How to scale a web application to a million users in 10 steps

1- Scale your server vertically, which means using a faster computer.
2- Place your database on another server, this will relieve the burden on your application server.
3- Add a load balancer and more backend servers (or basically scale horizontally)
4- Don't forget to add a firewall that will protect you from various attacks
5- Move expensive calculations to the front-end, such as rendering web pages. Use a content delivery network
6-Add read-only replicas for expensive queries or analytics
7-Cache expensive calculations or database queries
8-Divide monolith into microservices so you don't have to deploy every line of code on every machine and you can scale one part of your application independently of others
9-Use a queuing system to communicate between microservices where necessary
10-Start using non-relational databases such as Cassandra or elastic search, depending on the company.

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