<p>I am running a cluster of</p>

<ul>
<li>3 services that hold a deployment for: Mongodb, Postgres, and a Rest-server</li>
<li>The Mongo and Postgres service as ClusterIP but the Rest-Server uses NodePort</li>
<li>When I <code>kubectl exec</code> and shell into the pods themselves, I can access Mongo/Postgres but using the docker network IP address</li>
<li>When I try to use the kubernetes service IP address (as given by the ClusterIP on Minikube) I can't get through</li>
</ul>

<p>Here is some sample commands that show the problem</p>

<p>Shell in:</p>

<pre><code>HOST$ kubectl exec -it my-system-mongo-54b8c75798-lptzq /bin/bash
</code></pre>

<p>Once in, I connect to mongo using the docker network IP:</p>

<pre><code>MONGO-POD# mongo mongodb://172.17.0.6
Welcome to the MongoDB shell.
&gt; exit
bye
</code></pre>

<p>Now I try to use the K8 service IP (the DNS works, as it gets translated to 10.96.154.36 as seen below)</p>

<pre><code>MONGO-POD# mongo mongodb://my-system-mongo
MongoDB shell version v3.6.3
connecting to: mongodb://my-system-mongo
2020-01-03T02:39:55.883+0000 W NETWORK  [thread1] Failed to connect to 10.96.154.36:27017 after 5000ms milliseconds, giving up.
2020-01-03T02:39:55.903+0000 E QUERY    [thread1] Error: couldn't connect to server my-system-mongo:27017, connection attempt failed :
connect@src/mongo/shell/mongo.js:251:13
@(connect):1:6
exception: connect failed
</code></pre>

<p>Ping also doesn't work</p>

<pre><code>MONGO-POD# ping my-system-mongo
PING my-system-mongo.default.svc.cluster.local (10.96.154.36) 56(84) bytes of data.
--- my-system-mongo.default.svc.cluster.local ping statistics ---
112 packets transmitted, 0 received, 100% packet loss, time 125365ms
</code></pre>

<p>My set up is running Minikube 1.6.2 with Kubernetes 1.17 and Helm 3.0.2. Here is my full (helm created) dry run yaml file:</p>

