These are usually referred to as alias records since they usually map an alias to its canonical name. The name server does handle these queries differently from an A record. When a name server looks up a name and finds a CNAME record, it replaces the name with the canonical name and looks up the new name. This allows you to point multiple systems to one IP without specifically assigning an A record to each hostname. If your IP was ever to change you would only have to change one A record.
How to Configure
1. Navigate to Managed DNS
2. Select your Domain
3.Click the Plus Button
Under “CNAME Records” click the plus sign to add a new record.
4. Enter CNAME values
We will add a CNAME record to the domain example.io for www.example.com which maps to the root record of the domain name. To alias to the root record of the domain name, you leave the data value blank. Finally, click Submit.
A. Name: This will be the host for your domain which is actually a computer within your domain. Your domain name is automatically appended to your name. If you are trying to make a record for the system www.example.com. Then all you enter in the textbox for the name value is www.
B. Alias to: This is the system that your host (that your name value defines) will point to. This value should always be an A record. This should not be a CNAME record as an alias to an alias is not correct. Your domain name is automatically appended to your value (if it does not end it a dot). If you are trying to make an alias to mail.example.com.. Then all you enter in the textbox for the Data value is mail.
C. TTL: The TTL (Time to Live) is the amount of time your record will stay in the cache on systems requesting your record (resolving nameservers, browsers, etc.). The TTL is set in seconds, so 60 is one minute, 1800 is equal to 30 minutes, etc..
Systems that have a static IP should usually have a TTL of 1800 or higher. Systems that have a dynamic IP should usually have a TTL of 1800 or less.
The lower the TTL the more often a client will need to query the name servers for your host’s (record’s) IP address this will result in higher query traffic for your domain name. Whereas a very high TTL can cause downtime when you need to switch your IPs quickly.
Best Practice Tip If you plan on changing your IP you should set your TTL to a low value a few hours before you make the change. This way you won’t have any downtime during the change. Once your IP is changed you can always raise your TTL to a higher value again.
Map an internal FQDN to another internal FQDN
You can also create an alias for one hostname to the hostname of an A record. Here we create the CNAME record smtp.example.com and alias it to the A record mail.example.com.
Map an FQDN to an external domain
Finally, you can create an alias for a hostname to another external domain. Here we create an alias for search.example.com to google.com.
Example 1 – CNAME to record within the same domain: