Java is one of the most popular programming languages for years. Many enterprise companies still heavily use Java programming language and have legacy applications written in Java. But when it comes to AWS Lambda (or serverless in general), it has some challenges and cold start is the most infamous one. This is one of the challenges they face when they want to migrate to AWS Lambda as rewritten all the applications with another programming language like Node.js, Python or Go may not be feasible for them.
Suppose you want to buy a ticket to a concert of your favorite band and you know that the tickets are running out. You need to open your computer, wait for the launch of the browser, go to the website of ticket sales, see there is only one ticket remaining, and click to buy. Then boom, “Sold out” is the phrase you are going to hate for a while. We are sad to say but you are “cold started”. You would have been able to catch the last ticket if your browser window was open, showing the website, and ready for you to click the “buy” button. You should have kept your computer warm to buy this ticket.