<pre><code>NAME: mysystem-1578018793
LAST DEPLOYED: Thu Jan  2 18:33:13 2020
NAMESPACE: default
STATUS: pending-install
REVISION: 1
HOOKS:
---
# Source: mysystem/templates/tests/test-connection.yaml
apiVersion: v1
kind: Pod
metadata:
  name: "my-system-test-connection"
  labels:
    helm.sh/chart: mysystem-0.1.0
    app.kubernetes.io/name: mysystem
    app.kubernetes.io/instance: mysystem-1578018793
    app.kubernetes.io/version: "1.16.0"
    app.kubernetes.io/managed-by: Helm
  annotations:
    "helm.sh/hook": test-success
spec:
  containers:
    - name: wget
      image: busybox
      command: ['wget']
      args:  ['my-system:']
  restartPolicy: Never
MANIFEST:
---
# Source: mysystem/templates/configmap.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: my-system-configmap
  labels:
    helm.sh/chart: mysystem-0.1.0
    app.kubernetes.io/name: mysystem
    app.kubernetes.io/instance: mysystem-1578018793
    app.kubernetes.io/version: "1.16.0"
    app.kubernetes.io/managed-by: Helm
data:
  _lots_of_key_value_pairs: here-I-shortened-it
---
# Source: mysystem/templates/my-system-mongo-service.yaml
apiVersion: v1
kind: Service
metadata:
  name: my-system-mongo
  labels:
    helm.sh/chart: mysystem-0.1.0
    app.kubernetes.io/name: mysystem
    app.kubernetes.io/instance: mysystem-1578018793
    app.kubernetes.io/version: "1.16.0"
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/component: mongo
spec:
  type: ClusterIP
  ports:
  - port: 27017
    targetPort: 27017
    protocol: TCP
    name: mongo
  selector:
    app.kubernetes.io/name: mysystem
    app.kubernetes.io/instance: mysystem-1578018793
    app.kubernetes.io/component: mongo
---
# Source: mysystem/templates/my-system-pg-service.yaml
apiVersion: v1
kind: Service
metadata:
  name: my-system-postgres
  labels:
    helm.sh/chart: mysystem-0.1.0
    app.kubernetes.io/name: mysystem
    app.kubernetes.io/instance: mysystem-1578018793
    app.kubernetes.io/version: "1.16.0"
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/component: postgres
spec:
  type: ClusterIP
  ports:
  - port: 5432
    targetPort: 5432
    protocol: TCP
    name: postgres
  selector:
    app.kubernetes.io/name: mysystem
    app.kubernetes.io/instance: mysystem-1578018793
    app.kubernetes.io/component: postgres
---
# Source: mysystem/templates/my-system-restsrv-service.yaml
apiVersion: v1
kind: Service
metadata:
  name: my-system-rest-server
  labels:
    helm.sh/chart: mysystem-0.1.0
    app.kubernetes.io/name: mysystem
    app.kubernetes.io/instance: mysystem-1578018793
    app.kubernetes.io/version: "1.16.0"
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/component: rest-server
spec:
  type: NodePort
  ports:
  #- port: 8009
  #  targetPort: 8009
  #  protocol: TCP
  #  name: jpda
  - port: 8080
    targetPort: 8080
    protocol: TCP
    name: http
  selector:
    app.kubernetes.io/name: mysystem
    app.kubernetes.io/instance: mysystem-1578018793
    app.kubernetes.io/component: rest-server
---
# Source: mysystem/templates/my-system-mongo-deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-system-mongo
  labels:
    helm.sh/chart: mysystem-0.1.0
    app.kubernetes.io/name: mysystem
    app.kubernetes.io/instance: mysystem-1578018793
    app.kubernetes.io/version: "1.16.0"
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/component: mongo
spec:
  replicas: 1
  selector:
    matchLabels:
      app.kubernetes.io/name: mysystem
      app.kubernetes.io/instance: mysystem-1578018793
      app.kubernetes.io/component: mongo
  template:
    metadata:
      labels:
        app.kubernetes.io/name: mysystem
        app.kubernetes.io/instance: mysystem-1578018793
        app.kubernetes.io/component: mongo
    spec:
      imagePullSecrets:
        - name: regcred
      serviceAccountName: default
      securityContext:
        {}
      containers:
      - name: my-system-mongo-pod
        securityContext:
            {}
        image: private.hub.net/my-system-mongo:latest
        imagePullPolicy: Always
        envFrom:
          - configMapRef:
              name: my-system-configmap
        ports:
        - name: "mongo"
          containerPort: 27017
          protocol: TCP
        resources:
            {}
---
# Source: mysystem/templates/my-system-pg-deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-system-postgres
  labels:
    helm.sh/chart: mysystem-0.1.0
    app.kubernetes.io/name: mysystem
    app.kubernetes.io/instance: mysystem-1578018793
    app.kubernetes.io/version: "1.16.0"
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/component: postgres
spec:
  replicas: 1
  selector:
    matchLabels:
      app.kubernetes.io/name: mysystem
      app.kubernetes.io/instance: mysystem-1578018793
      app.kubernetes.io/component: postgres
  template:
    metadata:
      labels:
        app.kubernetes.io/name: mysystem
        app.kubernetes.io/instance: mysystem-1578018793
        app.kubernetes.io/component: postgres
    spec:
      imagePullSecrets:
        - name: regcred
      serviceAccountName: default
      securityContext:
        {}
      containers:
      - name: mysystem
        securityContext:
            {}
        image: private.hub.net/my-system-pg:latest
        imagePullPolicy: Always
        envFrom:
          - configMapRef:
              name: my-system-configmap
        ports:
        - name: postgres
          containerPort: 5432
          protocol: TCP
        resources:
            {}
---
# Source: mysystem/templates/my-system-restsrv-deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-system-rest-server
  labels:
    helm.sh/chart: mysystem-0.1.0
    app.kubernetes.io/name: mysystem
    app.kubernetes.io/instance: mysystem-1578018793
    app.kubernetes.io/version: "1.16.0"
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/component: rest-server
spec:
  replicas: 1
  selector:
    matchLabels:
      app.kubernetes.io/name: mysystem
      app.kubernetes.io/instance: mysystem-1578018793
      app.kubernetes.io/component: rest-server
  template:
    metadata:
      labels:
        app.kubernetes.io/name: mysystem
        app.kubernetes.io/instance: mysystem-1578018793
        app.kubernetes.io/component: rest-server
    spec:
      imagePullSecrets:
        - name: regcred
      serviceAccountName: default
      securityContext:
        {}
      containers:
      - name: mysystem
        securityContext:
            {}
        image: private.hub.net/my-system-restsrv:latest
        imagePullPolicy: Always
        envFrom:
          - configMapRef:
              name: my-system-configmap
        ports:
        - name: rest-server
          containerPort: 8080
          protocol: TCP
        #- name: "jpda"
        #  containerPort: 8009
        #  protocol: TCP
        resources:
            {}

