To get a Rocket.Chat instance running, you need to pay attention to the properties of the machine/hardware you have.
These requirements vary greatly with:
Number of concurrently active users
Number of actually connected devices per user
Activities of the users - solely text-based messaging take minimal resources; while file sharing and jpg uploads will consume more resources, this is because a set of computations has to be done on these files
Bot or integration activity level; different bot and/or integrations have different requirements
The following are sized for the minimal cost deployment unit available for bare-metal server and cloud VPS.
The above minimal hardware configuration is ideal for corporate or groups with up to 1,000 users, up to 300 concurrently active, and moderate levels of mixed uploads, sharing, and bot activities.
VPS(Virtual Private Server)
A virtual private server is a virtual machine sold as a service by an Internet hosting service or cloud provider.
Single-core (2 GHz)
1 GB RAM
30 GB of SSD
The above minimal virtual configuration, when not over-provisioned by the provider, is ideal for small deployments of up to 200 users, up to 50 concurrently active, and a minimal level of mixed uploads, sharing, and bot activities.
Dual-core (2 GHz)
2 GB RAM
40 GB of SSD
The above virtual configuration, when not over-provisioned by the provider, can accommodate small deployments of up to 500 users, up to 100 concurrently active and moderate levels of mixed uploads, sharing, and bot activities.
Really Small Office Server
Raspberry Pi 3 or Pi 2
4 cores 1 GB memory
32 GB SD card ($15)
The above minimal configuration can accommodate a small office or group of up to 50 users and up to 25 concurrently active and moderate levels of mixed uploads, sharing, and bot activities. This is based on a managed MongoDB service (such as mlab.com). Running mongo local to a Pi is not recommended at this time.