Do I need to replace servers on all websites after implementing CNAME?

[DhanA2]

I’m in the process of implementing CNAME for my organization. We have two websites—one is still using the old ontrdc.net server, and the other is set up with a new CNAME server, smetrics.example.com.

After implementing CNAME, do I need to replace the server on both websites, or can the old server continue to work on Website A while the new CNAME server is implemented on Website B? Essentially, if I enable CNAME, is it mandatory to replace the server on all websites and apps, or is it optional?

ccing: top contributors for quick response @Jennifer_Dungan  

Thanks for the wonderful support!

[Jennifer_Dungan · Accepted solution]

Hi @DhanA2,

While it's in your best interest to use a first party tracking server, you are not forced into switching all sites at once.

Let's say you have:

• www.domainA.com
• www.domainB.com
• subdomain.domainA.com
• etc

(two main domains, one subdomain on one of the main domains)

Technically, you would be better having the two domain As on the same first party (so that when you set cookies against .domainA.com they will be shared, but technically speaking if you roll them out a different times, it shouldn't impact you too badly... 

In some cases, I have "third-party" solutions that I cannot CNAME since I don't own the domain, it loads like domainA.thirdparty.com.... so it's not ideal, and I end up with third party cookies... but I still send these via smetrics.domainA.com.

Now, your domainB.com can be set up with a CNAME, or left on the generic tracking... but you'll get better results using first party implementation... but it certainly not mandatory.