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Move to single-flight for back-end queries

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When querying for replicas during a scale up event, then the
gateway can overwhelm the provider with requests. This is
especially true under high concurrent load.

The changes in this PR limit the inflight requests.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alex@openfaas.com>
This commit is contained in:
Alex Ellis (OpenFaaS Ltd)
2022-06-22 17:48:33 +01:00
committed by Alex Ellis
parent 8f8a93d43f
commit 6ed0ab71fb
3 changed files with 138 additions and 15 deletions
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57
gateway/scaling/function_scaler.go
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@ -10,15 +10,17 @@ import (
// ScalingConfig
func NewFunctionScaler(config ScalingConfig, functionCacher FunctionCacher) FunctionScaler {
return FunctionScaler{
Cache: functionCacher,
Config: config,
Cache: functionCacher,
Config: config,
SingleFlight: NewSingleFlight(),
}
}
// FunctionScaler scales from zero
type FunctionScaler struct {
Cache FunctionCacher
Config ScalingConfig
Cache FunctionCacher
Config ScalingConfig
SingleFlight *SingleFlight
}
// FunctionScaleResult holds the result of scaling from zero
@ -43,8 +45,11 @@ func (f *FunctionScaler) Scale(functionName, namespace string) FunctionScaleResu
Duration: time.Since(start),
}
}
getKey := fmt.Sprintf("GetReplicas-%s.%s", functionName, namespace)
queryResponse, err := f.Config.ServiceQuery.GetReplicas(functionName, namespace)
res, err := f.SingleFlight.Do(getKey, func() (interface{}, error) {
return f.Config.ServiceQuery.GetReplicas(functionName, namespace)
})
if err != nil {
return FunctionScaleResult{
@ -54,6 +59,16 @@ func (f *FunctionScaler) Scale(functionName, namespace string) FunctionScaleResu
Duration: time.Since(start),
}
}
if res == nil {
return FunctionScaleResult{
Error: fmt.Errorf("empty response from server"),
Available: false,
Found: false,
Duration: time.Since(start),
}
}
queryResponse := res.(ServiceQueryResponse)
f.Cache.Set(functionName, namespace, queryResponse)
@ -64,21 +79,35 @@ func (f *FunctionScaler) Scale(functionName, namespace string) FunctionScaleResu
}
scaleResult := backoff(func(attempt int) error {
queryResponse, err := f.Config.ServiceQuery.GetReplicas(functionName, namespace)
res, err := f.SingleFlight.Do(getKey, func() (interface{}, error) {
return f.Config.ServiceQuery.GetReplicas(functionName, namespace)
})
if err != nil {
return err
}
queryResponse = res.(ServiceQueryResponse)
f.Cache.Set(functionName, namespace, queryResponse)
if queryResponse.Replicas > 0 {
return nil
}
log.Printf("[Scale %d] function=%s 0 => %d requested", attempt, functionName, minReplicas)
setScaleErr := f.Config.ServiceQuery.SetReplicas(functionName, namespace, minReplicas)
if setScaleErr != nil {
return fmt.Errorf("unable to scale function [%s], err: %s", functionName, setScaleErr)
setKey := fmt.Sprintf("SetReplicas-%s.%s", functionName, namespace)
if _, err := f.SingleFlight.Do(setKey, func() (interface{}, error) {
log.Printf("[Scale %d] function=%s 0 => %d requested", attempt, functionName, minReplicas)
if err := f.Config.ServiceQuery.SetReplicas(functionName, namespace, minReplicas); err != nil {
return nil, fmt.Errorf("unable to scale function [%s], err: %s", functionName, err)
}
return nil, nil
}); err != nil {
return err
}
return nil
@ -95,10 +124,16 @@ func (f *FunctionScaler) Scale(functionName, namespace string) FunctionScaleResu
}
for i := 0; i < int(f.Config.MaxPollCount); i++ {
queryResponse, err := f.Config.ServiceQuery.GetReplicas(functionName, namespace)
res, err := f.SingleFlight.Do(getKey, func() (interface{}, error) {
return f.Config.ServiceQuery.GetReplicas(functionName, namespace)
})
queryResponse := res.(ServiceQueryResponse)
if err == nil {
f.Cache.Set(functionName, namespace, queryResponse)
}
totalTime := time.Since(start)
if err != nil {