How to add custom host entries to kubernetes Pods?

Question

My application communicates to some services via hostnames. When running my application as a docker container i used to add hostnames to the /etc/hosts of the hostmachine and run the container using --net=host.

Now I'm running my containers in kubernetes cluster. I would like to know how can i add the /etc/hosts entries to the pod via yaml.

I'm using kubernetes v1.5.3.

score 12 · Answer 1 · answered Feb 12 '18 at 11:24

12

From k8s 1.7 you can add hostAliases. Example from the docs:

apiVersion: v1
kind: Pod
metadata:
  name: hostaliases-pod
spec:
  restartPolicy: Never
  hostAliases:
  - ip: "127.0.0.1"
    hostnames:
    - "foo.local"
    - "bar.local"
  - ip: "10.1.2.3"
    hostnames:
    - "foo.remote"
    - "bar.remote"

answered Feb 12 '18 at 11:24

isalgueiro

1,973
16
20

Is this a new pod I have to add in current cluster ? – Rmahajan Dec 11 '19 at 09:13
No, that's an example on how to add custom host entries – isalgueiro Dec 11 '19 at 09:51

score 1 · Answer 2 · answered Apr 13 '17 at 12:12

1

Host files are going to give you problems, but if you really need to, you could use a configmap.

Add a configmap like so

apiVersion: v1
kind: ConfigMap
metadata:
  name: my-app-hosts-file-configmap
data:
  hosts: |-
    192.168.0.1 gateway
    127.0.0.1 localhost

Then mount that inside your pod, like so:

  volumeMounts:
    - name: my-app-hosts-file
      mountPath: /etc/
volumes:
  - name: my-app-hosts-file
    configMap:
    name: my-app-hosts-file-configmap

answered Apr 13 '17 at 12:12

jaxxstorm

12,422
5
57
67

2

But this will override the default hosts file which contains the hostname of the pod. – Bin Wang May 17 '17 at 09:01
Did you found any workaround to retain the hostname of the pod? – Shoaib Khan Jun 01 '18 at 07:35

score 1 · Accepted Answer · edited Jul 17 '17 at 20:09

1

This works and also looks simpler:

kind: Service
apiVersion: v1 
metadata:
    name: {HOST_NAME} 
    spec:
      ports:
        - protocol: TCP
          port: {PORT}
          targetPort: {PORT}
      type: ExternalName
      externalName: {EXTERNAL_IP}

Now you can use the HOST_NAME from the pod directly to access the external machine.

edited Jul 17 '17 at 20:09

J.W.F.

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24

answered Apr 18 '17 at 10:49

Karthik

929
2
12
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Alas, this wouldn't let you to add a FQDN: `Invalid value: "example.com": a DNS-1035 label must consist of lower case alphanumeric characters or '-', start with an alphabetic character, and end with an alphanumeric character (e.g. 'my-name', or 'abc-123', regex used for validation is '[a-z]([-a-z0-9]*[a-z0-9])?')` – beatcracker May 18 '18 at 11:50
1

@beatcracker For this, you can use HostAliases to solve the problem. https://kubernetes.io/docs/concepts/services-networking/add-entries-to-pod-etc-hosts-with-host-aliases/ – daemonsl Jun 27 '18 at 16:37
@sunnykrgupta I'm using terraform and its k8s provider doesn't support `HostAliases` yet. I was hoping to achieve it via this hack, but alas... – beatcracker Jun 27 '18 at 20:38

score 0 · Answer 4 · answered Mar 26 '20 at 09:40

Another approach could be to use postStart hook on the pod lifecycle as below:

lifecycle:
      postStart:
        exec:
         command: ["/bin/sh", "-c", "echo '192.168.1.10 weblogic-jms1.apizone.io' >> /etc/hosts; echo '192.168.1.20
weblogic-jms2.apizone.io' >> /etc/hosts; echo '192.168.1.30 weblogic-jms3.apizone.io' >> /etc/hosts; echo '192.168.1.40 weblogic-jms4.apizone.io' >> /etc/hosts"]

How to add custom host entries to kubernetes Pods?

4 Answers4