Hi.

Could a real Apache/mod_jk specialist clear up a few questions to which
I do not seem to find a clear, definitive and explicit answer in the
documentation(s) ?

I mean, some of the things below seem to be working for me, but I would
kind of like to get some official confirmation, before I repeat them too
often to newbies on this list ;-).
I would also like to know if they represent official, supported,
likely-to-stay features, or if they are going to be obsoleted-out
anytime soon.

(It is possible that some questions overlap; the available documentation
does too sometimes).

1) I see on this list and on the Tomcat lists, a lot of questions where
people create a configuration of the following genre :

Assuming the Tomcat webapps directory is (e.g.) /var/lib/tomcatX/webapps

then, in apache.conf :

DocumentRoot /var/lib/tomcatX/webapps
or
Alias /apps "/var/lib/tomcatX/webapps"

I am of the impression that such a configuration is basically a bad
idea, because it exposes, through Apache, things that should not be
accessible by the users, such as the Tomcat webapps/xxx/WEB-INF
directories and files.
True/False ?
Elaborate ?

2) When one has the following configuration in Apache :

Alias /eg /var/lib/tomcatX/webapps/examples
<Directory /var/lib/tomcatX/webapps/examples>
 Order Allow, Deny
 Allow from all
</Directory>
JkMount /eg ajp13w
JkMount /eg/* ajp13w

my understanding is that :
- mod_jk (and Tomcat) intervene at the "content generation" phase of the
request processing.
- but "Alias" intervenes earlier, during the "URL translation" phase

Thus, if a browser requests a URL like "/eg/HelloWorld",
- Apache (by virtue of the Alias) will first translate this internally
to "/var/lib/tomcatX/webapps/examples/HelloWorld"
- then mod_jk will get a chance to generate the content of this request,
but it will decline because the URI no longer matches "/eg" or "/eg/*"
- thus Apache will (try to) serve this itself, from the directory
/var/lib/tomcatX/webapps/examples, using its default content handler
(and might fail doing so, and return "Not Found", if there is nothing in
there explictly called "HelloWorld").

True/False ?
if false, elaborate ?

3) mod_jk, for all intents and purposes within Apache, is a "content
generator", and thus intervenes *after* URI translation, access control,
authentication, authorisation, fixup.
True/False ?

4) The way in which mod_jk or Apache "decide" that a given URL is to be
handled (for content generation) by mod_jk (and Tomcat behind it) is as
follows : at the moment when the response content should be generated,

- Apache hands over the current request to mod_jk, and waits for mod_jk
to return a response.
 - mod_jk examines the request and finally returns a response which is
either "declined", "OK", or "error".
 - if the response of mod_jk was "declined", then Apache tries any
other content generator configured, ending with it's own default handler.
 - if the response of mod_jk is OK, then Apache supposes that the
content was generated by mod_jk, passes it on to the browser, and does
not call any other handler.
 - if the response was "error", then Apache breaks up the request
cycle, returns an error to the browser, and skips to logging.

True/false ?

5) Apache does not have a clue that Tomcat is behind mod_jk. For Apache,
mod_jk is "the" content handler. When Apache hands a request to mod_jk
for processing, it expects a response from mod_jk, and could not care
less if there is one, or a dozen, or zero Tomcats behind it.
True/False ?

6) What is the exact syntax of the URI's used in JkMount directives ?
I mean what is allowed/not allowed ? is it a regexp ? is it some other
form of wildcard ? is it the same bizarre kind of thing as the
<url-pattern> in the servlet specification ?
If I put for instance
JkMount /examples/* ajp13w
does the leading "/" mean "the DocumentRoot", or is this a string that
can match anywhere in the request URI ?
Can I use "^/examples/*" if I want "/examples" to be at the beginning of
the URI ?
Does there exist a description of this somewhere in the on-line
documentation ?

6) If I have this configuration section :
(assuming mod_setenvif loaded)

<Location /jk_examples>
 SetHandler jakarta-servlet
 SetEnvIf REQUEST_URI "\.(gif|jpg)$" no-jk
</Location>

is it the exact equivalent of (in the sense of does it do the same thing
as) having these directives at the server/vhost level :

 JkMount /jk_examples ajp13w
 JkMount /jk_examples/* ajp13w
 JkUnMount /jk_examples/*.gif
 JkUnMount /jk_examples/*.jpg

If not, why not ?

(I think I found the "SetHandler jakarta-servlet" somewhere in the
documentation of either Apache or Tomcat, but I think it's not at the
same place as the "JkMount/JkUnMount" documentation)


Many thanks in advance,
André

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