In-Depth Investigation of CDN: Part 2
Discover how CDNs achieve content consistency using mechanisms like time-to-live and adaptive leases. Analyze optimal proxy server deployment strategies, including ISP placement. Evaluate the strategic decision to use CDN as a service vs. building a specialized private CDN, like Netflix Open Connect.
This lesson explores mechanisms for maintaining content consistency, strategies for deploying proxy servers, and the distinctions between third-party CDN services and specialized, custom-built CDNs.
Content consistency in CDN
Proxy servers must remain consistent with origin servers to prevent users from accessing stale data. Several mechanisms ensure data consistency depending on whether a Push or Pull model is used.
Periodic polling
In the Pull model, proxy servers periodically fetch updated content from the origin. This periodic polling can waste bandwidth when content changes infrequently. The model defines a time-to-refresh (TTR) interval that specifies how frequently proxies revalidate or fetch updates.
Time-to-live (TTL)
To reduce unnecessary refresh requests from fixed TTR intervals, the time-to-live (TTL) mechanism assigns an expiration time to each object. Proxies serve the cached object until the TTL expires. After expiration, the proxy revalidates the object with the origin. If the object has changed, the proxy retrieves the updated version; otherwise, it continues serving the cached copy and resets the TTL.
Leases
In this technique, the origin server grants a lease to the proxy. The lease defines a time interval during which the origin agrees to notify the proxy of any data changes. Once the lease expires, the proxy must request a renewal. This reduces message volume between the proxy and origin. ...