Moving between different CDN providers

Congratulations, you are switching CDN providers. Whether you are a new Globaldots customer moving to a new platform, or you are an ex-customer moving away, or even completely not in any relationship with us, there are some things you need to know and things you will have to do. 

If one of our Sales Engineers was involved, then we already helped you to select the correct platform, helped you with performance benchmarks, and went over the economics. The following list deals with the actual moving between platforms. With a little preparation, this is done with zero downtime and full business continuity. 

Verify the configuration

Different CDN platforms may behave differently. The default cache time may be different. Gzip may or may not be turned on. Query strings may or may not be part of the cache key. You don't want surprises, so it is best to test the new CDN before moving to full production. Globaldots engineers help our customers during this tricky phase. 

Modify your web code

If your current usage involves using CDN provided host names, like "a123456.cloudfront.net" or "abc.akamaized.net", then changing a CDN mandates changing those links. 
We recommend using host names from your own domain, which can be defined as DNS CNAME to the CDN names. When using CNAME you don't have to modify your code if you switch to another CDN. 

Prepare SSL certificates

Depending on your CDN contract, you may have to provide a certificate, CA bundle and private key. On other cases you will have to approve adding your host names to an existing CDN managed SAN certificate. The approval is usually done via email to admin@yourdomain.com

Test

And test again. 

Have at least 3 days of concurrency on both CDN platforms

Although all of the Internet should respect content TTL and DNS TTL, our experience is that it sometimes takes more than the defined time for the traffic to subside. 

Reduce the DNS TTL on the host names

Before the switch, reduce the DNS TTL to a few minutes, so that rollbacks are easily done. 

Prepare the origin servers for a traffic spike

Your current CDN was providing some caching, shielding your origin servers from the major part of the traffic. The new CDN's cache is not warm yet, so your origin will see a traffic spike. 

Change the the host names DNS CNAME

This is the actual move. We reduced the risk by reducing the TTL and being able to fail over to the old settings. It never happened to me but it is good to be prepared. 

Monitor the new CDN for errors

Be ready and vigilant for 4xx errors or even 5xx errors. 4xx mean that the content is misconfigured, and 5xx mean that there is a major problem on your origin or in the connection between the CDN and your origin. We can help you with our monitoring tools. 

Monitor your old CDN for incoming traffic

The traffic should drop, but persistent traffic may still exist and should be investigated. 

Increase the DNS TTL on the host names

Get it back to the normal value to improve performance and reduce costs.