portable installation of django using mod_wsgi

[pablo platt]

Hi,

I need to setup the same django project on several identical servers.
Details:
- os - free edition of oracle enterprise linux 5
- Apache / mod_wsgi
- python
- custom python2.6 installation
- oracle db with cx_Oracle

What is the simplest way to set it up?
Would you recommend creating a system user for the django project and use daemon mode?
What type of user and what privileges does it need?
Can I set ORACLE_HOME, LD_LIBRARY_PATH, PATH=$ORACLE_HOME/bin:$PATH for this user?

Would you use a virtualenv for cx_Oracle?
Can I somehow put the python2.6 inside the virtualenv so it will portable to other servers?

Thanks

[Graham Dumpleton]

On 13 April 2010 21:12, pablo platt <pablo...@gmail.com> wrote:
> Hi,
>
> I need to setup the same django project on several identical servers.
>
> Details:
> - os - free edition of oracle enterprise linux 5
> - Apache / mod_wsgi
> - python
> - custom python2.6 installation
> - oracle db with cx_Oracle
>
> What is the simplest way to set it up?

Look at buildout for doing reproducible builds.

> Would you recommend creating a system user for the django project and use
> daemon mode?

Both are good ideas.

> What type of user and what privileges does it need?

Normal user. If by privileges you mean what file system access, that
is going to depend on what your application needs to access.

At least the WSGI script file and the directories down to that
location must be accessible to Apache user. All other files need only
be accessible to the user that daemon mode process runs as.

> Can I set ORACLE_HOME, LD_LIBRARY_PATH, PATH=$ORACLE_HOME/bin:$PATH for this
> user?

Doing that would have no effect as Apache doesn't inherit them.

Ideally the .so for cx_Oracle would be built such that LD_RUN_PATH was
used to embed the library directory into the .so so that
LD_LIBRARY_PATH not needed at run time. The ORACLE_HOME then need only
be set in WSGI script file. If that isn't possible, LD_LIBRARY_PATH
may need to be set in Apache envvars file, same directory as Apache
executable. If you Linux distribution doesn't have that file, then
needs to be set in Apache startup scripts. This is assuming the Oracle
libraries not in standard library search directories for system.

> Would you use a virtualenv for cx_Oracle?

Always a good idea to use virtualenv if don't want to trust what is in
system Python site-packages. See:

http://code.google.com/p/modwsgi/wiki/VirtualEnvironments

> Can I somehow put the python2.6 inside the virtualenv so it will portable to
> other servers?

No. A virtualenv references an separate Python installation, cannot contain one.

You can use buildout however to automatically install a Python
installation just for your application setup. Apache is though bound
to that Python via mod_wsgi, so maybe buildout should install your
Apache and any other required bits as well.

Graham

[pablo platt]

Ideally the .so for cx_Oracle would be built such that LD_RUN_PATH was
used to embed the library directory into the .so so that
LD_LIBRARY_PATH not needed at run time.

I tried as you suggested but probably got the syntax wrong.
How do I use LD_LIBRARY_PATH so it'll be embedded in the .so?
$ export LD_RUN_PATH=/usr/lib/oracle/11.2/client/lib
$ python setup.py build
$ python setup.py install

The ORACLE_HOME then need only
be set in WSGI script file.

Do you mean using os.environ inside my django project .wsgi file?
does it matter where in the django.wsgi script I'm putting it?
os.environ["ORACLE_HOME"] = "/usr/lib/oracle/11.2/client"
 

If that isn't possible, LD_LIBRARY_PATH
may need to be set in Apache envvars file, same directory as Apache
executable. If you Linux distribution doesn't have that file, then
needs to be set in Apache startup scripts. This is assuming the Oracle
libraries not in standard library search directories for system.

I'm using the Apache package on the free edition of Oracle enterprise linux 5 and I don't see the envvars file
so I'll use your first suggestion.

