NE-822 Don't scale route weight on single service routes #377
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/hold I think we should wait for perf&scale test. |
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pkg/router/template/router.go
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| for key := range serviceUnits { | ||
| serviceUnitNames[key] = 1 | ||
| } |
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What if the service unit has 0 endpoints? We should check for that case:
| for key := range serviceUnits { | |
| serviceUnitNames[key] = 1 | |
| } | |
| for key := range serviceUnits { | |
| if r.numberOfEndpoints(key) > 0 { | |
| serviceUnitNames[key] = 1 | |
| } | |
| } |
Granted, omitting the r.numberOfEndpoints(key) > 0 check might not change the ultimate result from the config template:
{{- range $serviceUnitName, $weight := $cfg.ServiceUnitNames }}
{{- if ge $weight 0 }}{{/* weight=0 is reasonable to keep existing connections to backends with cookies as we can see the HTTP headers */}}
{{- with $serviceUnit := index $.ServiceUnits $serviceUnitName }}
{{- range $idx, $endpoint := processEndpointsForAlias $cfg $serviceUnit (env "ROUTER_BACKEND_PROCESS_ENDPOINTS" "") }}
{{/* [actual HAProxy config stuff here] */}}
{{- end }}{{/* end range processEndpointsForAlias */}}
{{- end }}{{/* end get serviceUnit from its name */}}
{{- end }}{{/* end range over serviceUnitNames */}}
In the template, the effect is the same whether range $serviceUnitName, $weight := $cfg.ServiceUnitNames iterates 0 times or whether range $idx, $endpoint := processEndpointsForAlias $cfg $serviceUnit (env "ROUTER_BACKEND_PROCESS_ENDPOINTS" "") iterates 0 times. However, it could cause problems for the dynamic config manager, which has logic like this:
// As the endpoints have changed, recalculate the weights.
newWeights := r.calculateServiceWeights(cfg.ServiceUnits)
// Get the weight for this service unit.
weight, ok := newWeights[id]
if !ok {
weight = 0
}Anyway, from a strict correctness perspective, I believe calculateServiceWeights needs the r.numberOfEndpoints(key) > 0 check.
Please add a unit test case to ensure we don't regress:
--- a/pkg/router/template/router_test.go
+++ b/pkg/router/template/router_test.go
@@ -873,6 +873,16 @@ func TestCalculateServiceWeights(t *testing.T) {
serviceWeights map[ServiceUnitKey]int32
expectedWeights map[ServiceUnitKey]int32
}{
+ {
+ name: "service with no endpoint",
+ serviceUnits: map[ServiceUnitKey][]Endpoint{
+ suKey1: {},
+ },
+ serviceWeights: map[ServiceUnitKey]int32{
+ suKey1: 100,
+ },
+ expectedWeights: map[ServiceUnitKey]int32{},
+ },
{
name: "equally weighted services with same number of endpoints",
serviceUnits: map[ServiceUnitKey][]Endpoint{There was a problem hiding this comment.
Good point, didn't think about a single service with no endpoints and exposing that datapath. Agreed it doesn't functionally changing anything, but keep our code clean for the future.
Done.
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/lgtm |
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Change to not scale weight to 256 if there is only one service for the route. More information can be found here: NE-709 Impact of Server Weight on Memory Allocation
In a nutshell, scaling the weight to 256 is redundant for single services routes since all servers in the haproxy backend will always have the same weight, so therefore weight 1 == weight 256. Reducing the weight helps with reducing the static memory allocation.