RFC for configurable registration TTL

designs/configurable-registeration-ttl.md

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+# RFC: Configurable registeration TTL
+
+## Motivation
+
+[Issue](https://github.com/kubernetes-sigs/karpenter/issues/357)
+
+Karpenter currently hardcodes [registeration TTL](https://github.com/kubernetes-sigs/karpenter/blob/main/pkg/controllers/nodeclaim/lifecycle/liveness.go#L39) which means nodes must take < 15 minutes to come up and register with the Kubernetes control plane.
+
+This is problematic because some users have nodes that take longer that time to register. As mentioned in the issue, nodes that run GPU can often take > 15 minutes to start up. 
+
+## Introduce a configuration registeration TTL to NodeClass
+
+We will keep a default for all nodes at 15 minute TTL however in the cases that the NodeClass would be used with GPUs or known to take a longer time to register, we will expose a new configuration registerationTTL.
+
+```yaml
+spec:
+  registerationTTL:  30m
+```
+
+Evaluation conditions - 
+
+1. When evaluating liveness, check if NodeClass ref of NodeClaim contains a registerationTTL
+2. If it does, use that TTL instead of the default 15 minutes to evaluate if registeration TTL has been breached