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[Graham Dumpleton]

On 15 April 2010 10:37, pablo platt <pablo...@gmail.com> wrote:
>> Ideally the .so for cx_Oracle would be built such that LD_RUN_PATH was
>> used to embed the library directory into the .so so that
>> LD_LIBRARY_PATH not needed at run time.
>
> I tried as you suggested but probably got the syntax wrong.

Looks to be right syntax.

> How do I use LD_LIBRARY_PATH so it'll be embedded in the .so?
> $ export LD_RUN_PATH=/usr/lib/oracle/11.2/client/lib
> $ python setup.py build
> $ python setup.py install

That is what LD_RUN_PATH is for.

The difference is that LD_LIBRARY_PATH is used at run time when
invoking a program. The LD_RUN_PATH is used by linker at compile time
to embed that path in the application and/or .so file such that
LD_LIBRARY_PATH isn't needed at run time.

Did you make sure you removed the 'build' directory before building it
again in case old files still there and so didn't actually get
rebuilt?

So long as you don't have LD_LIBRARY_PATH set at the time, you can use
the 'ldd' command to list library dependencies of a .so file and see
which library directories they resolve to and whether found or not.
You can therefore use that to validate the compilation occurred
correctly and LD_RUN_PATH was used.

I believe that on a Linux box you can also use:

objdump -p blah.so

to dump out what the RPATH encoded into a .so file is as well.

>> The ORACLE_HOME then need only
>> be set in WSGI script file.
>
> Do you mean using os.environ inside my django project .wsgi file?
> does it matter where in the django.wsgi script I'm putting it?
> os.environ["ORACLE_HOME"] = "/usr/lib/oracle/11.2/client"

Before your import any modules that may cause Oracle Python wrappers
to be imported.

Graham

[pablo platt]

Thank you very much for the kind help.

To sum things for others:

1. Build and install cx_Oracle (the path may vary for xe-server/ xe-client/ instant client...)
export LD_RUN_PATH=/usr/lib/oracle/xe/app/oracle/product/10.2.0/server/lib
export ORACLE_HOME=/usr/lib/oracle/xe/app/oracle/product/10.2.0/server
rm -rf build
python setup.py build
python setup.py install

2. Add the ORACLE_HOME environment variable to yourproject/deploy/django.wsgi file:
os.environ["ORACLE_HOME"] = "/usr/lib/oracle/xe/app/oracle/product/10.2.0/server"

3. When using cx_Oracle from the shell, for example in order to use django syncdb:
export ORACLE_HOME=/usr/lib/oracle/xe/app/oracle/product/10.2.0/server
export LD_LIBRARY_PATH=$ORACLE_HOME/lib
export PATH=$ORACLE_HOME/bin:$PATH
python manage.py runserver

[Graham Dumpleton]

On 16 April 2010 03:23, pablo platt <pablo...@gmail.com> wrote:
> Thank you very much for the kind help.
>
> To sum things for others:
>
> 1. Build and install cx_Oracle (the path may vary for xe-server/ xe-client/
> instant client...)
> export LD_RUN_PATH=/usr/lib/oracle/xe/app/oracle/product/10.2.0/server/lib
> export ORACLE_HOME=/usr/lib/oracle/xe/app/oracle/product/10.2.0/server
> rm -rf build
> python setup.py build
> python setup.py install
>
> 2. Add the ORACLE_HOME environment variable to
> yourproject/deploy/django.wsgi file:
> os.environ["ORACLE_HOME"] =
> "/usr/lib/oracle/xe/app/oracle/product/10.2.0/server"
>
> 3. When using cx_Oracle from the shell, for example in order to use django
> syncdb:
> export ORACLE_HOME=/usr/lib/oracle/xe/app/oracle/product/10.2.0/server
> export LD_LIBRARY_PATH=$ORACLE_HOME/lib

Having done the LD_RUN_PATH at compile time, you shouldn't need the
LD_LIBRARY_PATH at run time. At least not for the cx_Oracle module
when running Python. You might still need it for command line Oracle
programs like sqlplus.

Graham