Always include one non-local target during discovery

henryr · henryr · commit a774206406b4 · 2025-01-16T12:02:16.000Z
Signed-off-by: Henry Robinson &lt;hrobinson@slack-corp.com&gt;
diff --git a/go/vt/vtgateproxy/discovery.go b/go/vt/vtgateproxy/discovery.go
@@ -323,7 +323,9 @@ func (b *JSONGateResolverBuilder) parse() (bool, error) {
 	for poolType := range targets {
 		b.sorter.shuffleSort(targets[poolType], b.affinityField, b.affinityValue)
 		if len(targets[poolType]) > *numConnections {
-			targets[poolType] = targets[poolType][:b.numConnections]
+			// Always grab one non-local target to protect against a complete local failure.
+			nonLocal := targets[poolType][len(targets[poolType])-1]
+			targets[poolType] = append(targets[poolType][:b.numConnections], nonLocal)
 		}
 		targetCount.Set(poolType, int64(len(targets[poolType])))
 	}

Original file line number	Diff line number	Diff line change
`@@ -323,7 +323,9 @@ func (b *JSONGateResolverBuilder) parse() (bool, error) {`
`323`	`323`	`for poolType := range targets {`
`324`	`324`	`b.sorter.shuffleSort(targets[poolType], b.affinityField, b.affinityValue)`
`325`	`325`	`if len(targets[poolType]) > *numConnections {`
`326`		`- targets[poolType] = targets[poolType][:b.numConnections]`
	`326`	`+ // Always grab one non-local target to protect against a complete local failure.`
	`327`	`+ nonLocal := targets[poolType][len(targets[poolType])-1]`
	`328`	`+ targets[poolType] = append(targets[poolType][:b.numConnections], nonLocal)`
`327`	`329`	`}`
`328`	`330`	`targetCount.Set(poolType, int64(len(targets[poolType])))`
`329`	`331`	`}`