Re: [Webpush] Message expiration (TTL) and Negative Acknowledgements

[jr conlin <[e-mail]>]

On 10/14/2015 2:37 PM, Martin Thomson wrote:
> On 14 October 2015 at 14:09, JR Conlin <[e-mail]> wrote:
>> 429: This will allow the server to apply "back pressure" to the
>> application service in cases where there may be too many incoming
>> messages in a short period of time. This response would carry a
>> RETRY-AFTER response header indicating the number of seconds that should
>> elapse before the remote server should retry transmission of the message.
>
> How is that different from 503?

Traditionally (as if that's a thing for the web) 503 tends to be used by
intermediary services like load balancers to indicate that "something's
amiss with the box I normally talk to". Since it's a 500 class error, it
indicates an error state possibly from outside the server. 429 was
identified as part of https://tools.ietf.org/html/rfc6585 to be used
more as a rate limiter and carries with it the "Retry-After" response
header indicating how long the requester should wait before retry. It's
a 400 class error, which means it should come from the responding server.

Either would work, of course, but it may be that programmers can take
advantage of pre-existing handlers in libraries to do the back-off for
them, rather than have to code the response themselves.