Day(-1),Day-0,Day-1,Day-2..N Configurations

[shash]

In the world of network automation, network function virtualization and cloud deployment it very common to come across terms like Day(-1) "Day-Minus-One", Day-0 "Day-Zero", Day-1 "Day-One", Day-2 "Day-Two" and Day-N "Day-N". This terms are widely used but not well defined, sometimes leading to misunderstanding and confusion.  This blog post is an attempt to arrive at an common understanding and definition of these terms. (feedback and comments are welcome).

Definitions

Device configuration can be classified as Day(-1), Day-0, Day-1 and Day 2..N based on when they are applied to the device.

Conventions /Best-Practices/Guidelines/Recommendations:

Technically, the classification of configuration into Day-0,1,2,N is based on when the configurations is applied rather than what the configuration is trying to do.

The terms Day-0,1,2, etc. are also used in IT operations and other cloud operations domain. In these domains the classification of configurations into Day (-1),0,1,2,N the definitions vary slightly.

• Day 0, 1, and 2 in IT and VMware infrastructure
• Experience Day 0, 1, 2 and N Operations @ PuppetConf - Cisco Blog

To align with the "general" understanding of the terms Day(-1),0,1,2,N, we recommend the following conventions.

Day(-1)	Initial configuration typically applied on power-on, boot-up. Information entered on serial consoles, buttons/switches on device Configurations that need knowledge of physical connectivity, typically entered by operators on the truck-roll ID of the Interface connected to the switch for example (assuming there is not automatic topology discovery method) Configurations that are considered per-requisite.
Day-0	Minimum configuration required to establish communication between device and service orchestration system.
Day-1	Configuration pushed by service orchestration system that are common to all Service instances. (example, NTP, Syslog, SNMP Trap destination etc.)
Day-2..N	On-Going configurations pushed on the device for day-to-day operations. Configurations pushed to realize one instance of a service