Start with measured load
For an existing app, review CPU, memory, disk use and peak requests. For a new project, start with software requirements and allow room for the database, logs and backups.
When dedicated hardware helps
Compare VPS plans for small websites, development and lightweight APIs. Consider dedicated hardware for sustained demand or isolation; a hardware change does not automatically fix slow queries or application bottlenecks.
A single server is not high availability
Buying a server does not set up managed databases, off-site backups or failover. If extended downtime is unacceptable, design the recovery process before deciding how many machines to buy.
Rehearse recovery
Check DNS, certificates, application startup and database connections. Restore a backup into a separate test environment and document the procedure rather than overwriting production data.