Connection issue between services in kubernetes - docker

Question

I have three different images related to my application which works fine in docker-compose and has issues running on kubernetes cluster in GCP.
Below is the deployment file.
apiVersion: v1
kind: Service
metadata:
name: mysql
labels:
app: mysql-database
spec:
type: NodePort
ports:
- port: 3306
targetPort: 3306
selector:
app: mysql-database
tier: database
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: mysql
labels:
app: mysql-database
spec:
strategy:
type: Recreate
template:
metadata:
labels:
app: mysql-database
tier: database
spec:
hostname: mysql
containers:
- image: mysql/mysql-server:5.7
name: mysql
env:
- name: "MYSQL_USER"
value: "root"
- name: "MYSQL_HOST"
value: "mysql"
- name: "MYSQL_DATABASE"
value: "xxxx"
- name: "MYSQL_PORT"
value: "3306"
- name: "MYSQL_PASSWORD"
value: "password"
- name: "MYSQL_ROOT_PASSWORD"
value: "password"
- name: "RAILS_ENV"
value: "production"
ports:
- containerPort: 5432
name: db
---
apiVersion: v1
kind: Service
metadata:
name: dgservice
labels:
app: dgservice
spec:
type: NodePort
ports:
- port: 8080
targetPort: 8080
selector:
name: dgservice
tier: dgservice
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: dgservice
labels:
app: dgservice
spec:
strategy:
type: Recreate
template:
metadata:
labels:
app: dgservice
tier: dgservice
spec:
hostname: dgservice
containers:
- image: gcr.io/sample/sample-image:check_1
name: dgservice
ports:
- containerPort: 8080
name: dgservice
---
apiVersion: v1
kind: Service
metadata:
name: dg-ui
labels:
name: dg-ui
spec:
type: NodePort
ports:
- nodePort: 30156
port: 8000
protocol: TCP
targetPort: 8000
selector:
app: dg-ui
tier: dg
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: dg-ui
labels:
app: dg-ui
spec:
strategy:
type: Recreate
template:
metadata:
labels:
app: dg-ui
tier: dg
spec:
hostname: dg-ui
containers:
- image: gcr.io/sample/sample:latest
name: dg-ui
env:
- name: "MYSQL_USER"
value: "root"
- name: "MYSQL_HOST"
value: "mysql"
- name: "MYSQL_DATABASE"
value: "xxxx"
- name: "MYSQL_PORT"
value: "3306"
- name: "MYSQL_PASSWORD"
value: "password"
- name: "MYSQL_ROOT_PASSWORD"
value: "password"
- name: "RAILS_ENV"
value: "production"
- name: "DG_SERVICE_HOST"
value: "dgservice"
ports:
- containerPort: 8000
name: dg-ui
The image is being pulled successfully from GCR as well.
The connection between mysql and ui service also works fine and my data's are getting migrated without any issues. But the connection is not established between the service and the ui.
Why ui is not able to access service in my application?

Answer 1

As your deployment has the following lables so service need to have same labels in order to create endpoint object
endpoints are the API object behind a service. The endpoints are where a service will route connections to when a connection is made to the ClusterIP of a service
Following are the labels of deployments
labels:
app: dgservice
tier: dgservice
New Service definition with correct labels
apiVersion: v1
kind: Service
metadata:
name: dgservice
labels:
app: dgservice
spec:
type: NodePort
ports:
- port: 8080
targetPort: 8080
selector:
app: dgservice
tier: dgservice

Answer 2

I am assuming by "service" you are referring to your "dgservice". With the yaml presented above, I believe you also need to specify the DG_SERVICE_PORT (port 8080) to correctly access "dgservice".
As mentioned by Suresh in the comments, you should expose internal services using ClusterIP type. The NodePort is a superset of ClusterIP, and will expose the service internally to your cluster at service-name:port, and externally at node-ip:nodeport, targeting your deployment/pod at targetport.