You can enable Keep Alive Headers via the CloudNS plugin available in our cPanel.
CloudNS -> Configure -> Application Settings
Then, you will see a header of ‘Content Optimization’ – the first option in that list is the ‘set expires header’ flag which when enabled will enable the keep-alive for you.
Bolt-Cache Expires Headers
If you have enabled any of the caching methods available via the Bolt-Cache plugin, then the expires headers will already be set.