[improve][broker] Add haProxyProtocolEnabled more description

[crossoverJie]

Motivation

When using broker-proxy, I wanted to obtain the real IP address of the client, but I couldn't find much useful information in the documentation. Finally, after reading the source code, I discovered this configuration.
Therefore, the description of haProxyProtocolEnabled was added.

Modifications

Add more description.

Verifying this change

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This change is a trivial rework / code cleanup without any test coverage.

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Documentation

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Matching PR in forked repository

crossoverJie#6

[Anonymitaet]

@crossoverJie thanks for your contribution! Please attach this in the PR description as required.

[Anonymitaet]

@BewareMyPower Could you please review this PR from a technical perspective? Thank you!

[crossoverJie]

@crossoverJie thanks for your contribution! Please attach this in the PR description as required.

PTAL

[crossoverJie]

This is based on this pull request #8686 , please take a look.

@codelipenghui

[tisonkun]

This comment is correct but seems redundant - it adds no extra info from my perspective.

[crossoverJie]

This comment is correct but seems redundant - it adds no extra info from my perspective.

From the purpose of this PR, it is to provide a way to obtain the real IP address, but using the "real" keyword in proxy.conf cannot find this configuration, and the current description of haProxyProtocolEnabled is also unclear about its relation to "real IP". Unless one looks at the source code, it may be difficult to quickly locate this configuration, so I believe adding a description would be helpful.

[github-actions]

The pr had no activity for 30 days, mark with Stale label.

[codecov-commenter]

Codecov Report

Merging #19967 (6392a08) into master (00f17e8) will increase coverage by 35.33%.
The diff coverage is 100.00%.

@@              Coverage Diff              @@
##             master   #19967       +/-   ##
=============================================
+ Coverage     37.61%   72.94%   +35.33%     
- Complexity    12589    31971    +19382     
=============================================
  Files          1691     1868      +177     
  Lines        129028   138586     +9558     
  Branches      14066    15236     +1170     
=============================================
+ Hits          48530   101096    +52566     
+ Misses        74183    29450    -44733     
- Partials       6315     8040     +1725     

Flag	Coverage Δ
inttests	24.14% <100.00%> (-0.04%)	⬇️
systests	24.85% <100.00%> (+0.08%)	⬆️
unittests	72.24% <100.00%> (+39.05%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...org/apache/pulsar/broker/ServiceConfiguration.java	99.37% <ø> (+1.34%)	⬆️
.../apache/bookkeeper/mledger/impl/MetaStoreImpl.java	85.21% <100.00%> (+43.30%)	⬆️

... and 1426 files with indirect coverage changes

[tisonkun]

Merging...

Thanks for your contribution!

[michaeljmarshall]

Real might be misleading here. I think the IP address is the remote IP address from the proxy's perspective? If you agree, I think we should clarify further to prevent confusion. This is relevant when traffic ingresses to the proxy through any kind of NAT. A good example is a kubernetes load balancer with externalTrafficPolicy: cluster.

[michaeljmarshall]

I also found this setting very misleading the first time I encountered it. We're not really even using the HA Proxy protocol. It seems that we appropriated the protocol message to propagate the client IP address, which seems worth documenting since the HAProxy part is largely irrelevant here.

[michaeljmarshall]

It looks like I might be somewhat mistaken. This PR has some relevant details #16045. The edge case is that you can get the "wrong" address if the inbound connection to the pulsar proxy does not start with the HAProxy message. Here is the relevant code:

pulsar/pulsar-proxy/src/main/java/org/apache/pulsar/proxy/server/DirectProxyHandler.java

Lines 240 to 261 in 1545396

	private void writeHAProxyMessage() {
	if (proxyConnection.hasHAProxyMessage()) {
	final ByteBuf msg = encodeProxyProtocolMessage(proxyConnection.getHAProxyMessage());
	writeAndFlush(msg);
	} else {
	if (inboundChannel.remoteAddress() instanceof InetSocketAddress
	&& inboundChannel.localAddress() instanceof InetSocketAddress) {
	InetSocketAddress clientAddress = (InetSocketAddress) inboundChannel.remoteAddress();
	String sourceAddress = clientAddress.getAddress().getHostAddress();
	int sourcePort = clientAddress.getPort();
	InetSocketAddress proxyAddress = (InetSocketAddress) inboundChannel.localAddress();
	String destinationAddress = proxyAddress.getAddress().getHostAddress();
	int destinationPort = proxyAddress.getPort();
	HAProxyMessage msg = new HAProxyMessage(HAProxyProtocolVersion.V1, HAProxyCommand.PROXY,
	HAProxyProxiedProtocol.TCP4, sourceAddress, destinationAddress, sourcePort,
	destinationPort);
	final ByteBuf encodedMsg = encodeProxyProtocolMessage(msg);
	writeAndFlush(encodedMsg);
	msg.release();
	}
	}
	}