Collecting data for analyzing and troubleshooting has always been an important aspect in monitoring the health of a network.
Cisco NX-OS provides several mechanisms such as SNMP, CLI, and Syslog to collect data from a network. These mechanisms have limitations that restrict automation and scale. One limitation is the use of the pull model, where the initial request for data from network elements originates from the client. The pull model does not scale when there is more than one network management station (NMS) in the network. With this model, the server sends data only when clients request it.
To initiate such requests, continual manual intervention is required. This continual manual intervention makes the pull model inefficient.
A push model continuously streams data out of the network and notifies the client. Telemetry enables the push model, which provides near-real-time access to monitoring data.
Reference:
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus9000/sw/7- x/programmability/guide/b_Cisco_Nexus_9000_Series_NX- OS_Programmability_Guide_7x/b_Cisco_Nexus_9000_Series_NX- OS_Programmability_Guide_7x_chapter_011000.html