UnknownHostException in kubernetes

Question

Im using microservice in kubernete and docker and I got an UnknownHostException when Zuul (gateway) forward request data to service I can't ping to service container by pod name (but when i use docker swarm instead of Kubernetes, i can ping by host name normally)

This is my service yaml file

apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: merchantservice
  labels:
    run: merchantservice
spec:
  template:
    metadata:
      labels:
        name: merchantservice
    spec:
      containers:
      - name: merchantservice
        image: merchantservice:latest
        ports:
        - containerPort: 8001
        env:
          - name: EUREKA_SERVER
            value: "eureka1"
          - name: EUREKA_SERVER2
            value: "eureka2"
          - name: CONFIG_SERVER
            value: "configserver"
---
apiVersion: v1
kind: Service
metadata:
  name: merchantservice
spec:
  selector:
    name: merchantservice
  ports:
    - port: 8001
      targetPort: 8001
  type: LoadBalancer

And this is error output

2019-05-28 04:29:53.443  WARN 1 --- [nio-8444-exec-6] o.s.c.n.z.filters.post.SendErrorFilter   : Error during filtering

com.netflix.zuul.exception.ZuulException: Forwarding error
...
Caused by: com.netflix.client.ClientException: null
...
Caused by: java.lang.RuntimeException: java.net.UnknownHostException: merchantservice-79cc77d9cc-224mf: Try again
    at rx.exceptions.Exceptions.propagate(Exceptions.java:57) ~[rxjava-1.3.8.jar!/:1.3.8]
    at rx.observables.BlockingObservable.blockForSingle(BlockingObservable.java:463) ~[rxjava-1.3.8.jar!/:1.3.8]
    at rx.observables.BlockingObservable.single(BlockingObservable.java:340) ~[rxjava-1.3.8.jar!/:1.3.8]
    at com.netflix.client.AbstractLoadBalancerAwareClient.executeWithLoadBalancer(AbstractLoadBalancerAwareClient.java:112) ~[ribbon-loadbalancer-2.3.0.jar!/:2.3.0]
    ... 158 common frames omitted
Caused by: java.net.UnknownHostException: merchantservice-79cc77d9cc-224mf: Try again
...

kube-dns does not create DNS records for pods, since they are ephemeral; if you want to address pods, use their IP or use a `Service` — mdaniel, May 28 '19 at 06:20
@MatthewLDaniel but why my eureka server (service discovery) still discovery service normally? In config server, im using this `server.port=8001 eureka.client.serviceUrl.defaultZone=http://${EUREKA_SERVER:localhost}:9091/eureka,http://${EUREKA_SERVER2:localhost}:9092/eureka` — Kaijin Sabrac, May 28 '19 at 06:37
I don't understand your question; what does posting `eureka.client.serviceUrl.defaultZone=` have to do with your question about resolving the DNS name of a Pod? — mdaniel, May 28 '19 at 06:50
@MatthewLDaniel the `${EUREKA_SERVER:localhost}` return eureka server hostname => it will become to `eureka.client.serviceUrl.defaultZone=http://eureka:9091/eureka` <= why this hostname `eureka` work but zuul occur exception? — Kaijin Sabrac, May 28 '19 at 07:06
@KaijinSabrac ```merchantservice-79cc77d9cc-224mft``` is the pod name not the service name. your zuul is integrated with eureka and ribbon is doing client side discovery by querying the eureka server with service name. It is getting list of host names(pod names) and making a call using the pod name instead of the pod ip, its getting failed. Kindly follow Matthew suggestion of using ip address instead of pod name. — Barath, May 28 '19 at 11:09

score 4 · Answer 1 · answered Sep 18 '19 at 10:57

4

Make sure that you have added eureka.instance.preferIpAddress = true in your application.properties file of the microservice which has to be routed via zuul.

Reference: https://cloud.spring.io/spring-cloud-netflix/multi/multi_spring-cloud-eureka-server.html#spring-cloud-eureka-server-prefer-ip-address

answered Sep 18 '19 at 10:57

Abhi

94
7

This actually worked for me !! @kaijin-sabrac Please mark this as answer if you also feel the same !! – Kiran Joshi Mar 08 '21 at 18:12
what happens if Ip changes? In k8s, the Ip of the pod will change if I created new pod – avadhut007 May 20 '21 at 10:19
IP is read via Service discovery, assuming you are using DNS based service discovery, it'll map IP from pod's service host. – Abhi May 22 '21 at 13:10

score 1 · Answer 2 · answered Sep 24 '19 at 20:27

1

in openshift you cannot hit a pod by pod-id but you can hit it by local DNS and service. ..svc.cluster.local: I think the same will work in your case. please try below

merchantservice.<bob-id/project-id>.svc.cluster.local:8081

answered Sep 24 '19 at 20:27

Sumit Bhawsar

21
1

score 1 · Answer 3 · answered Aug 06 '20 at 14:16

It seems that container id or (pod id ) in case of kubernetes is not valid DNS name however, it is valid if you use docker-compose. I think the preferred way is to add this setting to all services that will be registered in Eureka eureka.instance.prefer-ip-address=true

score 0 · Answer 4 · answered Jun 25 '19 at 12:13

0

I am posting @Matthew L Daniel answer from the comments for better visibility:

kube-dns does not create DNS records for pods, since they are ephemeral; if you want to address pods, use their IP or use a Service – Matthew L Daniel

answered Jun 25 '19 at 12:13

Wytrzymały Wiktor

11,492
5
29
37

1

I just fixed this by restart docker. This is iptables rule problem (i think) – Kaijin Sabrac Jun 28 '19 at 04:33

UnknownHostException in kubernetes

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