“Imperative scripts tell a system how to build something step by step. Declarative playbooks specify what the final state must look like, letting the API handle the rest.”

At NTT Data, we automated complex NSX-T Data Center fabric deployments using Ansible playbooks.

Imperative vs. Declarative Automation

• Imperative (Legacy): Execute API call 1 to create router -> wait -> execute API call 2 to create interface -> wait -> bind interface.
• Declarative (NSX-T Policy API): Post a single unified JSON/YAML payload defining the end-state topology. The controller resolves dependency graphs automatically.

[!NOTE] Using the vmware.ansible_nsxt collection allows network teams to manage firewall rules, segments, and gateways using simple, human-readable YAML.

# # Declarative NSX-T Segment Provisioning Playbook
- name: Create Overlay Segment
  vmware.ansible_nsxt.nsxt_policy_segment:
    hostname: "{{ nsx_manager }}"
    username: "{{ nsx_user }}"
    password: "{{ nsx_password }}"
    display_name: "Seg-App-Production"
    tier1_id: "T1-Gateway-01"
    subnets:
      - gateway_address: "10.200.1.1/24"
    state: present

The Verdict

Key Takeaway

Adopt Declarative APIs for Infrastructure Automation.

Declarative playbooks reduce code complexity and eliminate manual state tracking. Use Ansible and the NSX-T Policy API to build scalable, self-healing network fabrics.