NOTES:
1. Get the application URL by running these commands:
  export POD_NAME=$(kubectl get pods --namespace default -l "app.kubernetes.io/name=mysystem,app.kubernetes.io/instance=mysystem-1578018793" -o jsonpath="{.items[0].metadata.name}")
  echo "Visit http://127.0.0.1:8080 to use your application"
  kubectl --namespace default port-forward $POD_NAME 8080:80
</code></pre>

<p>My best theory (in part after <a href="https://kubernetes.io/docs/tasks/debug-application-cluster/debug-service/#does-the-service-work-by-dns" rel="nofollow noreferrer">working through this</a>) is that the <code>kube-proxy</code> is not working properly in minikube, however I am not sure how to troubleshoot this. When is shell into minikube and grep through journalctl for proxy I get this:</p>

<pre><code># grep proxy journal.log
Jan 03 02:16:02 minikube sudo[2780]:   docker : TTY=unknown ; PWD=/home/docker ; USER=root ; COMMAND=/bin/touch -d 2020-01-02 18:16:03.05808666 -0800 /var/lib/minikube/certs/proxy-client.crt
Jan 03 02:16:02 minikube sudo[2784]:   docker : TTY=unknown ; PWD=/home/docker ; USER=root ; COMMAND=/bin/touch -d 2020-01-02 18:16:03.05908666 -0800 /var/lib/minikube/certs/proxy-client.key
Jan 03 02:16:15 minikube kubelet[2821]: E0103 02:16:15.423027    2821 reflector.go:156] object-"kube-system"/"kube-proxy": Failed to list *v1.ConfigMap: configmaps "kube-proxy" is forbidden: User "system:node:minikube" cannot list resource "configmaps" in API group "" in the namespace "kube-system": no relationship found between node "minikube" and this object
Jan 03 02:16:15 minikube kubelet[2821]: I0103 02:16:15.503466    2821 reconciler.go:209] operationExecutor.VerifyControllerAttachedVolume started for volume "kube-proxy-token-n78g9" (UniqueName: "kubernetes.io/secret/50fbf70b-724a-4b76-af7f-5f4b91735c84-kube-proxy-token-n78g9") pod "kube-proxy-pbs6s" (UID: "50fbf70b-724a-4b76-af7f-5f4b91735c84")
Jan 03 02:16:15 minikube kubelet[2821]: I0103 02:16:15.503965    2821 reconciler.go:209] operationExecutor.VerifyControllerAttachedVolume started for volume "xtables-lock" (UniqueName: "kubernetes.io/host-path/50fbf70b-724a-4b76-af7f-5f4b91735c84-xtables-lock") pod "kube-proxy-pbs6s" (UID: "50fbf70b-724a-4b76-af7f-5f4b91735c84")
Jan 03 02:16:15 minikube kubelet[2821]: I0103 02:16:15.530948    2821 reconciler.go:209] operationExecutor.VerifyControllerAttachedVolume started for volume "lib-modules" (UniqueName: "kubernetes.io/host-path/50fbf70b-724a-4b76-af7f-5f4b91735c84-lib-modules") pod "kube-proxy-pbs6s" (UID: "50fbf70b-724a-4b76-af7f-5f4b91735c84")
Jan 03 02:16:15 minikube kubelet[2821]: I0103 02:16:15.538938    2821 reconciler.go:209] operationExecutor.VerifyControllerAttachedVolume started for volume "kube-proxy" (UniqueName: "kubernetes.io/configmap/50fbf70b-724a-4b76-af7f-5f4b91735c84-kube-proxy") pod "kube-proxy-pbs6s" (UID: "50fbf70b-724a-4b76-af7f-5f4b91735c84")
Jan 03 02:16:15 minikube systemd[1]: Started Kubernetes transient mount for /var/lib/kubelet/pods/50fbf70b-724a-4b76-af7f-5f4b91735c84/volumes/kubernetes.io~secret/kube-proxy-token-n78g9.
Jan 03 02:16:16 minikube kubelet[2821]: E0103 02:16:16.670527    2821 configmap.go:200] Couldn't get configMap kube-system/kube-proxy: failed to sync configmap cache: timed out waiting for the condition
Jan 03 02:16:16 minikube kubelet[2821]: E0103 02:16:16.670670    2821 nestedpendingoperations.go:270] Operation for "\"kubernetes.io/configmap/50fbf70b-724a-4b76-af7f-5f4b91735c84-kube-proxy\" (\"50fbf70b-724a-4b76-af7f-5f4b91735c84\")" failed. No retries permitted until 2020-01-03 02:16:17.170632812 +0000 UTC m=+13.192986021 (durationBeforeRetry 500ms). Error: "MountVolume.SetUp failed for volume \"kube-proxy\" (UniqueName: \"kubernetes.io/configmap/50fbf70b-724a-4b76-af7f-5f4b91735c84-kube-proxy\") pod \"kube-proxy-pbs6s\" (UID: \"50fbf70b-724a-4b76-af7f-5f4b91735c84\") : failed to sync configmap cache: timed out waiting for the condition"
</code></pre>

