A service by AWS that routes traffic based on simple logic
You can use AWS APP MESH to route traffic between OSM and GDM. First, all traffic will be sent to OSM using App Mesh's VirtualRouter.
VirtualRouter is an object to route traffic between K8S services. One service will be pointed to the ECS hosted OSM. Another service will be pointed to GDM using External Service
You can use a Cronjob which will run in a pod and sense timeout-related metrics from ElasticCache. If the condition matched - the code host in the pod and running as a CronJob will modify VirtualRouter.