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-<?xml version="1.0" encoding="ISO-8859-1"?>
-<!DOCTYPE document [
- <!ENTITY project SYSTEM "project.xml">
-]>
-<document url="proxy.html">
-
- &project;
-<copyright>
- Licensed to the Apache Software Foundation (ASF) under one or more
- contributor license agreements. See the NOTICE file distributed with
- this work for additional information regarding copyright ownership.
- The ASF licenses this file to You under the Apache License, Version 2.0
- (the "License"); you may not use this file except in compliance with
- the License. You may obtain a copy of the License at
-
- http://www.apache.org/licenses/LICENSE-2.0
-
- Unless required by applicable law or agreed to in writing, software
- distributed under the License is distributed on an "AS IS" BASIS,
- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- See the License for the specific language governing permissions and
- limitations under the License.
-</copyright>
-<properties>
-<title>Reverse Proxy HowTo</title>
-<author email="rjung@apache.org">Rainer Jung</author>
-<date>$Date: 2011-03-07 16:17:11 +0100 (Mon, 07 Mar 2011) $</date>
-</properties>
-<body>
-<section name="Introduction">
-<br/>
-<p>The Apache module mod_jk and its ISAPI and NSAPI variants connect
-a web server to a backend (typically Tomcat) using the AJP protocol.
-The web server receives an HTTP(S) request and the module forwards
-the request to the backend. This function is usually called a gateway
-or a proxy, in the context of HTTP it is called a reverse proxy.
-</p>
-</section>
-<section name="Typical Problems">
-<br/>
-<p>A reverse proxy is not totally transparent to the application on
-the backend. For instance the host name and port the original client
-(e.g. browser) needs to talk to belong to the web server and not to the
-backend, so the reverse proxy talks to a different host name and port.
-When the application on the backend returns content including
-self-referential URLs using its own backend address and port, the
-client will usually not be able to use these URLs.
-</p>
-<p>Another example is the client IP address, which for the web server is the
-source IP of the incoming connection, whereas for the backend the
-connection always comes from the web server. This can be a problem, when
-the client IP is used by the backend application e.g. for security reasons.
-</p>
-</section>
-<section name="AJP as a Solution">
-<br/>
-<p>Most of these problems are automatically handled by the AJP protocol
-and the AJP connectors of the backend. The AJP protocol transports
-this communication metadata and the backend connector presents this
-metadata whenever the application asks for it using Servlet API methods.
-</p>
-<p>The following list contains the communication metadata handled by AJP
-and the ServletRequest/HttpServletRequest API calls which can be used to retrieve them:
-<ul>
-<li>local name: <code>getLocalName()</code> and <code>getLocalAddr</code>.
-This is also equal to <code>getServerName()</code>, unless a <code>Host</code> header
-is contained in the request. In this case the server name is taken from that header.
-</li>
-<li>local port: <code>getLocalPort()</code>
-This is also equal to <code>getServerPort()</code>, unless a <code>Host</code> header
-is contained in the request. In this case the server port is taken from that header
-if it contains an explicit port, or is equal to the default port of the scheme used.
-</li>
-<li>client address: <code>getRemoteAddr()</code>
-</li>
-<li>client port: <code>getRemotePort()</code>
-The remote port was initially not supported. It is available when using mod_jk 1.2.32
-with Apache or IIS (not for the NSAPI plugin) together with Tomcat version at least
-5.5.28, 6.0.20 or 7.0.0. For older versions, <code>getRemotePort()</code>
-will incorrectly return 0 or -1. As a workaround you can forward the remote port by setting
-<code>JkEnvVar REMOTE_PORT</code> and then either using
-<code>request.getAttribute("REMOTE_PORT")</code> instead of <code>getRemotePort()</code>
-or wrapping the request using a filter and overriding <code>getRemotePort()</code> with
-<code>request.getAttribute("REMOTE_PORT")</code>.
