Deployment has not matched the expected number of replicas.
Kubernetes Deployment resource does not have number of replicas which were declared to be in operation. For example deployment is expected to have 3 replicas, but it has less than that for a noticeable period of time.
In rare occasions there may be more replicas than it should and system did not clean it up.
Service degradation or unavailability.
- Check deployment status via
kubectl -n $NAMESPACE describe deployment $NAME.
- Check how many replicas are there declared.
- Check the status of the pods which belong to the replica sets under the deployment.
- Check pod template parameters such as:
- pod priority - maybe it was evicted by other more important pods
- resources - maybe it tries to use unavailable resource, such as GPU but there is limited number of nodes with GPU
- affinity rules - maybe due to affinities and not enough nodes it is not possible to schedule pods
- pod termination grace period - if too long then pods may be for too long in terminating state
- Check if Horizontal Pod Autoscaler (HPA) is not triggered due to untested values (requests values).
- Check if cluster-autoscaler is able to create new nodes - see its logs or cluster-autoscaler status configmap.
Depending on the conditions usually adding new nodes solves the issue.
Otherwise probably deployment or HPA definition needs to be fixed.
See Debugging Pods