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health check: overriding health threshold for edge intervals #3174

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Apr 30, 2018
Merged

health check: overriding health threshold for edge intervals #3174

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d7b288b
health check: overriding health threshold for edge intervals
juchem Apr 20, 2018
5b08ace
fixing implementation to follow HAProxy's behavior
juchem Apr 20, 2018
90b3e33
improving comments formatting in tests
juchem Apr 26, 2018
7b34697
further documentation on the edge interval behavior
juchem Apr 30, 2018
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16 changes: 15 additions & 1 deletion include/envoy/upstream/health_checker.h
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,21 @@ namespace Upstream {

enum class HealthState { Unhealthy, Healthy };

enum class HealthTransition { Unchanged, Changed };
enum class HealthTransition {
/**
* Used when the health state of a host hasn't changed.
*/
Unchanged,
/**
* Used when the health state of a host has changed.
*/
Changed,
/**
* Used when the health check result differs from the health state of a host, but a change to the
* latter is delayed due to healthy/unhealthy threshold settings.
*/
ChangePending
};

/**
* Wraps active health checking of an upstream cluster.
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23 changes: 19 additions & 4 deletions source/common/upstream/health_checker_base_impl.cc
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Expand Up @@ -57,14 +57,25 @@ std::chrono::milliseconds HealthCheckerImplBase::interval(HealthState state,
// refer to the HealthCheck API documentation for more details.
uint64_t base_time_ms;
if (cluster_.info()->stats().upstream_cx_total_.used()) {
// When healthy/unhealthy threshold is configured the health transition of a host will be
// delayed. In this situation Envoy should use the edge interval settings between health checks.
//
// Example scenario for an unhealthy host with healthy_threshold set to 3:
// - check fails, host is still unhealthy and next check happens after unhealthy_interval;
// - check succeeds, host is still unhealthy and next check happens after healthy_edge_interval;
// - check succeeds, host is still unhealthy and next check happens after healthy_edge_interval;
// - check succeeds, host is now healthy and next check happens after interval;
// - check succeeds, host is still healthy and next check happens after interval.
switch (state) {
case HealthState::Unhealthy:
base_time_ms = changed_state == HealthTransition::Changed ? unhealthy_edge_interval_.count()
: unhealthy_interval_.count();
base_time_ms = changed_state == HealthTransition::ChangePending
? unhealthy_edge_interval_.count()
: unhealthy_interval_.count();
break;
default:
base_time_ms = changed_state == HealthTransition::Changed ? healthy_edge_interval_.count()
: interval_.count();
base_time_ms = changed_state == HealthTransition::ChangePending
? healthy_edge_interval_.count()
: interval_.count();
break;
}
} else {
Expand Down Expand Up @@ -189,6 +200,8 @@ void HealthCheckerImplBase::ActiveHealthCheckSession::handleSuccess() {
host_->healthFlagClear(Host::HealthFlag::FAILED_ACTIVE_HC);
parent_.incHealthy();
changed_state = HealthTransition::Changed;
} else {
changed_state = HealthTransition::ChangePending;
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I specifically wanted to respect the former semantics of changed_state, when it was a boolean.

Changed is only set where before changed_state would be set to true. Given that all places that used to check for truth-ness of changed_state have been changed to changed_state == HealthTransition::Changed in a previous PR, truth-ness checks still hold:

envoy-dev@envoy-dev:~/src/envoy$ egrep -R '(== HealthTransition::Changed)' . 2>/dev/null
./source/common/upstream/upstream_impl.cc:        if (changed_state == HealthTransition::Changed) {
./source/common/upstream/health_checker_base_impl.cc:      base_time_ms = (changed_state == HealthTransition::Changed ||
./source/common/upstream/health_checker_base_impl.cc:      base_time_ms = (changed_state == HealthTransition::Changed ||
./source/common/upstream/cluster_manager_impl.cc:          if (changed_state == HealthTransition::Changed &&

Where changed_state would have been false, it's now either ChangePending or Unchanged. Therefore new state would only affect false-ness checks. Since there are no such checks, the addition of the new state shouldn't be a problem:

envoy-dev@envoy-dev:~/src/envoy$ egrep -R '(!= HealthTransition::Changed|== HealthTransition::Unchanged)' . 2>/dev/null
envoy-dev@envoy-dev:~/src/envoy$

With the above in mind, the semantics should still hold.

}
}

Expand All @@ -210,6 +223,8 @@ HealthTransition HealthCheckerImplBase::ActiveHealthCheckSession::setUnhealthy(F
host_->healthFlagSet(Host::HealthFlag::FAILED_ACTIVE_HC);
parent_.decHealthy();
changed_state = HealthTransition::Changed;
} else {
changed_state = HealthTransition::ChangePending;
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same reasoning as above

}
}

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3 changes: 3 additions & 0 deletions source/common/upstream/health_checker_impl.cc
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Expand Up @@ -610,6 +610,9 @@ std::ostream& operator<<(std::ostream& out, HealthTransition changed_state) {
case HealthTransition::Changed:
out << "Changed";
break;
case HealthTransition::ChangePending:
out << "ChangePending";
break;
}
return out;
}
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