[GitHub] [trafficserver] rob05c commented on issue #8519: How long does ATS take to reinstate a downed parent?

[GitBox <gi...@apache.org>]

rob05c commented on issue #8519:
URL: https://github.com/apache/trafficserver/issues/8519#issuecomment-976078484


   The settings are in records.config: 
   
   https://docs.trafficserver.apache.org/en/8.1.x/admin-guide/files/records.config.en.html#parent-proxy-configuration
   
   There are a lot of variables here. 
   
   First, it will retry a parent `proxy.config.http.parent_proxy.fail_threshold` times before marking it down. Each time, the timeout will be `proxy.config.http.parent_proxy.connect_attempts_timeout`. The time before the attempt fails can be up to that time, such as if a firewall is simply dropping packets, but maybe be shorter, such as a firewall returning a TCP Reset. 
   
   If your `proxy.config.http.parent_proxy.total_connect_attempts` is less than `proxy.config.http.parent_proxy.fail_threshold`, the time to mark down will also depend on how long in-between client requests.
   
   After a parent is marked down, ATS will wait `proxy.config.http.parent_proxy.retry_time` before trying it again for a future client request.
   
   ATS will make `proxy.config.http.parent_proxy.per_parent_connect_attempts` to a single parent. Then it will try the next parent (per the parent selection algorithm - round_robin, strict, consistent hash). After making a total of `proxy.config.http.parent_proxy.total_connect_attempts` attempts, it will return an error to the client.
   
   So, the time to reinstate a downed parent after the initial attempt could be as much as `proxy.config.http.parent_proxy.fail_threshold * 
   (proxy.config.http.parent_proxy.connect_attempts_timeout + proxy.config.http.parent_proxy.retry_time) * "the time between clients requesting" + 
   proxy.config.http.parent_proxy.retry_time + 
   proxy.config.http.parent_proxy.connect_attempts_timeout`
   
   Or as little as `proxy.config.http.parent_proxy.fail_threshold`.
   
   Assuming my math is right. Again, there are a lot of variables in-flight here.
   
   This is also assuming you're using parent.config and have `proxy.config.http.parent_proxy_routing_enable` set to `1`. If you're not, the similar settings here will be used instead:
   
   https://docs.trafficserver.apache.org/en/8.1.x/admin-guide/files/records.config.en.html#origin-server-connect-attempts
   
   You might also find this helpful: 
   
   https://docs.trafficserver.apache.org/en/8.1.x/admin-guide/performance/index.en.html#timeout-settings
   


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