-</li>
-<li>client host: <code>getRemoteHost()</code>
-</li>
-<li>authentication type: <code>getAuthType()</code>
-</li>
-<li>remote user: <code>getRemoteUser()</code>,
-if <code>tomcatAuthentication="false"</code>
-</li>
-<li>protocol: <code>getProtocol()</code>
-</li>
-<li>HTTP method: <code>getMethod()</code>
-</li>
-<li>URI: <code>getRequestURI()</code>
-</li>
-<li>HTTPS used: <code>isSecure()</code>, <code>getScheme()</code>
-</li>
-<li>query string: <code>getQueryString()</code>
-</li>
-</ul>
-The following additional SSL-related data will be made available by Apache and forwarded by mod_jk only
-if you set <code>SSLOptions +StdEnvVars</code>. For the certificate information you also need
-to set <code>SSLOptions +ExportCertData</code>.
-<ul>
-<li>SSL cipher: <code>getAttribute(javax.servlet.request.cipher_suite)</code>
-</li>
-<li>SSL key size: <code>getAttribute(javax.servlet.request.key_size)</code>.
-Can be disabled using <code>JkOptions -ForwardKeySize</code>.
-</li>
-<li>SSL client certificate: <code>getAttribute(javax.servlet.request.X509Certificate)</code>.
-If you want the whole certificate chain, then you need to also set <code>JkOptions ForwardSSLCertChain</code>.
-It is likely, that in this case you also need to adjust the maximal AJP packet size
-using the worker attribute <a href="../reference/workers.html">max_packet_size</a>.
-</li>
-<li>SSL session ID: <code>getAttribute(javax.servlet.request.ssl_session)</code>.
-This is for Tomcat, it has not yet been standardized.
-</li>
-</ul>
-</p>
-</section>
-<section name="Fine Tuning">
-<br/>
-<p>In some situations this is not enough though. Assume there is another
-less clever reverse proxy in front of your web server, for instance an
-HTTP load balancer or similar device which also serves as an SSL accelerator.
-</p>
-<p>Then you are sure that all your clients use HTTPS, but your web server doesn't
-know about that. All it can see is requests coming from the accelerator using
-plain HTTP.
-</p>
-<p>Another example would be a simple reverse proxy in front of your web server,
-so that the client IP address that your web server sees is always the IP address
-of this reverse proxy, and not of the original client. Often such reverse proxies
-generate an additional HTTP header, like <code>X-Forwareded-for</code> which
-contains the original client IP address (or a list of IP addresses, if there are
-more cascading reverse proxies in front). It would be nice, if we could use the
-content of such a header as the client IP address to pass to the backend.
-</p>
-<p>So we might need to manipulate some of the data that AJP sends to the backend.
-When using mod_jk inside Apache httpd you can use several httpd environment
-variables to let mod_jk know, which data it should forward. These environment variables
-can be set by the httpd directives SetEnv or SetEnvIf, but also in a very flexible
-way using mod_rewrite (since httpd 2.x it can not only test against environment
-variables, but also set them).
-</p>
-<p>The following list contains all environment variables mod_jk checks, before
-sending data to the backend:
-<ul>
-<li>JK_LOCAL_NAME: the local name
-</li>
-<li>JK_LOCAL_PORT: the local port
-</li>
-<li>JK_REMOTE_HOST: the client host
-</li>
-<li>JK_REMOTE_ADDR: the client address
-</li>
-<li>JK_AUTH_TYPE: the authentication type
-</li>
-<li>JK_REMOTE_USER: the remote user
-</li>
-<li>HTTPS: On (case-insensitive) to indicate, that HTTPS is used
-</li>
-<li>SSL_CIPHER: the SSL cipher
-</li>
-<li>SSL_CIPHER_USEKEYSIZE: the SSL key size
-</li>
-<li>SSL_CLIENT_CERT: the SSL client certificate
-</li>
-<li>SSL_CLIENT_CERT_CHAIN_: prefix of variable names, containing
-the client cerificate chain
-</li>
-<li>SSL_SESSION_ID: the SSL session ID
-</li>
-</ul>
-</p>
-<p>Remember: in general you don't need to set them. The module retrieves the data automatically
-from the web server. Only in case you want to change this data, you can overwrite it by
-using these variables.
-</p>
-<p>Some of these variables might also be used by other web server modules. All
-variables whose name does not begin with "JK" are set directly by Apache httpd.
