“Many people are now using the ESP8266 in its many guises (ESP-01S, Wemos D1, NodeMCU, Sonoff etc) for home automation systems. If you write your own code (as I do) updating each of these separately even via OTA (over the air) becomes a bit tedious.
My own system, for example has 8x ESP-01S, 6x Wemos D1, 4x Sonoff Basic 12x Sonoff S20, 2x Sonoff SV and a NodeMCU which share a common code base, so that’s 33 devices in all to update when I make a simple code change.
But there is an easier way: An “update server”. The excellent Arduino IDE + ESP8266 core has a library to do most of the work (ESP8266httpUpdate), but you need to know how to set up your own server to make it work.
This Instructable shows you how using a NODE-RED server, but the same logic applies to any server technology of your choice e.g. Apache + PHP etc”