I have already made a Kubernetes 1.5 cluster which is running in AWS using KOPS. I have many nodes in there with various instance type such as t2.medium, m3.medium, c4.large and c4.xlarge. But sometimes my Kubernetes pods running on t2.medium, m3.medium, c4.large cannot access external service like Amazon Relational Database Service (RDS), Elasticsearch and external SMS service. For RDS i got an error message PG::ConnectionBad and for others i got timeout. Does the problem come from AWS node instance or from Kubernetes pods? Because i never get an error if using c4.xlarge and up. If the problem come from my AWS instance, why that happened?

Thank you