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diff --git a/APACHE_1_3_42/htdocs/manual/vhosts/details.html b/APACHE_1_3_42/htdocs/manual/vhosts/details.html new file mode 100644 index 0000000000..781d8b4168 --- /dev/null +++ b/APACHE_1_3_42/htdocs/manual/vhosts/details.html @@ -0,0 +1,397 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> + +<html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta name="generator" content="HTML Tidy, see www.w3.org" /> + + <title>An In-Depth Discussion of Virtual Host Matching</title> + </head> + <!-- Background white, links blue (unvisited), navy (visited), red (active) --> + + <body bgcolor="#FFFFFF" text="#000000" link="#0000FF" + vlink="#000080" alink="#FF0000"> + <!--#include virtual="header.html" --> + + <h1 align="CENTER">An In-Depth Discussion of Virtual Host + Matching</h1> + + <p>The virtual host code was completely rewritten in + <strong>Apache 1.3</strong>. This document attempts to explain + exactly what Apache does when deciding what virtual host to + serve a hit from. With the help of the new <a + href="../mod/core.html#namevirtualhost"><samp>NameVirtualHost</samp></a> + directive virtual host configuration should be a lot easier and + safer than with versions prior to 1.3.</p> + + <p>If you just want to <cite>make it work</cite> without + understanding how, here are <a href="examples.html">some + examples</a>.</p> + + <h3>Config File Parsing</h3> + + <p>There is a <em>main_server</em> which consists of all the + definitions appearing outside of + <code><VirtualHost></code> sections. There are virtual + servers, called <em>vhosts</em>, which are defined by <a + href="../mod/core.html#virtualhost"><samp><VirtualHost></samp></a> + sections.</p> + + <p>The directives <a + href="../mod/core.html#port"><samp>Port</samp></a>, <a + href="../mod/core.html#servername"><samp>ServerName</samp></a>, + <a + href="../mod/core.html#serverpath"><samp>ServerPath</samp></a>, + and <a + href="../mod/core.html#serveralias"><samp>ServerAlias</samp></a> + can appear anywhere within the definition of a server. However, + each appearance overrides the previous appearance (within that + server).</p> + + <p>The default value of the <code>Port</code> field for + main_server is 80. The main_server has no default + <code>ServerPath</code>, or <code>ServerAlias</code>. The + default <code>ServerName</code> is deduced from the servers IP + address.</p> + + <p>The main_server Port directive has two functions due to + legacy compatibility with NCSA configuration files. One + function is to determine the default network port Apache will + bind to. This default is overridden by the existence of any <a + href="../mod/core.html#listen"><code>Listen</code></a> + directives. The second function is to specify the port number + which is used in absolute URIs during redirects.</p> + + <p>Unlike the main_server, vhost ports <em>do not</em> affect + what ports Apache listens for connections on.</p> + + <p>Each address appearing in the <code>VirtualHost</code> + directive can have an optional port. If the port is unspecified + it defaults to the value of the main_server's most recent + <code>Port</code> statement. The special port <samp>*</samp> + indicates a wildcard that matches any port. Collectively the + entire set of addresses (including multiple <samp>A</samp> + record results from DNS lookups) are called the vhost's + <em>address set</em>.</p> + + <p>Unless a <a + href="../mod/core.html#namevirtualhost">NameVirtualHost</a> + directive is used for a specific IP address the first vhost + with that address is treated as an IP-based vhost. In 1.3.13 + and later that includes the IP address <code>*</code>.</p> + + <p>If name-based vhosts should be used a + <code>NameVirtualHost</code> directive <em>must</em> appear + with the IP address set to be used for the name-based vhosts. + In other words, you must specify the IP address that holds the + hostname aliases (CNAMEs) for your name-based vhosts via a + <code>NameVirtualHost</code> directive in your configuration + file.</p> + + <p>Multiple <code>NameVirtualHost</code> directives can be used + each with a set of <code>VirtualHost</code> directives but only + one <code>NameVirtualHost</code> directive should be used for + each specific IP:port pair.</p> + + <p>The ordering of <code>NameVirtualHost</code> and + <code>VirtualHost</code> directives is not important which + makes the following two examples identical (only the order of + the <code>VirtualHost</code> directives for <em>one</em> + address set is important, see below):</p> +<pre> + | + NameVirtualHost 111.22.33.44 | <VirtualHost 111.22.33.44> + <VirtualHost 111.22.33.44> | # server A + # server A | </VirtualHost> + ... | <VirtualHost 111.22.33.55> + </VirtualHost> | # server C + <VirtualHost 111.22.33.44> | ... + # server B | </VirtualHost> + ... | <VirtualHost 111.22.33.44> + </VirtualHost> | # server B + | ... + NameVirtualHost 111.22.33.55 | </VirtualHost> + <VirtualHost 111.22.33.55> | <VirtualHost 111.22.33.55> + # server C | # server D + ... | ... + </VirtualHost> | </VirtualHost> + <VirtualHost 111.22.33.55> | + # server D | NameVirtualHost 111.22.33.44 + ... | NameVirtualHost 111.22.33.55 + </VirtualHost> | + | +</pre> + + <p>(To aid the readability of your configuration you should + prefer the left variant.)</p> + + <p>After parsing the <code>VirtualHost</code> directive, the + vhost server is given a default <code>Port</code> equal to the + port assigned to the first name in its <code>VirtualHost</code> + directive.