I have my client's domain registered via 1and1.com
To connect the domain to the Firebase hosting, Firebase asks me to add TWO A records with 2 IPs. In 1and1 we can only add ONE A record. Yesterday Firebase sent me this message by mail
Please re-verify ownership of www.*******.com on *******-website. The previous verification for this domain has been invalidated. You have 1 day to re-verify ownership of www.*******.com before it is removed from Firebase Hosting, which will stop all content from being served from the domain. Please visit the Firebase Hosting Panel to start the re-verification process.
Today the website was disconnected.
I reconnected the domain to the Firebase hosting through the Firebase control panel and got the website up again. But the Firebase control panel says it still needs setup
I am sure it will disconnect it again soon. How to solve that? (I already called 1and1 and they told me no way I would be able to add another A record.)
I set up in the same way a website (https://lasi17.snola.es/) and it seems to work with only one A record pointing out to the Firebase IP.
In my case, I just changed the option in Hosting -> Domains -> Your custom domain (in my case lasi17.snola.es) -> Process traffic in this domain ("Edit" under the kebab menu). After that, the domain works as usual with only one A record configured.
来源：https://stackoverflow.com/questions/43106745/firebase-hosting-with-only-one-a-record