I am using Rackspace ubuntu cloud servers and I'm also using Rackspace CDN images for my static web contents. Sometimes I'll have to update some images/css in the CDN and they will not be reflected immediately. The CDN has an option TTL from the range 1 to 72 in hours. I am failing to understand what the TTL is about and what TTL number suits me best. Sometimes the URL of the CDN images change and when it happens? Anybody could help me please?
The CDN TTL says for how long your copy will remain in the CDN after being copied from the main repository. Selecting different values for TTL have several effects:
cost since you get to pay for the copying from the main repository. I would assume a low TTL would increase costs. I do not know if there is any charge to having data stored in the CDN.
if you change a file while it is already in the CDN, that change may take up to TTL hours before it is available via the CDN to users. A high TTL thus reduces flexibility.
speed/latency is also affected. If the data requested by a user is not available in the CDN, it has to first be copied there from the repository which takes some extra time.
In a project where the files where changing on average once a year or so I chose the maximum TTL of 72 hours.