-If you want to change the data, but do not want to negatively influence the behaviour
-of other modules, you can change the names of all variables mod_jk uses to private ones.
-For the details see the <a href="../reference/apache.html">Apache reference</a> page.
-</p>
-<p>All variables, that are not SSL-related have only been introduced in version 1.2.27.
-</p>
-<p>Finally there is a shortcut to forward the local IP of the web server as the remote IP.
-This can be useful, e.g. when using the Tomcat remote address valve for allowing connections
-only from registered Apache web servers. This feature is activated by setting
-<code>JkOptions ForwardLocalAddress</code>.
-</p>
-</section>
-<section name="Tomcat AJP Connector Settings">
-<br/>
-<p>As an alternative to using the environment variables described in the previous section
-(which do only exist when using Apache httpd), you can also configure Tomcat to overwrite
-some of the communications data forwarded by mod_jk. The AJP connector in Tomcat's <code>server.xml</code>
-allows to set the <a href="http://tomcat.apache.org/tomcat-6.0-doc/config/ajp.html#Attributes">following properties</a>:
-<ul>
-<li>proxyName: server name as returned by <code>getServerName()</code>
-</li>
-<li>proxyPort: server port as returned by <code>getServerPort()</code>
-</li>
-<li>scheme: protocol scheme as returned by <code>getScheme()</code>
-</li>
-<li>secure: set to "true", if you wish <code>isSecure()</code> to return "true".
-</li>
-</ul>
-Remember: in general you don't need to set those. AJP automatically handles all cases
-where the web server running mod_jk knows the right data.
-</p>
-</section>
-<section name="URL Handling">
-<br/>
-<subsection name="URL Rewriting">
-<p>Sometimes one want to change path components of the URLs under which an application
-is available. Especially if a web application is deployed as some context, say <code>/myapp</code>,
-marketing prefers short URLs, so want the application to be directly available under
-<code>http://www.mycompany.com/</code>. Although you can deploy the application as the so-called
-ROOT context, which will be directly available at "/", admins often prefer not to use
-the ROOT context, e.g. because only one application can be the root context (per host).
-</p>
-<p>The procedure to change the URLs in the reverse proxy is tedious, because often
-an application produces self-referential URLs, which then include the path components
-which you tried to hide to the outside world. Nevertheless, if you absolutely need to do it,
-here are the steps.
-</p>
-<p>Case A: You need to make the application available at a simple URL, but it is OK, if
-users proceed using the more complex URLs, as long as they don't have to type them in.
-That's the easy case, and if this suffices to you, you're lucky. Use a simply RedirectMatch
-for Apache httpd:
-</p>
-<source>
-RedirectMatch ^/$ http://www.mycompany.com/myapp/
-</source>
-<p>Your application will then be available under <code>http://www.mycompany.com/</code>,
-and each visitor will be immediately redirected to the real URL
-<code>http://www.mycompany.com/myapp/</code>
-</p>
-<p>Case B: You need to hide path components for all requests going to the application.
-Here's the recipe for the case, where you want to hide the first path component
-<code>/myapp</code>. More complex manipulations are left as an exercise to the reader.
-First the solution for the case of Apache httpd:
-</p>
-<p>1. Use <a href="http://httpd.apache.org/docs/2.2/mod/mod_rewrite.html"><code>mod_rewrite</code></a>
-to add <code>/myapp</code> to all requests before forwarding to the backend:
-</p>
-<source>
-# Don't forget the PT flag! (pass through)
-RewriteRule ^/(.*) http://www.mycompany.com/myapp/$1 [PT]
-</source>
-<p>2. Use <a href="http://httpd.apache.org/docs/2.2/mod/mod_headers.html"><code>mod_headers</code></a>
-to rewrite any HTTP redirects your application might return. Such redirects typically contain
-the path components you want to hide, because by the HTTP standard, redirects always need to include
-the full URL, and your application is not aware of the fact, that your clients talk to it via
-some shortened URL. An HTTP redirect is done with a special response header named <code>Location</code>.
