Add Stronger Isolation Semantics for Routing Rules

[Peiyingy]

Proposal: Add Stronger Isolation Semantics for Routing Rules

Today, Trino-Gateway supports routing rules that can pin traffic to either a routing group. However, the current behavior still allows fallback routing when the pinned backend becomes unavailable.

At LinkedIn, we have some use cases where certain workloads must be strictly isolated from the general adhoc clusters. To support this, we propose introducing an optional enforceIsolation flag in routing-rule definitions.

• When enforceIsolation = false (default), the routing behavior remains unchanged.
• When enforceIsolation = true, the gateway would not fall back to adhoc clusters if the pinned backend becomes unavailable. Instead, the query should fail immediately at the gateway layer, ensuring true isolation.

Sample Routing Rule

---
name: "user_pinning_rule"
priority: 1
enforceIsolation: True
condition: "request.getHeader(\"X-Trino-User\") == \"user\""
actions:
  - "result.put(\"routingGroup\", \"Trino-1\")"