Can't connect to MariaDB by hostname within a Kubernetes cluster

If I set up MariaDB form the official image within a Docker Compose configuration, I can access it by its host name - for example if in a bash shell within the MariaDB container:

# host db
db has address 172.21.0.2


# curl telnet://db:3306
Warning: Binary output can mess up your terminal. Use "--output -" to tell 
Warning: curl to output it to your terminal anyway, or consider "--output 
Warning: <FILE>" to save to a file.

• no connection refused issue here

But if have MariaDB deployed from the official image within a Kubernetes cluster (tried both MicroK8s and GKE), I can connect to it via localhost but not by its host name:

# host db
db.my-namspace.svc.cluster.local has address 10.152.183.124

# curl telnet://db:3306
curl: (7) Failed to connect to db port 3306: Connection refused

# curl telnet://localhost:3306
Warning: Binary output can mess up your terminal. Use "--output -" to tell 
Warning: curl to output it to your terminal anyway, or consider "--output 
Warning: <FILE>" to save to a file.

• connection is refused for the service host name, but localhost responds

I've tried to replace the included my.cnf with a simplified version like:

[mysqld]
skip-grant-tables
skip-networking=0
#### Unix socket settings (making localhost work)
user            = mysql
pid-file        = /var/run/mysqld/mysqld.pid
socket          = /var/run/mysqld/mysqld.sock

#### TCP Socket settings (making all remote logins work)
port         = 3306
bind-address = *

• with no luck

The MariaDB Kubernetes deployment is like:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: db
spec:
  replicas: 1
  strategy:
    type: Recreate
  selector:
    matchLabels:
      name: db
  template:
    metadata:
      labels:
        name: db
    spec:
      containers:
      - env:
        - name: MYSQL_PASSWORD
          value: template
        - name: MYSQL_ROOT_PASSWORD
          value: root
        - name: MYSQL_USER
          value: template
        image: mariadb:10.4
        name: db
        ports:
        - containerPort: 3306
        resources: {}
        volumeMounts:
        - mountPath: /var/lib/mysql
          name: dbdata
      restartPolicy: Always
      volumes:
      - name: dbdata
        persistentVolumeClaim:
          claimName: dbdata
status: {}

and the corresponding Persistent Volume Claim:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  labels:
    io.kompose.service: dbdata
  name: dbdata
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 100Mi
status: {}

It baffles me that the same configuration works with Docker Compose but not within a Kubernetes cluster.

Any ideas what may be going on?

Update 2020-03-18 I forgot to include the service declaration for the database and add it here:

apiVersion: v1
kind: Service
metadata:
  labels:
    app: db
  name: db
spec:
  ports:
  - name: "3306"
    port: 3306
    targetPort: 3306
  selector:
    app: db
    name: db
  type: ClusterIP
status:
  loadBalancer: {}

...am including both app and name for the spec.selector - am used to having only name but @Al-waleed Shihadeh's example includes app so I'll include that also, just in case - but without success.

Here are outputs from a couple of kubectl listing commands:

$ sudo microk8s.kubectl get svc db -n my-namespace
NAME   TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)    AGE
db     ClusterIP   10.152.183.246   <none>        3306/TCP   35m

$ sudo microk8s.kubectl get pods -owide -n my-namespace
NAME                           READY   STATUS             RESTARTS   AGE   IP            NODE          NOMINATED NODE   READINESS GATES
db-77cbcf87b6-l44lm            1/1     Running            0          34m   10.1.48.118   microk8s-vm   <none>           <none>

Solution Comparing the service declaration posted by KoopaKiller, which proved to work, I finally noticed that setting the protocol attribute to "TCP" in the ports declaration was missing - this part:

spec:
  ports:
  - protocol: TCP
...