Avoiding Cold Start on Servless Microservice Architecture

Question

I have a microservice project with 20 spring-boot projects using serverless lambda functions. The app is pretty slow on start because of the cold start.

I was thinking about calling a HTTP endpoint e.g. /warmup that basically calls all the lambdas of all the projects on login and every 20 minutes or whatever. Is this a proper way to do it? I don't even know where to put the /warmup endpoint because each project has it's on lambda functions and I would need to add all the names manually.

Any help on the proper solution?