Infrastructure and Automation
Automation tools and their signatures
Infrastructure as code (IaC) means describing desired state in files, versioning them, and letting a tool converge the system. Questions ask you to identify the tool from its defining traits.
Ansible is agentless, connecting over SSH (or WinRM) using Python, with YAML playbooks, inventories, and modules. Tasks are idempotent: running a playbook twice yields the same end state. Puppet uses a master/agent model with a manifest language; Chef uses agents with recipes and cookbooks in Ruby DSL. Terraform is declarative HCL that provisions infrastructure through providers and tracks real resources in a state file; plan previews and apply executes. SaltStack uses a master/minion model with states. Simpler scripting (Python with Netmiko or NAPALM) is imperative - you tell the device each step.
Orchestration coordinates multi-step workflows across systems; configuration management enforces per-device state; automation is the broad umbrella. Controller-based networking moves the control plane to a central brain (SDN), with southbound APIs to devices and northbound APIs to applications.
Model-driven programmability: YANG defines the data model, NETCONF (SSH 830) and RESTCONF (HTTPS) transport configuration, and model-driven telemetry pushes structured data at high rate instead of SNMP polling. Cisco NSO models services across vendors; Catalyst Center and Meraki provide intent APIs.
Trap: calling a script idempotent when it appends config each run, or assuming Ansible needs an agent. Rule of thumb: if it must run repeatedly without side effects, it must be idempotent - check state before changing it.