Apache Traffic Server

HTTP/2 Server Push

Masakazu Kitajo maskit@apache.org

What is Server Push?• One of the features of HTTP/2

• Allows sending resources to a client before the client requests them

• Avoids additional round trips

• May reduce time to first paint

• if we could use it wisely

How does it work?

Server Push

GET /index.html

GET /index.html

Client Intermediate Origin server

index.html

index.html

How can we use it on TS?• TSHttpTxnServerPush

• Introduced since 7.0

• Experimental

• An example plugin is available

#include <ts/experimental.h>

void TSHttpTxnServerPush(TSHttpTxn txnp, const char *url, int url_len)

What will happen inside?Client Http2Stream PluginHttpSM

TSHttpTxnServerPush()

hook->invoke()

Http2ClientSession

send_push_promise_frame()PUSH_PROMISE

HEADERS

send_request()handleEvent()

send_request()handleEvent()

new_transaction()

new_transaction()

hook->invoke()

What will be a problem?

Server Push

GET /index.htmlGET /index.html

?We don’t know which resources we should push.

The client may already have the resource. The push may delay the response from an origin.

What can we do?• Use Manifest files

• Use Link header

• Use Link element in a HTML document

• Use Cache Digests (a.k.a CASPER)

• Also needs client side implementation

• Use AI (machine learning)

Simple

Complex

Future plan

• Add experimental plugins

• Add Server Push metrics (maybe 7.1.0)

• Brush up the API

• Show some results in the next summit

Summary• Server Push MAY increase performance

• Server Push CAN decrease performance

• Server Push API is available since TS 7.0

• Server Push may be too complicated for human beings

WE NEED YOUR FEEDBACK!

Thank you

References• HTTP/2 Server Push

• https://tools.ietf.org/html/rfc7540#section-8.2

• Link header & Link element

• https://www.w3.org/TR/preload/

• Cache Digests

• https://tools.ietf.org/html/draft-ietf-httpbis-cache-digest-00

• Akamai - Are you ready for HTTP/2 Server Push?!

• https://blogs.akamai.com/2016/04/are-you-ready-for-http2-server-push.html

• Cloudflare - Announcing Support for HTTP/2 Server Push

• https://blog.cloudflare.com/announcing-support-for-http-2-server-push-2/

• Fastly

• https://www.fastly.com/blog/announcing-limited-availability-http2