> Please can someone clarify the exact behavior around Consistent Hash and unavailable parents?
It's not a background thread. It's the same thread/continuation of a regular request, but not every request, only after records.config proxy.config.http.parent_proxy.retry_time. It will make either parent.config max_simple_retries, parent.config max_unavailable_server_retries, or records.config proxy.config.http.parent_proxy.total_connect_attempts and records.config proxy.config.http.parent_proxy.per_parent_connect_attempts attempts each time, before marking down again for parent_proxy.retry_time. > we are seeing the retries on the originally hashed parent occur more often than we would expect. It sounds like you probably don't have those settings the way you want them. Note all those records.config settings are Overrideable, so you can set them per-remap with the Configuration Remap or Header Rewrite plugins, if you want. Links: https://docs.trafficserver.apache.org/en/9.1.x/admin-guide/files/records.config.en.html#proxy-config-http-parent-proxy-retry-time https://docs.trafficserver.apache.org/en/9.1.x/admin-guide/files/records.config.en.html#proxy-config-http-parent-proxy-fail-threshold https://docs.trafficserver.apache.org/en/9.1.x/admin-guide/files/records.config.en.html#proxy-config-http-parent-proxy-total-connect-attempts https://docs.trafficserver.apache.org/en/9.1.x/admin-guide/files/records.config.en.html#proxy-config-http-parent-proxy-per-parent-connect-attempts https://docs.trafficserver.apache.org/en/9.1.x/admin-guide/files/parent.config.en.html#parent-config-format-max-unavailable-server-retries https://docs.trafficserver.apache.org/en/9.1.x/admin-guide/files/parent.config.en.html#parent-config-format-max-simple-retries On Tue, Aug 17, 2021 at 9:40 AM Nick Dunkin <nick.dun...@vecima.com.invalid> wrote: > Hi, > > > > I have a question about Consistent Hash behavior when a parent is “down”. > This is ATS 7.1 > > > > The documentation states the following: “*If a parent is down, the > traffic that would go to the down parent is rehashed amongst the remaining > parents. The other traffic is unaffected. Once the downed parent becomes > available, the traffic distribution returns to the pre-down state.*” > > > > That second section implies that maybe: > > - A background thread is periodically retying the original hashed > parent, in order to mark it back *up* > - The original hashed parent is being retried on every access until it > is available again > > > > Please can someone clarify the exact behavior around Consistent Hash and > unavailable parents? The context here is that we believe we are seeing the > retries on the originally hashed parent occur more often than we would > expect. > > > > Many thanks, > > > > Nick > > > > *Nick Dunkin* > > Director, Software Engineering > > Manager – Architecture and New Product Introduction > > *o: * *+1 678.258.4071* > > *e:* nick.dun...@vecima.com > > > > [image: cidimage001.png@01D6CC8C.6FC5A580] > > >
