Connect to mongodb with mongoose both in kubernetes

Your tasksdb Service exposes port 6004, not 27017. Try using the following URL:

const connection = "mongodb://tasksdb.default.svc.cluster.local:6004/tasks";

Changing your network depends on what networking CNI plugin you are using. Every plugin has different steps . For Calico please see https://docs.projectcalico.org/networking/migrate-pools

I believe this is your cluster ip setting for mongodb instance:

apiVersion: v1    kind: Service    metadata:      annotations:        kompose.cmd: kompose convert -f docker-compose.yml -o k8manifest.yml        kompose.version: 1.22.0 (955b78124)      creationTimestamp: null      labels:        io.kompose.service: tasksdb      name: tasksdb    spec:      ports:        - name: "6004"          port: 6004          targetPort: 27017      selector:        io.kompose.service: tasksdb    status:      loadBalancer: {}

When you create an instance of mongodb inside kubernetes, it runs inside a pod. To connect to a pod, we have to go through the cluster IP service. Anytime we are trying to connect to a cluster IP service we are going to write the name of that cluster iP service for the domain of connection url. in this case you connection url must be

mongodb://tasksdb:6004/nameOfDatabase