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Dirt Cheap Oracle step #5(b) of 6: Making Apache and EPG Play Together

September 24, 2007

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I want people to get to both my Apache web server (port 8000) as well as Apex (port 8080) via the default HTTP port (80) through the router, but you can’t map one port to two ports – otherwise, how is the router to know which port to pass requests on to? There’s a good reason why I’ve chosen the web server to get all the traffic, and that’s because I have an idea how to get Apache to pass traffic to Apex, but not how the other way around could be done (EPG pass traffic to Apache).

This was a bit of a conundrum, and I was forced to do some spelunking in the documentation for Apache web server configuration. Reading these docs is highly recommended, it’s a lot of fun although at first it’s hard to know where to start. I’d recommend starting with the sections on Configuration Files and Configuration Sections, with a bit of browsing through the various commands, and then maybe the URL Rewriting Guide.

It wasn’t pretty; in the end it came down to one of two options:
(a) Redirect
(b) Rewrite

I can’t use redirection because whenever someone goes to my web page, redirection means Apache will send back a message saying “wrong address, please try this new address” which would include port 8080, which for at least one friend of mine would be blocked.

So I tried URL rewriting, adding the following lines into my /etc/httpd/conf/httpd.conf:

<Location /apex>    RewriteEngine On    RewriteRule (.*) http://%{SERVER_NAME}:8080%{REQUEST_URI} [last]    Order deny,allow    Deny from none    Allow from all</Location>

(BTW if you’re wondering, the third line starting with “RewriteRule” is one long line, “{REQUEST_URI}…” should appear directly after “…8080%” without any line break)

This means: for any URL requesting /apex or anything under that folder, rewrite the request to go to the same server and address, but on port 8080.

This would have worked, except that according to the documentation, if the rewrite engine changes the host or port of the url, it will actually do a Redirect! So rewriting is no better than redirection for this case.

In the end, I found a third option:
(c) ProxyPass

I added the following lines into httpd.conf:

ProxyRequests OffProxyPass /apex http://localhost:8080/apexProxyPassReverse / http://localhost:8080ProxyReceiveBufferSize 49152

(the above assumes that localhost is mapped in my hosts file)

This solved the problem for me. What the lines above mean is, any request for /apex or anything underneath it is internally passed on to http://localhost:8080/apex which will act like a proxy server for the request. This operation is transparent to the client, which doesn’t know that anything’s changed. I believe ProxyPassReverse is also needed so that requests going back from port 8080 is routed in the reverse direction; not entirely sure how that works but at least it works.

Now, that works, but when I access Apex pages via port 8000 (80 from the outside), I get all the text but no images. That’s because Apex was serving images via /i/ on port 8080 (via EPG), but now we have this proxy thing only passing requests for /apex/* to it, and Apache web server can’t find /i/.

At first I tried adding another ProxyPass line for /i to port 8080, and this did work; however, all the pages loaded very slowly, all the images were visibly taking time to load each time a page was refreshed, so no images were being cached. I figured this lack of caching was because Apache can’t tell that an image hasn’t been changed since the last time it was requested.

This performance problem was solved by getting all the Apex images and putting them on another folder on the Linux box (e.g. /usr/lib/oracle/apex/images) and adding the following line to httpd.conf:

Alias /i/ "/usr/lib/oracle/apex/images/"

This means that all the Apex images are now served by Apache web server instead of by Apex. It also means that application images I’ve loaded have to be copied out to the file system, but in my case there weren’t many and it didn’t take long.

It’s all very simple, isn’t it? Not. But at least it works, and reasonably well. My friends and family are suitably impressed, although they have no inkling of the trouble I went to to get it all working. Ah, the thankless life of an Oracle programmer – but it’s all worth it in the end when I can do full-on development remotely, wherever in the world I happen to be (e.g. down the road at a friend’s place).

Next problem: world peace. Or, migrating my existing Apex applications from the XP box to Linux. Depending on how much time I have.

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