ota overview guidance

Hi, please help with following for aws s3 ota with mqtt having freertos:

ota demo code flow. referring "https://github.com/espressif/esp-aws-iot/tree/release/beta/examples/ota/ota_mqtt" ota bootloader code availability what libraries are required for ota what are ram and flash usage for ota when programming esp, if 2 partitions are created say ota0 & ota1, are both partitions erased while programming from esp idf eclipse thanks