They were on azure and in 2018 microsoft threatened to expel them from the platform after which point they built and migrated to their own hosted systems.

https://news.gab.com/2020/09/30/gab-just-became-resilient-in-a-big-way/

https://www.gizmodo.com.au/2018/08/microsoft-threatens-to-stop-hosting-gab-the-worst-social-network-over-anti-semitic-threats-of-violence/

Both gab and parler have gotten lots slower over the last 24h with all the twitter bans leading to a large migration to these systems, gab appears to be worse off though in their favour it looks like they will be able take the hits better due to already removing the hosted-platform vulnerability that parler is still susceptible to.

I'm sure next up will be attempts to steal their domain (we saw this happen to 8ch) and threats (ddos, extortion etc) against wherever their systems are located and the people that own the network IP blocks.