有没有一种方法可以向kube-dns添加任意记录? [英] Is there a way to add arbitrary records to kube-dns?

问题描述

我将使用一种非常具体的方式来解释我的问题，但是我认为这要比抽象地解释更好.

I will use a very specific way to explain my problem, but I think this is better to be specific than explain in an abstract way...

说，在Kubernetes集群之外但在网络中有一个MongoDB副本集.复制集的所有成员的ip地址已由应用服务器和数据库服务器中的/etc/hosts解析.

Say, there is a MongoDB replica set outside of a Kubernetes cluster but in a network. The ip addresses of all members of the replica set were resolved by /etc/hosts in app servers and db servers.

在实验/转换阶段，我需要从kubernetes容器访问那些mongo db服务器. 但是，kubernetes似乎不允许在pods/容器中的/etc/hosts中添加自定义条目.

In an experiment/transition phase, I need to access those mongo db servers from kubernetes pods. However, kubernetes doesn't seem to allow adding custom entries to /etc/hosts in pods/containers.

MongoDB副本集已在使用大型数据集，因此无法在集群中创建新副本集.

The MongoDB replica sets are already working with large data set, creating a new replica set in the cluster is not an option.

因为我使用GKE，所以我应该避免更改kube-dns命名空间中的任何资源.尝试配置或替换kube-dns以使其适合我的需求.

Because I use GKE, changing any of resources in kube-dns namespace should be avoided I suppose. Configuring or replace kube-dns to be suitable for my need are last thing to try.

在Kubernetes集群中是否可以解析自定义主机名的IP地址?

Is there a way to resolve ip address of custom hostnames in a Kubernetes cluster?

这只是一个主意，但是如果kube2sky可以读取configmap的某些条目并将其用作dns记录，那肯定很棒. 例如repl1.mongo.local: 192.168.10.100.

It is just an idea, but if kube2sky can read some entries of configmap and use them as dns records, it colud be great. e.g. repl1.mongo.local: 192.168.10.100.

我从 https://github.com/kubernetes/kubernetes/引用了此问题Issues/12337

推荐答案

更新:2017年7月3日，Kunbernetes 1.7现在支持

UPDATE: 2017-07-03 Kunbernetes 1.7 now support Adding entries to Pod /etc/hosts with HostAliases.

解决方案不是关于kube-dns的，而是/etc/hosts. 无论如何，到目前为止，以下技巧似乎仍然有效...

The solution is not about kube-dns, but /etc/hosts. Anyway, following trick seems to work so far...

更改/etc/hosts可能与kubernetes系统发生竞争.让它重试.

Changing /etc/hosts may has race condition with kubernetes system. Let it retry.

1)创建一个configMap

1) create a configMap

apiVersion: v1
kind: ConfigMap
metadata:
  name: db-hosts
data:
  hosts: |
    10.0.0.1  db1
    10.0.0.2  db2

2)添加一个名为ensure_hosts.sh的脚本.

2) Add a script named ensure_hosts.sh.

#!/bin/sh                                                                                                           
while true
do
    grep db1 /etc/hosts > /dev/null || cat /mnt/hosts.append/hosts >> /etc/hosts
    sleep 5
done

别忘了chmod a+x ensure_hosts.sh.

3)添加包装脚本start.sh您的图片

3) Add a wrapper script start.sh your image

#!/bin/sh
$(dirname "$(realpath "$0")")/ensure_hosts.sh &
exec your-app args...

别忘了chmod a+x start.sh

4)使用configmap作为卷并运行start.sh

4) Use the configmap as a volume and run start.sh

apiVersion: extensions/v1beta1
kind: Deployment
...
spec:
  template:
    ...
    spec:
      volumes:
      - name: hosts-volume
        configMap:
          name: db-hosts
      ...
      containers:
        command:
        - ./start.sh
        ...
        volumeMounts:
        - name: hosts-volume
          mountPath: /mnt/hosts.append
        ...

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