Kubernetes中按服务名访问redis

Question

I created a redis deployment and service in kubernetes, I can access redis from another pod by service ip, but I can't access it by service name

the redis yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: redis-deployment
  namespace: myapp-ns
spec:
  replicas: 1
  selector:
    matchLabels:
      component: redis
  template:
    metadata:
      labels:
        component: redis
    spec:
      containers:
        - name: redis
          image: redis
          ports:
            - containerPort: 6379
---
apiVersion: v1
kind: Service
metadata:
  name: redis
  namespace: myapp-ns
spec:
  type: ClusterIP
  selector:
    component: redis
  ports:
    - port: 6379
      targetPort: 6379

Answer 1

I applied your file, and I am able to ping and telnet to the service both from within the same namespace and from a different namespace. To test this, I created pods in the same namespace and in a different namespace and installed telnet and ping. Then I exec'ed into them and did the below tests:

Same Namespace

kubectl exec -it <same-namespace-pod> /bin/bash
# ping redis
PING redis.<redis-namespace>.svc.cluster.local (172.20.211.84) 56(84) bytes of data.

# telnet redis 6379
Trying 172.20.211.84...
Connected to redis.<redis-namespace>.svc.cluster.local.
Escape character is '^]'.

Different Namespace

kubectl exec -it <different-namespace-pod> /bin/bash
# ping redis.<redis-namespace>.svc.cluster.local
PING redis.test.svc.cluster.local (172.20.211.84) 56(84) bytes of data.

# telnet redis.<redis-namespace>.svc.cluster.local 6379
Trying 172.20.211.84...
Connected to redis.<redis-namespace>.svc.cluster.local.
Escape character is '^]'.

If you are not able to do that due to dns resolution issues, you could look at your /etc/resolv.conf in your pod to make sure it has the search prefixes svc.cluster.local and cluster.local

Answer 2

I created a redis deployment and service in kubernetes, I can access redis from another pod by service ip, but I can't access it by service name

Keep in mind that you can use the Service name to access the backend Pods it exposes only within the same namespace. Looking at your Deployment and Service yaml manifests, we can see they're deployed within myapp-ns namespace . It means that only from a Pod which is deployed within this namespace you can access your Service by using it's name.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: redis-deployment
  namespace: myapp-ns ### 👈
spec:
  replicas: 1
  selector:
    matchLabels:
      component: redis
  template:
    metadata:
      labels:
        component: redis
    spec:
      containers:
        - name: redis
          image: redis
          ports:
            - containerPort: 6379
---
apiVersion: v1
kind: Service
metadata:
  name: redis
  namespace: myapp-ns ### 👈
spec:
  type: ClusterIP
  selector:
    component: redis
  ports:
    - port: 6379
      targetPort: 6379

So if you deploy the following Pod :

apiVersion: v1
kind: Pod
metadata:
  name: redis-client
  namespace: myapp-ns ### 👈
spec:
  containers:
    - name: redis-client
      image: debian

you will be able to access your Service by its name, so the following commands (provided you've installed all required tools) will work:

redis-cli -h redis
telnet redis 6379

However if your redis-cliet Pod is deployed to completely different namespace , you will need to use fully qualified domain name ( FQDN ) which is build according to the rule described here :

redis-cli -h redis.myapp-ns.svc.cluster.local
telnet redis.myapp-ns.svc.cluster.local 6379