有没有办法向 kube-dns 添加任意记录? [英] Is there a way to add arbitrary records to kube-dns?

问题描述

我会用一种非常具体的方式来解释我的问题，但我认为这比用抽象的方式解释要具体一些...

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...

假设有一个 MongoDB 副本集位于 Kubernetes 集群之外但位于网络中.副本集所有成员的ip地址由app服务器和db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/过渡阶段，我需要从 kubernetes pod 访问那些 mongo db 服务器.但是，kubernetes 似乎不允许向 pods/containers 中的/etc/hosts 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 副本集已经在处理大数据集，不能在集群中创建新的副本集.

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，所以我想应该避免更改 kube-dns 命名空间中的任何资源.配置或替换 kube-dns 以适合我的需要是最后一件事.

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.

有没有办法在 Kubernetes 集群中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?

这只是一个想法，但如果 kube2sky 可以读取 configmap 的一些条目并将它们用作 dns 记录，那就太好了.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/issues 引用了这个问题/12337

推荐答案

UPDATE: 2017-07-03 Kunbernetes 1.7 现在支持 使用 HostAliases 将条目添加到 Pod/etc/hosts.

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，而是/etc/hosts.无论如何，到目前为止，以下技巧似乎有效......

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 系统存在竞争条件.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

不要忘记chmod a+x ensure_hosts.sh.

3) 添加包装脚本 start.sh 您的图像

3) Add a wrapper script start.sh your image

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

不要忘记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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