Infrastructure
Building blocks
Infrastructure questions test whether you can place a component in the right layer. Physical components include servers, storage arrays, switches, routers, firewalls, wireless access points, cabling (copper twisted pair for short runs, fiber for distance and immunity to interference), racks, power (UPS, PDU), and cooling. Logical components include IP addressing, DNS (name to IP), DHCP (automatic addressing), VLANs, and subnets.
Virtualization and cloud
A hypervisor lets many virtual machines share one host; Type 1 runs on bare metal (typical in data centers), Type 2 runs on a desktop OS. Containers package an app with its dependencies but share the host kernel, so they start faster and weigh less than VMs. Know the service models: IaaS gives raw compute, storage and network you manage yourself; PaaS gives a managed runtime where you deploy code but not the OS; SaaS delivers a finished application. Deployment models are public, private, hybrid, and community.
Storage and resilience
NAS is file-level storage on the LAN; SAN is block-level storage over a dedicated network. RAID improves availability or performance but is not a backup. Redundancy (dual power supplies, RAID, clustering) addresses availability; backups address recovery. The 3-2-1 rule: three copies, on two media types, with one offsite.
Worked example
A team wants to push code without patching servers or managing an OS. IaaS would leave the OS to them, and SaaS would deliver a finished app, so PaaS is the fit.
Traps
- Confusing a router (between networks) with a switch (within a LAN) or a hub.
- Assuming RAID replaces backup.
- Calling anything on-premises a private cloud; the defining trait is dedicated tenancy and control.