1. 场景
后端存在N个tomcat实例，前端通过nginx反向代理和负载均衡。
tomcat1 tomcatN
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nginx
2. 需求
为了保护后端应用，tomcat实例只允许前端nginx服务器IP访问，其他任何地址的访问都被拒绝。
3. 实现
编辑${TOMCAT_HOME}/conf/server.xml，添加org.apache.catalina.valves.RemoteAddrValve配置，如下所示：
<Host name="localhost" appBase="webapps"
unpackWARs="true" autoDeploy="true"> <!-- SingleSignOn valve, share authentication between web applications
Documentation at: /docs/config/valve.html -->
<!--
<Valve className="org.apache.catalina.authenticator.SingleSignOn" />
--> <!-- Access log processes all example.
Documentation at: /docs/config/valve.html
Note: The pattern used is equivalent to using pattern="common" -->
<Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
prefix="localhost_access_log." suffix=".txt"
pattern="%h %l %u %t "%r" %s %b" /> <!-- 限制指定IP地址访问Tomcat -->
<Valve className="org.apache.catalina.valves.RemoteAddrValve"
allow="127.0.0.1"
deny=""/>
</Host>
4. 原理
（1）概述
在tomcat中存在一个与容器关联的组件Valve，该组件用于处理request请求。源码注释为：
详见tomcat请求处理时序图：http://tomcat.apache.org/tomcat-8.5-doc/architecture/requestProcess/request-process.png。
因此，我们可以通过添加指定Valve实现，用于在处理request请求时实现相应功能。
例如：在这里通过在<Host>元素中添加org.apache.catalina.valves.RemoteAddrValve实现限制指定IP地址访问应用程序。
（2）Valve类图
（3）源码解读
org.apache.catalina.valves.RemoteAddrValve实现Valve处理request请求接口：
@Override
public void invoke(Request request, Response response) throws IOException, ServletException {
String property;
if (addConnectorPort) {
property = request.getRequest().getRemoteAddr() + ";" + request.getConnector().getPort();
} else {
property = request.getRequest().getRemoteAddr();
}
process(property, request, response);
}
org.apache.catalina.valves.RequestFilterValve process实现：
protected void process(String property, Request request, Response response)
throws IOException, ServletException { if (isAllowed(property)) {
getNext().invoke(request, response);
return;
} if (getLog().isDebugEnabled()) {
getLog().debug(sm.getString("requestFilterValve.deny",
request.getRequestURI(), property));
} // Deny this request
denyRequest(request, response);
}
public boolean isAllowed(String property) {
// Use local copies for thread safety
Pattern deny = this.deny;
Pattern allow = this.allow;
// Check the deny patterns, if any
if (deny != null && deny.matcher(property).matches()) {
return false;
}
// Check the allow patterns, if any
if (allow != null && allow.matcher(property).matches()) {
return true;
}
// Allow if denies specified but not allows
if (deny != null && allow == null) {
return true;
}
// Deny this request
return false;
}