Shadow service manager should be idempotent

[kevinpollet]

Feature Request

Proposal

To forward traffic through mesh proxies, Maesh uses shadow services. To create, update or delete a shadow service corresponding to a user service the Maesh controller subscribes to service events emitted by informers.

However, it could be possible that the controller misses some events which can lead to bad state and behaviour. e.g. if the controller is down and a user service is deleted, on the next deployment, the shadow service is not created or updated which will not reflect potential changes.

To make sure that the shadow services state reflects the last known cluster state, the shadow service manager could be idempotent. Also, a service update event could create the corresponding shadow service if it does not exist to deal with missing create events.