Where is the "trick" in the next server setup?

Question

System administration

What is the disadvantage of this system or what is its similar cost if done "as usual"?

• We take shared hosting with "unlimited" number of databases, storage and traffic ($5) for static and database.
  
• We take a free or the cheapest vps for the balancer.
  
• We write code. We produce it on free heroku instances.
  
• We constantly ping instances so that they do not fall asleep.
  
• As a bonus, due to the ubiquitous presence of mysql on shared shares, and in many places, also with remote access, with the most minimal vps (say, 128-512 ram), is it possible to launch a replication master and distribute many shared hostings at free rates?
  

Most likely, somewhere here there is a fatal flaw, or is such a "system" built not for $5 per month, but for $20, but with much less effort?

PS If it helps in some way, let's imagine that we are making a spherical tweeter with cut functionality - everyone can read all the tweets, everyone can write their own tweet and post someone else's on their page. What will the infrastructure be in the first place?

Answer 1

What is the disadvantage of this system

It is impossible to answer this question without knowing the goals of such a system and the requirements for it.
It's like asking how much it costs to deliver a ton of cargo. Without knowing the dimensions of the cargo, distance, and a bunch of other factors, it is impossible to answer.

Answer 2

You will end up with an uncontrolled shit system, that is, without any guarantee that the user will receive an answer. The time of school hosting is gone.

Answer 3

Building such a system will be much more expensive than $20
latency between the balancer and slaves, as well as a random overload of slaves (cheap / free hosting is always bad) will make the response time large and unpredictable.
All hostings have real limits on everything - CPU, memory, connections to the database, script execution time, etc. are registered in TOS and for overuse you will either be evicted to a nafig / to an expensive tariff plan, or your account in the container will simply slow down wildly and it’s useless to you from a slave that sends requests sometimes and with delays of 5-30 seconds,
I can build this - but the picture immediately comes to mind: