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From Pid <...@pidster.com>
Subject Re: URI mapping
Date Sun, 23 Oct 2011 20:18:41 GMT
On 23/10/2011 20:51, Mark Eggers wrote:
> ----- Original Message -----
> 
>> From: André Warnier <aw@ice-sa.com>
>> To: Tomcat Users List <users@tomcat.apache.org>
>> Cc: 
>> Sent: Sunday, October 23, 2011 5:08 AM
>> Subject: Re: URI mapping
>>
>> Let's restart from the beginning.
>>
>> You have, say, 3 Tomcat servers running, and for the sake of the example 
>> let's say that these are
>> - a Tomcat 5.x server
>> - a Tomcat 6.x server
>> - a Tomcat 7.x server
>>
>> You want to run the same applications on all of them (with identical names on 
>> each server), because for instance these are test servers serving to verify that

>> a given application runs fine under each of these Tomcat versions.
>>
>> You want to be able to choose which Tomcat server you are accessing, by means of

>> some URI prefix.
>> Example :
>> a request with URI "http://myhost/tomcat7/webapp1" should be forwarded 
>> to webapp1 on Tomcat7, while a request with URI 
>> "http://myhost/tomcat5/webapp1" should be forwarded to Tomcat5.
>>
>> Of course, once "inside" the respective Tomcat, you want this prefix 
>> to have been removed, so that the applications inside this Tomcat look similar 
>> to the same ones in other Tomcats, name-wise.
>> Example :
>> a request with URI "http://myhost/tomcat7/webapp1" should be forwarded 
>> to webapp1 on Tomcat7, whith a request URI of "/webapp1" (and not 
>> "/tomcat7/webapp1").
>>
>> For this, you set up a front-end proxy Apache httpd, which should forward the 
>> requests to individual Tomcats in function of the URI prefix, and strip this 
>> prefix while doing so.
>>
>> Preferably, you would like to do the proxying via mod_jk.
>>
>> That is a problem, because the standard proxying instructions of mod_jk (JkMount

>> e.g.), do not provide a syntax for forwarding URI's, and modifying these 
>> URIs at the same time.
>>
>> That is why Mark originally oriented you to mod_proxy and mod_proxy_ajp, which 
>> can do that, for example as :
>>
>> ProxyPass /tomcat7 ajp://tomcat7-host:8017
>> ProxyPass /tomcat6 ajp://tomcat6-host:8016
>> ProxyPass /tomcat5 ajp://tomcat7-host:8015
>> (and have each Tomcat listen on the apropriate port with its AJP Connector)
>>
>> Using the above, a request with URI "http://myhost/tomcat7/webapp1" 
>> will be forwarded to the tomcat7 server with a URI of "/webapp1", 
>> while a request with URI "http://myhost/tomcat5/webapp1" will be 
>> forwarded to the tomcat5 server with a URI (also) of "/webapp1".
>>
>> As far as I understand, this is what you want to achieve (although it is not via

>> mod_jk, but via mod_proxy_ajp instead).
>>
>> Mark however pointed out the drawbacks of modifying the URI : when one of these 
>> applications generates a self-referencing URI, it will not by default re-insert 
>> the stripped host prefix.  For example, if application "/webapp1" on 
>> tomcat7 creates a page with a link to itself like 
>> href="/webapp1/something", it will not magically know to make this 
>> into href="/tomcat7/webapp1/something".  And when this link is clicked 
>> in the browser, it will generate a request to 
>> "http://myhost/webapp1/something", and the above Proxy instructions in 
>> the front-end won't know what to do with it and will ignore it.
>>
>> And the same happens with redirects etc..
>> You can overcome this, but it is likely in the end to create more hassle than 
>> you really want.
>>
>> On the other hand, if you do /not/ modify the URI while proxying the call, then 
>> you end up with a much less easy configuration on the side of the Tomcats, as 
>> you have seen before.
>>
>> So maybe let's look at another kind of solution, involving DNS and 
>> VirtualHosts.
>>
>> Would a solution whereby you access the different Tomcats as follows be 
>> acceptable ?
>> - http://myhost-tomcat7.company.com/webapp1 is forwarded to tomcat7's 
>> webapp1
>> - http://myhost-tomcat6.company.com/webapp1 is forwarded to tomcat6's 
>> webapp1
>> - http://myhost-tomcat5.company.com/webapp1 is forwarded to tomcat5's 
>> webapp1
>>
>> If yes, then do as outlined below.
>>
>> For a start, I suppose that you want to have an Apache httpd front-end, and that

>> the Apache httpd and all tomcats, all run on the same physical host.
>>
>> Step 1 :
>> Suppose that the front-end Apache httpd host is currently known via DNS as 
>> "myhost.company.com".
>> Define 3 additional DNS aliases for it :
>> - myhost-tomcat7.company.com
>> - myhost-tomcat6.company.com
>> - myhost-tomcat5.company.com
>>
>> Step 2 :
>> define 3 new VirtualHost's in the Apache httpd front-end, one each with
>> - ServerName myhost-tomcat7.company.com
>> - ServerName myhost-tomcat6.company.com
>> - ServerName myhost-tomcat5.company.com
>>
>> (I assume that you know how to do that)
>>
>> Step 3 :
>> In each of these VirtualHost configurations, add the following lines :
>> - in the "myhost-tomcat7.company.com" host, add
>>    ProxyPass / ajp://myhost-tomcat7.company.com:8017
>>    ProxyPassReverse / ajp://myhost-tomcat7.company.com:8017
>> (and similarly for the other VirtualHost's)
>>
>> Step 4 :
>> make each of your Tomcats listen on the corresponding AJP port :
>> - tomcat7 listens on port 8017
>> - tomcat6 listens on port 8016
>> - tomcat5 listens on port 8015
>> (in their respective AJP Connector)
>>
>> The advantage of this is that you are no longer modifying the request URI's, 
>> with all the complications that this brings.
>> All you are doing is modifying the hostname:port part, and that only requires a 
>> ProxyPassReverse directive in the httpd front-end, to rewrite possible redirect 
>> headers generated by the Tomcats.
>> Also this way, self-referencing URIs generated by the Tomcats will also work, 
>> without applications modifications.
>> Cookies may still require help, check the http config help for that.
> 
> 
> Andre,
> 
> Your suggestion is how I set up multiple Tomcats (CATALINA_HOME / CATALINA_BASE) and
virtual hosts within those Tomcats. I map each of the Tomcat virtual hosts to separate named
virtual hosts on Apache HTTPD.
> 
> I use mod_jk, and each virtual host gets its own uriworkermap.properties file. That way
I can add and delete Tomcat applications on the fly for each Apache HTTPD virtual host that's
mapped to the appropriate Tomcat virtual host.
> 
> 
> Each Apache HTTPD named virtual host forwarded to a single Tomcat uses the same mod_jk
<Connector> (although I could add multiple connectors in server.xml).
> 
> 
> Each Tomcat virtual host mapped to an Apache HTTPD named virtual host gets its own manager
application. The access is controlled in part by directives in an Apache HTTPD <Location>
block. I suppose I could add another Realm for each Tomcat virtual host to control that host's
manager application as well.
> 
> I've tested this set up with simple applications and it seems to work fine. I only have
two real issues. One, I don't know any way to combine dynamic Apache HTTPD virtual hosts with
mod_jk and JkMount directives. Two, jk-status and jk-manager refer to all mod_jk connections
on a particular Apache HTTPD server.
> 
> Neither of these are show-stoppers.
> 
> My question in all of this is about cookies. I gather what you're saying is that if a
person accesses the following:
> 
> http://some-host/app (receives cookie)
> 
> Then that cookie could be used in accessing
> 
> http://other-host/app (uses cookie)
> 
> if named virtual hosts are used for some-host and other-host (mapping them to the same
IP address and port).
> 
> Is this correct?

No, I don't think so.  You'd need the two hosts to be sub-domains of the
primary cookie domain.  The jsessionid cookie is set with the server
name of the Tomcat instance, rather than a domain with variable
subdomains*, unless you have configured it otherwise (Servlet 3.0 only).


p


* E.g.

variable subdomain:  .example.com
fixed subdomain   :  host.example.com

> If so, I need to investigate how to manage this with Apache HTTPD. I suppose it's also
very unlikely (but possible) to get matching session ids from independent Tomcats running
in this environment?
> 
> If you have any pointers to the Apache HTTPD documentation concerning this, I would appreciate
it (I know, off-topic).
> 
> . . . . just my two (confused) cents
> /mde/
> 
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