Raise the Keep-Alive idle timeout to 100 seconds #261
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Heroku's Router 2.0 now supports Keep-Alive connections: https://www.heroku.com/blog/tips-tricks-router-2dot0-migration/#keepalives-always-on https://devcenter.heroku.com/articles/http-routing#legacy-router-and-router-2-0 Gunicorn supports Keep-Alive connections, and so now if an app is using Router 2.0 connections between the router instances and the app will be kept alive. However, gunicorn's default `keepalive` idle timeout setting is only 5 seconds: https://docs.gunicorn.org/en/stable/settings.html#keepalive This is shorter than the 90 second Router 2.0 keep-alive timeout: https://devcenter.heroku.com/articles/http-routing#keepalives As such: (a) This causes connections to be closed sooner than they need to be (as noted in the gunicorn docs, the default 5 seconds is more suited for cases where many clients are connecting directly to gunicorn, rather than gunicorn being behind a load balancer). (b) there is a possibility of a race condition whereby gunicorn starts initiating the closing of an idle Keep-Alive connection just at the moment that the Heroku Router sends a new request to it. If this occurred, that new request could fail. This race condition isn't unique to Heroku or gunicorn, but applies to any load balancer/app server combination that supports Keep-Alive. For example, see AWS' explanation about this in their ELB docs: https://docs.aws.amazon.com/elasticloadbalancing/latest/application/edit-load-balancer-attributes.html#connection-idle-timeout Therefore, the gunicorn idle timeout has been raised from 5 seconds to 100 seconds, so it is greater than the Router's idle timeout - ensuring that the router is always initiating connection closing: https://docs.gunicorn.org/en/stable/settings.html#keepalive GUS-W-18319007.
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For consistency with the timeout chosen by other languages since #261 landed: - heroku/heroku-buildpack-php#823 - heroku/ruby-getting-started#190 GUS-W-18319007. Signed-off-by: Ed Morley <501702+edmorley@users.noreply.github.com>
edmorley
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For consistency with the timeout chosen by other languages since #261 landed: - heroku/heroku-buildpack-php#823 - heroku/ruby-getting-started#190 GUS-W-18319007. Signed-off-by: Ed Morley <501702+edmorley@users.noreply.github.com>
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Heroku's Router 2.0 now supports Keep-Alive connections:
https://www.heroku.com/blog/tips-tricks-router-2dot0-migration/#keepalives-always-on
https://devcenter.heroku.com/articles/http-routing#legacy-router-and-router-2-0
Gunicorn supports Keep-Alive connections, and so now if an app is using Router 2.0 connections between the router instances and the app will be kept alive.
However, gunicorn's default
keepaliveidle timeout setting is only 5 seconds:https://docs.gunicorn.org/en/stable/settings.html#keepalive
This is shorter than the 90 second Router 2.0 keep-alive timeout:
https://devcenter.heroku.com/articles/http-routing#keepalives
As such:
(a) This causes connections to be closed sooner than they need to be (as noted in the gunicorn docs, the default 5 seconds is more suited for cases where many clients are connecting directly to gunicorn, rather than gunicorn being behind a load balancer).
(b) there is a possibility of a race condition whereby gunicorn starts initiating the closing of an idle Keep-Alive connection just at the moment that the Heroku Router sends a new request to it. If this occurred, that new request could fail.
This race condition isn't unique to Heroku or gunicorn, but applies to any load balancer/app server combination that supports Keep-Alive. For example, see AWS' explanation about this in their ELB docs:
https://docs.aws.amazon.com/elasticloadbalancing/latest/application/edit-load-balancer-attributes.html#connection-idle-timeout
Therefore, the gunicorn idle timeout has been raised from 5 seconds to 100 seconds, so it is greater than the Router's idle timeout - ensuring that the router is always the one initiating connection closing (and the router will know to not send new requests to a connection it's in the middle of closing).
GUS-W-18319007.