Add SSL Certificates Can Cover Multiple Domains as a devops til

README.md

@@ -9,7 +9,7 @@ and pairing with smart people at Hashrocket.
 
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-_867 TILs and counting..._
+_868 TILs and counting..._
 
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@@ -117,6 +117,7 @@ _867 TILs and counting..._
 - [Reload The nginx Configuration](devops/reload-the-nginx-configuration.md)
 - [Resolve The Public IP Of A URL](devops/resolve-the-public-ip-of-a-url.md)
 - [Running Out Of inode Space](devops/running-out-of-inode-space.md)
+- [SSL Certificates Can Cover Multiple Domains](devops/ssl-certificates-can-cover-multiple-domains.md)
 - [Wipe A Heroku Postgres Database](devops/wipe-a-heroku-postgres-database.md)
 
 ### Elixir

devops/ssl-certificates-can-cover-multiple-domains.md

@@ -0,0 +1,10 @@
+# SSL Certificates Can Cover Multiple Domains
+
+When registering an SSL certificate, you can list multiple domains to be
+covered by it.
+
+One use case is registering a certificate that covers both the apex domain
+(`example.com`) and all subdomains using a wildcard (`*.example.com`). The
+wildcard alone will not cover `example.com`. If you want `example.com`,
+`www.example.com`, `blog.example.com`, etc. covered under the same certificate,
+then you'll need to include both the apex and wildcard domains.