update link-cost (#254)

* update link-cost

Author: pwright

cli/link-cost.adoc

@@ -1,3 +1,4 @@
+include::../partials/attributes.adoc[]
 // Type: procedure
 [id="specifying-link-cost"] 
 == Specifying link cost
@@ -79,4 +80,15 @@ You can view the traffic levels corresponding to each client.
 
 NOTE: If there are multiple clients on different sites, filter the view to each client to determine the effect of cost on traffic.
 For example, in a two site network linked with a high cost with servers and clients on both sites, you can see that a client is served by the local servers while a local server is available.
---
+--
+
+A common use-case for specifying cost is to provide automatic failover.
+As described in {single-link}, you might have two instances of a server with a high cost for the link to the backup server:
+
+* local server (effective cost = 0)
+* remote server (link cost = 99999)
+
+In this case, connections are always routed to the local server and fails over to the remote server when the local server becomes available.
+
+Some complex applications, especially stateful ones, require "orchestrated" failover, meaning you need control over the order in which traffic is redirected from one set of workloads to another. 
+{skupper-name} does not offer this type of orchestration, you need to implement that orchestration for those applications.

partials/attributes.adoc

@@ -17,6 +17,7 @@
 :kube-ref-link: https://skupper.io/docs/kubernetes-reference/index.html[Skupper Kubernetes CLI reference]
 :pod-ref-link: https://skupper.io/docs/kubernetes-reference/index.html[Skupper Podman CLI reference]
 :cost-link: ../cli/index.html#specifying-link-cost[Specifying link cost]
+:single-link: ../cli/index.html#deploying-single-logical-service[Deploying a single logical service]
 
 
 :skupper-operator-name: Skupper operator