Add the ability to append external IPs in node proxy mode

[stevefan1999-personal]

Description

This is regarded to this comment in the original thread of #214:

Why not just set exposed Node ips on external-ip of LoadBalancer Service?

If you set the external-ip of the LoadBalancer Service, the Kube-Proxy will modify iptables or ipvs rules on all Nodes. This is very dangerous because it disturbes the cluster network environment.

After much deliberation, I had to settle for a painful compromise.

The external-ip of the LoadBalancer Service will always stay in this mode, and the information of exposure is displayed in annotation.

We can just make that an add-in feature for people to try, we just don't have to enable it by default. It is not sure why @KONY128 suggested not to that. This is necessary for certain application that listens to load balancer status change and external IP addresses such as external-dns so I think this is more of a necessary evil.

What type of PR is this ?:

Implementation

Related links:

#214 (comment)

[stevefan1999-personal]

/assign @FeynmanZhou

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[ks-ci-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: stevefan1999-personal
To complete the pull request process, please ask for approval from feynmanzhou after the PR has been reviewed.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

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[renyunkang]

If you set the external-ip of the LoadBalancer Service, the Kube-Proxy will modify iptables or ipvs rules on all Nodes. This is very dangerous because it disturbes the cluster network environment.

As mentioned by @KONY128, setting the node IP as the external-ip for the LoadBalancer service when using kube-proxy may disrupt the original network and even paralyze the cluster network. Therefore, we do not recommend this practice.