Load Balancing and Failover

Skupper V2 provides two mechanisms for controlling traffic distribution. The official docs recommend MultiKeyListener as the preferred approach.

Approach 1: MultiKeyListener (Preferred)

Per-service, explicit control. See MultiKeyListener.

• Weighted: Proportional distribution across routing keys
• Priority: Failover with preference order
• Per-service: Each service gets its own strategy
• Predictable: Not influenced by connection timing or link metrics

Approach 2: Link Cost (Alternative)

Global, implicit control via the cost field on Link resources.

apiVersion: skupper.io/v2alpha1
kind: Link
metadata:
  name: link-to-backup
spec:
  cost: 99999    # Very high = failover only

Link Cost Behavior

Rule	Detail
Default cost	1. Local workloads have implicit cost 0.
Multi-hop	Path cost = sum of all link costs along the path
Threshold behavior	Traffic flows on lowest-cost path until open connections exceed the cost of an alternative path, then spills over
Distribution	Statistical, not round robin
Scope	Applies to ALL services on a link — cannot be set per-service
Single path	When only one path exists, traffic flows regardless of cost
Failover	If a target becomes unavailable, traffic moves to remaining path regardless of cost

Failover via Link Cost

Set backup link cost very high:

• Local server: effective cost 0
• Remote backup: link cost 99999
• Result: All traffic goes local; failover to remote only when local is down

Limitations

• Cannot set different costs for different services on the same link
• No orchestrated failover for stateful applications
• Behavior depends on connection count thresholds

Comparison

Aspect	Link Cost	MultiKeyListener
Granularity	Per-link (global)	Per-service
Control	Implicit (threshold-based)	Explicit (weights/priority)
Predictability	Depends on connection count	Deterministic ratios
Configuration	On Link resource	On MultiKeyListener resource
Docs recommendation	“Alternative”	“Preferred”