[opensource-dev] CDN

[Henri Beauchamp]

On Fri, 23 Mar 2018 14:51:30 -0500, Nicky Perian wrote:

> What is the procedure for determining which CDN node is use for viewer
> instance.

CDN server IPs are served by your DNS, the latter being updated with the
closest CDN server. I.e. if you live in one country and use a DNS hosted
in another, you get the IP of the CDN server of that other country instead
of yours...
The assumption is that people are likely to use a DNS close to their home
(usually, they use their ISP's DNS).

E.g. for me (in France) with my ISP's DNS:
# nslookup maps-cdn.agni.lindenlab.com
maps-cdn.agni.lindenlab.com     canonical name = secondlife.edgesuite.net.
secondlife.edgesuite.net        canonical name = a336.d.akamai.net.
Name:   a336.d.akamai.net
Address: 88.221.83.50
.../...

# whois 88.221.83.50
inetnum:        88.221.83.0 - 88.221.83.255
netname:        AKAMAI-PA
descr:          Akamai Technologies
country:        EU (actually, 88.221.83.0/8 is in France)
.../...

Now, via dnscrypt (with a DNS in Canada):

# nslookup maps-cdn.agni.lindenlab.com
maps-cdn.agni.lindenlab.com     canonical name = secondlife.edgesuite.net.
secondlife.edgesuite.net        canonical name = a336.d.akamai.net.
Name:   a336.d.akamai.net
Address: 23.15.4.17
.../...

# whois 23.15.4.17
NetRange:       23.0.0.0 - 23.15.255.255
CIDR:           23.0.0.0/12
NetName:        AKAMAI
.../...
Country:        US

> Then, how do you determine which assets are present on that CDN and not
> present in the viewer?

Not sure what you mean, here... The viewer requests an asset to the CDN
server and if the asset is already cached in the latter, it is immediately
transfered to the viewer, else the CDN server asks to the upstream server
for that asset, caches it and transfers it to the viewer.

Henri.