Firebase Hosting can connect to your own custom domains, like
myrealtimeapp.example.com. Firebase Hosting provisions an SSL
certificate for your domain and serves your content over a global CDN.
Set up your domain for Hosting
Before connecting a custom domain, complete the "Get Started" wizard from your project's Firebase Hosting page. This Hosting page is where you'll see a history of deploys and manage connected domains.
From your project's Hosting page, click Connect Domain.
Enter the custom domain that you'd like to connect to Firebase.
Optionally, you can also check the box to configure a redirect of all requests on the custom domain to another specified domain.
Click Continue to initiate the validation process. Then, if requested, verify your domain ownership by following the on-screen instructions.
These steps ensure that your domain hasn't already been linked with a Firebase project and that you own the specified domain.
To complete the custom domain setup, you can use the Quick Setup mode in most cases. Point the DNS A records for your domain to Firebase Hosting, and we will provision an SSL certificate within a few hours.
However, if you already have a site running on another hosting provider and need a zero-downtime migration, then select Advanced Setup from the setup mode dropdown list. For the Advanced Setup workflow, follow the on-screen instructions either to update your domain's DNS TXT records or to upload a file to a specified location on your existing site. After verification is complete, you can safely point your DNS A records to Firebase Hosting.
Note that, for your custom domain, if your DNS records have A records or CNAME records that point to other providers, we are unable to provision an SSL certificate.
Wait for SSL certificate provisioning
After we verify domain ownership, we provision an SSL certificate for your domain and deploy it across our global CDN. This process can take several hours.
Your domain will be listed as one of the Subject Alternative Names in the FirebaseApp SSL certificate, which is publicly viewable. While the domain is provisioning, you might see an invalid certificate that does not include your domain name. This is a normal part of the process and will resolve after your domain's certificate is available.