<p>And while that does show some problems, I am not sure how to act on them or correct it.</p>

<p>UPDATE: </p>

<p>I spotted this when grepping through the journal:</p>

<pre><code># grep conntrack journal.log
Jan 03 02:16:04 minikube kubelet[2821]: W0103 02:16:04.286682    2821 hostport_manager.go:69] The binary conntrack is not installed, this can cause failures in network connection cleanup.
</code></pre>

<p>Looking into conntrack, though the minikube VM doesn't have yum or apt!</p>

E.S.
<p>Let's look at the relevant Service:</p>

<pre class="lang-yaml prettyprint-override"><code>apiVersion: v1
kind: Service
metadata:
  name: my-system-mongo
spec:
  ports:
  - port: 27017       # note typo here, see @aviator's answer
    targetPort: 27017
    protocol: TCP
    name: mongo
  selector:
    app.kubernetes.io/name: mysystem
    app.kubernetes.io/instance: mysystem-1578018793
</code></pre>

<p>In particular note the <code>selector:</code>; this can route traffic to any pod that has these two labels.  For example, this is a valid target:</p>

<pre class="lang-yaml prettyprint-override"><code>apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-system-postgres
spec:
  selector:
    matchLabels:
      app.kubernetes.io/name: mysystem
      app.kubernetes.io/instance: mysystem-1578018793
  template:
    metadata:
      labels:
        app.kubernetes.io/name: mysystem
        app.kubernetes.io/instance: mysystem-1578018793
</code></pre>

<p>Since every pod has the same pair of labels, any service can send traffic to any pod; your "MongoDB" service isn't necessarily targeting the actual MongoDB pod.  Your deployment specs have the same problem and I wouldn't be surprised if the <code>kubectl get pods</code> output is a little bit confused.</p>

<p>The right answer here is to add another label that distinguishes the different parts of your application from each other.  <a href="https://helm.sh/docs/topics/chart_best_practices/labels/" rel="nofollow noreferrer">The Helm docs</a> recommend</p>

<pre class="lang-yaml prettyprint-override"><code>app.kubernetes.io/component: mongodb
</code></pre>

<p>This must appear in the labels of the pod spec embedded in the deployments, the matching deployment selector, and the matching service selector; simply setting it on all related objects including the deployment and service labels makes sense.</p>