</p> + + <p>The complete list of names in the <code>VirtualHost</code> + directive are treated just like a <code>ServerAlias</code> (but + are not overridden by any <code>ServerAlias</code> statement) + if all names resolve to the same address set. Note that + subsequent <code>Port</code> statements for this vhost will not + affect the ports assigned in the address set.</p> + + <p>During initialization a list for each IP address is + generated and inserted into an hash table. If the IP address is + used in a <code>NameVirtualHost</code> directive the list + contains all name-based vhosts for the given IP address. If + there are no vhosts defined for that address the + <code>NameVirtualHost</code> directive is ignored and an error + is logged. For an IP-based vhost the list in the hash table is + empty.</p> + + <p>Due to a fast hashing function the overhead of hashing an IP + address during a request is minimal and almost not existent. + Additionally the table is optimized for IP addresses which vary + in the last octet.</p> + + <p>For every vhost various default values are set. In + particular:</p> + + <ol> + <li>If a vhost has no <a + href="../mod/core.html#serveradmin"><code>ServerAdmin</code></a>, + <a + href="../mod/core.html#resourceconfig"><code>ResourceConfig</code></a>, + <a + href="../mod/core.html#accessconfig"><code>AccessConfig</code></a>, + <a href="../mod/core.html#timeout"><code>Timeout</code></a>, + <a + href="../mod/core.html#keepalivetimeout"><code>KeepAliveTimeout</code></a>, + <a + href="../mod/core.html#keepalive"><code>KeepAlive</code></a>, + <a + href="../mod/core.html#maxkeepaliverequests"><code>MaxKeepAliveRequests</code></a>, + or <a + href="../mod/core.html#sendbuffersize"><code>SendBufferSize</code></a> + directive then the respective value is inherited from the + main_server. (That is, inherited from whatever the final + setting of that value is in the main_server.)</li> + + <li>The "lookup defaults" that define the default directory + permissions for a vhost are merged with those of the + main_server. This includes any per-directory configuration + information for any module.</li> + + <li>The per-server configs for each module from the + main_server are merged into the vhost server.</li> + </ol> + Essentially, the main_server is treated as "defaults" or a + "base" on which to build each vhost. But the positioning of + these main_server definitions in the config file is largely + irrelevant -- the entire config of the main_server has been + parsed when this final merging occurs. So even if a main_server + definition appears after a vhost definition it might affect the + vhost definition. + + <p>If the main_server has no <code>ServerName</code> at this + point, then the hostname of the machine that httpd is running + on is used instead. We will call the <em>main_server address + set</em> those IP addresses returned by a DNS lookup on the + <code>ServerName</code> of the main_server.</p> + + <p>For any undefined <code>ServerName</code> fields, a + name-based vhost defaults to the address given first in the + <code>VirtualHost</code> statement defining the vhost.</p> + + <p>Any vhost that includes the magic <samp>_default_</samp> + wildcard is given the same <code>ServerName</code> as the + main_server.</p> + + <h3>Virtual Host Matching</h3> + + <p>The server determines which vhost to use for a request as + follows:</p> + + <h4>Hash table lookup</h4> + + <p>When the connection is first made by a client, the IP + address to which the client connected is looked up in the + internal IP hash table.</p> + + <p>If the lookup fails (the IP address wasn't found) the + request is served from the <samp>_default_</samp> vhost if + there is such a vhost for the port to which the client sent the + request. If there is no matching <samp>_default_</samp> vhost + the request is served from the main_server.</p> + + <p>In Apache 1.3.13 and later, if the IP address is not found + in the hash table then the match against the port number may + also result in an entry corresponding to a + <code>NameVirtualHost *</code>, which is subsequently handled + like other name-based vhosts.</p> + + <p>If the lookup succeeded (a corresponding list for the IP + address was found) the next step is to decide if we have to + deal with an IP-based or a name-base vhost.</p> + + <h4>IP-based vhost</h4> + + <p>If the entry we found has an empty name list then we have + found an IP-based vhost, no further actions are performed and + the request is served from that vhost.</p> + + <h4>Name-based vhost</h4> + + <p>If the entry corresponds to a name-based vhost the name list + contains one or more vhost structures. This list contains the + vhosts in the same order as the <code>VirtualHost</code> + directives appear in the config file.</p> + + <p>The first vhost on this list (the first vhost in the config + file with the specified IP address) has the highest priority + and catches any request to an unknown server name or a request + without a <code>Host:</code> header field.</p> + + <p>If the client provided a <code>Host:</code> header field the + list is searched for a matching vhost and the first hit on a + <code>ServerName</code> or <code>ServerAlias</code> is taken + and the request is served from that vhost. A <code>Host:</code> + header field can contain a port number, but Apache always + matches against the real port to which the client sent the + request.</p> + + <p>If the client submitted a HTTP/1.0 request without + <code>Host:</code> header field we don't know to what server + the client tried to connect and any existing + <code>ServerPath</code> is matched against the URI from the + request. The first matching path on the list is used and the + request is served from that vhost.