One powerful server or two medium ones?

Question

Network administration

There is a service that collects information from other services around the clock. Everything is located on one server - both the database and the project code and information collection services. Because of the services, the system is loaded and the site slows down.
There are 2 options - horizontal and vertical scaling. What is the best way to organize all this? The data that is collected from other services is not critical, that is, the speed of their collection is not critical. This option comes to mind: 2 servers with two databases and replication in order to write to one server and read from another. The one where to write on the same server with scripts to collect information. Second server for users and base for reading. But I have a bad idea how to work with users in this case, where to write their information? What if they send a message to one server and read from another?
In general, advise the easiest way to improve this.

Answer 1

If you already have software, then you need to look at it. Can you divide the software in a painless way into 2 parts.
If we were talking about development from scratch - two separate servers would be appropriate.
And just doing database replication is a bad idea.
UPD
I would start with profiling - identifying the bottleneck.
Where exactly slows down, because of what? Whether it's CPU and/or RAM usage, network load, or performance issues with the DBMS.

Answer 2

1 powerful without options