-We rewrite the Location headers of our responses:
-</p>
-<source>
-# Keep protocol, server and port if present,
-# but insert our webapp name before the rest of the URL
-Header edit Location ^([^/]*//[^/]*)?/(.*)$ $1/myapp/$2
-</source>
-<p>3. Use <code>mod_headers</code> again, to rewrite the paths contained in any cookies,
-your application might set. Such cookie paths again might contain
-the path components you want to hide.
-A cookie is set with the HTTP response header named <code>Set-Cookie</code>.
-We rewrite the Set-Cookie headers of our responses:
-</p>
-<source>
-# Fix the cookie path
-Header edit Set-Cookie "^(.*; Path=/)(.*)" $1/myapp/$2
-</source>
-<p>3. Some applications might contain hard coded absolute links.
-In this case check, whether you find a configuration item for your web framework
-to configure the base URL. If not, your only chance is to parse all response
-content bodies and do search and replace. This is fragile and very resource intensive.
-If you really need to do this, you can use
-<a href="http://apache.webthing.com/mod_proxy_html/"><code>mod_proxy_html</code></a>,
-<a href="http://httpd.apache.org/docs/2.2/mod/mod_substitute.html"><code>mod_substitute</code></a>
-or <a href="http://blogs.sun.com/basant/entry/using_mod_sed_to_filter"><code>mod_sed</code></a>
-for this task.
-</p>
-<p>If you are using Microsoft IIS as a web server, the ISAPI plugin provides a way
-of doing the first step with a builtin feature. You define a mapping file for simple prefix
-changes like this:
-</p>
-<source>
-# Add a context prefix to all requests ...
-/=/myapp/
-# ... or change some prefix ...
-/oldapp/=/myapp/
-</source>
-<p>and then put the name of the file in the <code>rewrite_rule_file</code> entry of the registry or your
-<code>isapi_redirect.properties</code> file. In you <code>uriworkermap.properties</code> file, you
-still need to map the URLs as they are before rewriting!
-</p>
-<p>More complex rewrites can be done using the same file, but with regular expressions. A leading
-tilde sign '<code>~</code>', indicates, that you are using a regular expression:
-</p>
-<source>
-# Use a regular expression rewrite
-~/oldapps([0-9]*)/=/newapps$1/
-</source>
-<p>There is no support for Steps 2 (rewriting redirect responses) or 3 (rewriting cookie paths).
-</p>
-</subsection>
-<subsection name="URL Encoding">
-<p>Some types of problems are triggered by the use of encoded URLs
-(see <a href="http://en.wikipedia.org/wiki/Percent-encoding">percent encoding</a>).
-For the same location there exist
-a lot of different URLs which are equivalent. The reverse proxy needs to inspect the URL in order
-to apply its own authentication rules and to decide, to which backend it should send the request
-(or whether it should handle it itself). Therefore the request URL first is normalized:
-percent encoded characters are decoded, <code>/./</code> is replaced by <code>/</code>,
-<code>/XXX/../</code> is replaced by <code>/</code> and similar manipulations of the URL are done.
-After that, the web server might apply rewrite rules to further change the URL in less obvious ways.
-Finally there is no more way to put the resulting URL in an encoding, which is "similar" to
-the one which was used for the original URL.
-</p>
-<p>
-For historical reasons, there have been several alternatives, how mod_jk and the ISAPI
-plugin encoded the resulting URL before sending it to the backend. They could be chosen via
-<code>JkOptions</code> (Apache httpd) or <code>uri_select</code> (ISAPI). None of those historical
-encodings are recommended, because they have either negative functionality implications or
-pose a security risk. The default encoding since version 1.2.24 is <code>ForwardURIProxy</code>
-(Apache httpd) or <code>proxy</code> (ISAPI) and it is strongly recommended to keep the default
-and remove all old explicit settings.
-</p>
-</subsection>
-</section>
-<section name="Request Attributes">
-<br/>
-<p>
-You can also add more attributes to any request you are forwarding when using Apache httpd.
-For this use the <code>JkEnvVar</code> directive (for details see the
-<a href="../reference/apache.html">Apache reference</a> page). Such request attributes can be
-retrieved on the Tomcat side via request.getAttribute(attributeName).
-Note that their names will not be listed in request.getAttributeNames()!
-</p>
-</section>
-</body>
-</document>