer evenly distribute the load onto the group of hidden app server with high probability using the intelligent algorithm based on time-stamp or loads. That means if User Mrs Ssoni interact with your service for the first time she may be served by server 5 and in second request is served by server 2 and may be in third request it again come to server5.

Ssoni always get the same result of her same request independent of which server she lands on. That gives us the first golden rule of scaling -'Every server should have same code base and should not store user data like profile pic or session data'. Otherwise imagine if Ssoni has checked some milk bread on server1 but in second request server is changed and the the milk-bread is not in her basket :(.

So what next... where to store this user data?

One among many solution is to store this user data in a centralize data storage accessible to all the application server or store this user data by scaling the memory of load balancer. It could be a database in load balancer or the persistence cache like redis or memcached. Please dont use the file based caching more frequently as it make auto scaling and cloning pain.

So far so good...But what about deployment on multi server?

How do you assure that the code changes is effectively on all app server. Dont worry this is tricky problem and already solved by multiple tools like Capistrano or you can write own script for that to show you are not lazy as me.

Now we are serving the same codebase from all app servers, we can now create an image file from one of these servers (AWS calls this AMI - Amazon Machine Image.) Use this AMI as a “super-clone” that all your new instances are based upon. Whenever you start a new instance, just do an initial deployment of your latest code and you are ready! Is not it simple enough...?

#database and memory will be in next blog ... soon!!

#Names are virtual.