This fixes state machine looping when using upstream connection throttling with parent selection#5674
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jrushford merged 1 commit intoapache:masterfrom Jun 25, 2019
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a parent proxy exceeds proxy.config.http.per_server.connection.max a state machine loop will occur when using parent selection to select a parent for redundancy and/or load balancing. The parent selection handling in the state machine did not handle the where the number of connections to a parent is exceeds when using throttling by setting proxy.config.http.per_server.connection.max. This will lead to state machine looping and a crash when the stack is overflowed due to the looping. Now this is handled by either trying a new uncongested origin or sending a negative 503 response if all available origins are congested.
vmamidi
approved these changes
Jun 25, 2019
| } else if (s->method == HTTP_WKSIDX_CONNECT && s->http_config_param->disable_ssl_parenting) { | ||
| s->parent_params->findParent(&s->request_data, &s->parent_result, s->txn_conf->parent_fail_threshold, | ||
| s->txn_conf->parent_retry_time); | ||
| if (s->parent_result.result == PARENT_SPECIFIED) { |
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Presumably this is initialized to a reasonable value, so the this check is valid despite possibly having to update the value in the else class? I wonder if findParent should just check its second argument and do the right thing in that case. Would it be too challenging to keep s->parent_result.result correct? Although it seems you already have that problem here.
SolidWallOfCode
approved these changes
Jun 25, 2019
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Fixes #5642 when using upstream connection throttling with parent selection.
Parent Selection may be used to provide redundancy and load balancing to origin servers. If upstream connection throttling is used on these origins, a state machine loop can occur that leads to a crash as the parent selection handlers did not handle this congestion connection throttling. This patch adds congestion connection throttling to the HttpSM parent handler,handle_response_from_parent().