HTTP Partial POST Replay

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httpbis Working Group                                        A. Frindell
Internet-Draft                                                  Facebook
Intended status: Informational                             June 28, 2019
Expires: December 30, 2019

                        HTTP Partial POST Replay


   This memo introduces a method of exchanging HTTP [RFC7230] messages
   between a web server and a cooperating intermediary - such as a
   reverse proxy load balancer - that enables faster restarts for the
   web server with minimal disruption for users.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on December 30, 2019.

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Frindell                Expires December 30, 2019               [Page 1]
Internet-Draft                  HTTP-PPR                       June 2019

1.  Introduction

   Web servers need to drain traffic periodically for configuration
   changes, software updates and maintenance.  As continuous deployment
   becomes more common, the frequency of such events increases.  When a
   server shuts down, it chooses whether to let all existing requests
   run to completion, or abort some or all in-progress requests.
   Aborted requests lead to poor user experiences including error
   messages or additional latency while the request is resent.  Partial
   POST Replay makes it possible to eliminate this class of errors by
   handing off in-process requests to another server within a

1.1.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Partial POST Replay

   This section describes the Partial POST Replay mechanism for handing
   off a request with a partially transferred entity body to another
   server instance.

2.1.  Response Message

   When the server begins restarting, it responds to any unprocessed
   requests with incomplete entity bodies with a new 3xx status code
   (TBD).  The HTTP/1.1 status message is Partial POST Replay.  Once
   this status is sent the server MUST NOT process this request other
   than is specified in this document.

   The server MUST have prior knowledge that the intermediary supports
   Partial POST Replay before sending the 3xx response.  If a server
   sends this response to an intermediary that does not understand it,
   the response will likely be forwarded back to the client.

2.1.1.  Response Headers

   Each request header is echoed in the response message with the prefix
   "Echo-".  For example, the "User-Agent: Foo" request header would be
   included in the response as "Echo-User-Agent: Foo".  HTTP/2 [RFC7540]
   and HTTP/3 {{?HTTP3} request pseudo-headers (beginning with ':') are
   echoed in the response message with the prefix "Pseudo-Echo-", and
   with the ':' removed.  For example, ":path: /" is echoed as "pseudo-

Frindell                Expires December 30, 2019               [Page 2]
Internet-Draft                  HTTP-PPR                       June 2019

   echo-path: /".  The server MUST NOT insert any Echo- or Pseudo-Echo
   headers in the response if the corresponding header was not present
   in the request.

   Because there might be request body bytes in flight to the server
   when the 3xx response is generated, the length of the response body
   is unknown.  The response SHOULD NOT include a "Content-Length"
   header (but will include a "Echo-Content-Length" header, if the
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