</p> + + <p>If no matching vhost could be found the request is served + from the first vhost with a matching port number that is on the + list for the IP to which the client connected (as already + mentioned before).</p> + + <h4>Persistent connections</h4> + The IP lookup described above is only done <em>once</em> for a + particular TCP/IP session while the name lookup is done on + <em>every</em> request during a KeepAlive/persistent + connection. In other words a client may request pages from + different name-based vhosts during a single persistent + connection. + + <h4>Absolute URI</h4> + + <p>If the URI from the request is an absolute URI, and its + hostname and port match the main server or one of the + configured virtual hosts <em>and</em> match the address and + port to which the client sent the request, then the + scheme/hostname/port prefix is stripped off and the remaining + relative URI is served by the corresponding main server or + virtual host. If it does not match, then the URI remains + untouched and the request is taken to be a proxy request.</p> + + <h3>Observations</h3> + + <ul> + <li>A name-based vhost can never interfere with an IP-base + vhost and vice versa. IP-based vhosts can only be reached + through an IP address of its own address set and never + through any other address. The same applies to name-based + vhosts, they can only be reached through an IP address of the + corresponding address set which must be defined with a + <code>NameVirtualHost</code> directive.</li> + + <li><code>ServerAlias</code> and <code>ServerPath</code> + checks are never performed for an IP-based vhost.</li> + + <li>The order of name-/IP-based, the <samp>_default_</samp> + vhost and the <code>NameVirtualHost</code> directive within + the config file is not important. Only the ordering of + name-based vhosts for a specific address set is significant. + The one name-based vhosts that comes first in the + configuration file has the highest priority for its + corresponding address set.</li> + + <li>For security reasons the port number given in a + <code>Host:</code> header field is never used during the + matching process. Apache always uses the real port to which + the client sent the request.</li> + + <li>If a <code>ServerPath</code> directive exists which is a + prefix of another <code>ServerPath</code> directive that + appears later in the configuration file, then the former will + always be matched and the latter will never be matched. (That + is assuming that no <code>Host:</code> header field was + available to disambiguate the two.)</li> + + <li>If two IP-based vhosts have an address in common, the + vhost appearing first in the config file is always matched. + Such a thing might happen inadvertently. The server will give + a warning in the error logfile when it detects this.</li> + + <li>A <code>_default_</code> vhost catches a request only if + there is no other vhost with a matching IP address + <em>and</em> a matching port number for the request. The + request is only caught if the port number to which the client + sent the request matches the port number of your + <code>_default_</code> vhost which is your standard + <code>Port</code> by default. A wildcard port can be + specified (<em>i.e.</em>, <code>_default_:*</code>) to catch + requests to any available port. In Apache 1.3.13 and later + this also applies to <code>NameVirtualHost *</code> + vhosts.</li> + + <li>The main_server is only used to serve a request if the IP + address and port number to which the client connected is + unspecified and does not match any other vhost (including a + <code>_default_</code> vhost). In other words the main_server + only catches a request for an unspecified address/port + combination (unless there is a <code>_default_</code> vhost + which matches that port).</li> + + <li>A <code>_default_</code> vhost or the main_server is + <em>never</em> matched for a request with an unknown or + missing <code>Host:</code> header field if the client + connected to an address (and port) which is used for + name-based vhosts, <em>e.g.</em>, in a + <code>NameVirtualHost</code> directive.</li> + + <li>You should never specify DNS names in + <code>VirtualHost</code> directives because it will force + your server to rely on DNS to boot. Furthermore it poses a + security threat if you do not control the DNS for all the + domains listed. There's <a href="../dns-caveats.html">more + information</a> available on this and the next two + topics.</li> + + <li><code>ServerName</code> should always be set for each + vhost. Otherwise A DNS lookup is required for each + vhost.</li> + </ul> + + <h3>Tips</h3> + + <p>In addition to the tips on the <a + href="../dns-caveats.html#tips">DNS Issues</a> page, here are + some further tips:</p> + + <ul> + <li>Place all main_server definitions before any + <code>VirtualHost</code> definitions. (This is to aid the + readability of the configuration -- the post-config merging + process makes it non-obvious that definitions mixed in around + virtual hosts might affect all virtual hosts.)</li> + + <li>Group corresponding <code>NameVirtualHost</code> and + <code>VirtualHost</code> definitions in your configuration to + ensure better readability.</li> + + <li>Avoid <code>ServerPaths</code> which are prefixes of + other <code>ServerPaths</code>. If you cannot avoid this then + you have to ensure that the longer (more specific) prefix + vhost appears earlier in the configuration file than the + shorter (less specific) prefix (<em>i.e.</em>, "ServerPath + /abc" should appear after "ServerPath /abc/def").</li> + </ul> + <!--#include virtual="footer.html" --> + </body> +</html> + |