The Magento application have option to make site in maintance mode during maintaining, upgrading, or reconfiguring our site.
Magento detects maintenance mode as follows:
var/.maintenance.flag does not exist, maintenance mode is off and Magento operates normally. Otherwise, maintenance mode is on unless
var/.maintenance.ip can contain a list of IP addresses. If an entry point is accessed using HTTP and the client IP address corresponds to one of the entries in that list, then maintenance mode is off.
Add allowed IP during maintanace mode
php bin/magento maintenance:allow-ips xxx.xxx.xxx.xxx
Enable maintanace mode
php bin/magento maintenance:enable
Disable maintance mode
php bin/magento maintenance:disable
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