Routing between Kubernetes cluster and Docker container in the VM - docker

Question

I have setup Kubernates cluster in the VM (Ubuntu 18.04.1 LTS) on the Azure cloud using preconfigured scripts.
MongoDB docker container is running along with K8s cluster. My aim is to connect MongoDB to CMS container which is running inside the K8s.
Docker containers:
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
3883f7b397cf mongo "docker-entrypoint.s…" 5 hours ago Up 5 hours 0.0.0.0:27017->27017/tcp mongodb
299239d90cbb mirantis/kubeadm-dind-cluster:v1.12 "/sbin/dind_init sys…" 27 hours ago Up 27 hours 8080/tcp kube-node-2
34c8bd5fad2e mirantis/kubeadm-dind-cluster:v1.12 "/sbin/dind_init sys…" 27 hours ago Up 27 hours 8080/tcp kube-node-1
15a2d6521e6e mirantis/kubeadm-dind-cluster:v1.12 "/sbin/dind_init sys…" 27 hours ago Up 27 hours 127.0.0.1:32768->8080/tcp kube-master
Kubernates nodes:
$ kubectl get services -o wide
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE SELECTOR
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 26h <none>
mycms LoadBalancer 10.97.53.114 <pending> 80:31664/TCP 18s app=mycms,tier=frontend
Kubernates service:
$ kubectl get services -o wide
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE SELECTOR
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 26h <none>
mycms LoadBalancer 10.97.53.114 <pending> 80:31664/TCP 112s app=mycms,tier=frontend
Kubernates pods:
$ kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE
mycms-dc4978ffc-khvj2 1/1 Running 0 4m8s 10.244.2.13 kube-node-1 <none>
MongoDB container's IP address is 172.17.0.2
Kubernates master container IP address is 10.192.0.2
Kubernates node 1 container IP address is 10.192.0.3
Kubernates node 2 container IP address is 10.192.0.4
As CMS pod is running on 10.244.2.13 which is inside the k8s container.
For testing, I have installed mongo-client on the host and test the connection which works well.
But CMS doesn't reach MongoDB container (I am passing Mongo String to pod in an environmental variable).
CMS pod's log
MongoError: failed to connect to server [172.17.0.2:27017] on first connect [MongoError: connect EHOSTUNREACH 172.17.0.2:27017]
How do I route MongoDB container and CMS container? Is anything wrong/missed in my approach?
Please let me know if you need further information. Thanks!

Answer 1

You need to use the IP address of the host where Docker is installed, not internal MongoDB container's IP address, to connect to MongoDB from the Kubernetes cluster or form any other host. According to the results of your docker ps -a, you have exposed 27017 port for MongoDB container, therefore <hostIP>:27017 should be used, not 172.17.0.2:27017.
By default in Kubernetes, there are no restrictions to connect outside the cluster.
Also, you may have firewall rules in Azure that forbid connections between hosts.