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Connection reuse and coalescing

Aside from concurrent connections1, connection reuse and connection coalescing are also important concepts. They both have impact on latency and are considered when allocating your Aegis IPv4 addresses.

Implemented by HTTP/1.1, connection reuse describes multiple requests passing through one same connection (between one source IP:port and one destination IP:port). It is commonly the case even for simple websites nowadays.

Example

When a connection is initiated for shop.example.com, several embedded subresources may be requested - CSS, image files, advertisement, etc. This can mean hundreds of requests just for the website to load. Instead of having a one to one ratio of request per connection, a single connection is used for multiple requests.

With HTTP/2, requests can use the same connection even if they are for different domains.

Example

A connection initiated for shop.example.com can be used for requests for blog.example.com as well - as long as the requests have the same destination IP:port and the server TLS certificate is authoritative for both hostnames.

Refer to the Cloudflare blog post ↗ for further details.

Footnotes

  1. If you have one Aegis IP and two origins (A and B), this single Aegis IP can support 40,000 concurrent connections to origin A, while simultaneously supporting 40,000 concurrent connections to origin B. ↩