.. _server_deployment:

**************************
`Server Deployment`:index:
**************************

pgAdmin may be deployed as a web application by configuring the app to run in
server mode and then deploying it either behind a webserver running as a reverse
proxy, or using the WSGI interface.

When deployed in server mode, there are two notable differences for users:

* Users must login before they can use pgAdmin. An initial superuser account
  is created when server mode is initialised, and this user can add additional
  superusers and non-superusers as required.
* File storage is restricted to a virtual root directory for each individual
  user under the directory configured using the ``STORAGE_DIR`` configuration
  parameter. Users do not have access to the complete filesystem of the server.

The following instructions demonstrate how pgAdmin may be run as a WSGI 
application under ``Apache HTTPD``, using ``mod_wsgi``, standalone using ``uWSGI``
or ``Gunicorn``, or under ``NGINX`` using using ``uWSGI`` or ``Gunicorn``.


.. seealso:: For detailed instructions on building and configuring pgAdmin from
    scratch, please see the README file in the top level directory of the source code.
    For convenience, you can find the latest version of the file
    `here <https://github.com/pgadmin-org/pgadmin4/blob/master/README.md>`_,
    but be aware that this may differ from the version included with the source code
    for a specific version of pgAdmin.

Requirements
************

**Important**: Some components of pgAdmin require the ability to maintain affinity
between client sessions and a specific database connection (for example, the 
Query Tool in which the user might run a BEGIN command followed by a number of
DML SQL statements, and then a COMMIT). pgAdmin has been designed with built-in
connection management to handle this, however it requires that only a single
Python process is used because it is not easily possible to maintain affinity
between a client session and one of multiple WSGI worker processes.

On Windows systems, the Apache HTTP server uses a single process, multi-threaded
architecture. WSGI applications run in ``embedded`` mode, which means that only
a single process will be present on this platform in all cases.

On Unix systems, the Apache HTTP server typically uses a multi-process, single
threaded architecture (this is dependent on the ``MPM`` that is chosen at 
compile time). If ``embedded`` mode is chosen for the WSGI application, then
there will be one Python environment for each Apache process, each with it's own
connection manager which will lead to loss of connection affinity. Therefore
one should use ``mod_wsgi``'s ``daemon`` mode, configured to use a single
process. This will launch a single instance of the WSGI application which is 
utilised by all the Apache worker processes.

Whilst it is true that this is a potential performance bottleneck, in reality
pgAdmin is not a web application that's ever likely to see heavy traffic 
unlike a busy website, so in practice should not be an issue.

Future versions of pgAdmin may introduce a shared connection manager process to
overcome this limitation, however that is a significant amount of work for 
little practical gain.

Configuration
*************

In order to configure pgAdmin to run in server mode, it may be necessary to
configure the Python code to run in multi-user mode, and then to configure the
web server to find and execute the code.

See :ref:`config_py` for more information on configuration settings.

Python
------

From pgAdmin 4 v2 onwards, server mode is the default configuration. If running under
the desktop runtime, this is overridden automatically. There should typically be no
need to modify the configuration simply to enable server mode to work, however it may
be desirable to adjust some of the paths used.

In order to configure the Python code, follow these steps:

1. Create a ``config_local.py`` file alongside the existing ``config.py`` file.

2. Edit ``config_local.py`` and add the following settings. In most cases, the default
   file locations should be appropriate:

   *NOTE: You must ensure the directories specified are writeable by
   the user that the web server processes will be running as, e.g. apache or www-data.
   You may specify DATA_DIR in order to create all required directories and files
   under DATA_DIR folder.*

   .. code-block:: python

       LOG_FILE = '/var/log/pgadmin4/pgadmin4.log'
       SQLITE_PATH = '/var/lib/pgadmin4/pgadmin4.db'
       SESSION_DB_PATH = '/var/lib/pgadmin4/sessions'
       STORAGE_DIR = '/var/lib/pgadmin4/storage'
       AZURE_CREDENTIAL_CACHE_DIR = '/var/lib/pgadmin4/azurecredentialcache'
       KERBEROS_CCACHE_DIR = '/var/lib/pgadmin4/kerberoscache'

4. Run the following command to create the configuration database:

   .. code-block:: bash

       # python setup.py setup-db

5. Change the ownership of the configuration database to the user that the web server
   processes will run as, for example, assuming that the web server runs as user
   www-data in group www-data, and that the SQLite path is ``/var/lib/pgadmin4/pgadmin4.db``:

   .. code-block:: bash

       # chown www-data:www-data /var/lib/pgadmin4/pgadmin4.db

Hosting
*******

There are many possible ways to host pgAdmin in server mode. Some examples are
given below:

Apache HTTPD Configuration (Windows)
------------------------------------

Once Apache HTTP has been configured to support ``mod_wsgi``, the pgAdmin
application may be configured similarly to the example below:

.. code-block:: apache

    <VirtualHost *>
        ServerName pgadmin.example.com
        WSGIScriptAlias / "C:\Program Files\pgAdmin4\web\pgAdmin4.wsgi"
        <Directory "C:\Program Files\pgAdmin4\web">
                Order deny,allow
                Allow from all
        </Directory>
    </VirtualHost>

Now open the file ``C:\Program Files\pgAdmin4\web\pgAdmin4.wsgi`` with your favorite editor and add the code
below which will activate Python virtual environment when Apache server runs.

.. code-block:: python

    activate_this = 'C:\Program Files\pgAdmin4\venv\Scripts\activate_this.py'
    exec(open(activate_this).read())

**Note:** The changes made in ``pgAdmin4.wsgi`` file will revert when pgAdmin4 is either upgraded or downgraded.
    
Apache HTTPD Configuration (Linux/Unix)
---------------------------------------

Once Apache HTTP has been configured to support ``mod_wsgi``, the pgAdmin
application may be configured similarly to the example below:

.. code-block:: apache

    <VirtualHost *>
        ServerName pgadmin.example.com

        WSGIDaemonProcess pgadmin processes=1 threads=25 python-home=/path/to/python/virtualenv
        WSGIScriptAlias / /opt/pgAdmin4/web/pgAdmin4.wsgi

        <Directory /opt/pgAdmin4/web>
            WSGIProcessGroup pgadmin
            WSGIApplicationGroup %{GLOBAL}
            Order deny,allow
            Allow from all
        </Directory>
    </VirtualHost>

**Note:** If you're using Apache HTTPD 2.4 or later, replace the lines:

.. code-block:: apache

            Order deny,allow
            Allow from all

with:

.. code-block:: apache

            Require all granted

Adjust as needed to suit your access control requirements.

Standalone Gunicorn Configuration
---------------------------------

pgAdmin may be hosted by Gunicorn directly simply by running a command such as
the one shown below. Note that this example assumes pgAdmin was installed using
the Python Wheel (you may need to adjust the path to suit your installation):

.. code-block:: bash

    gunicorn  --bind 0.0.0.0:80 \
              --workers=1 \
              --threads=25 \
              --chdir /usr/lib/python3.7/dist-packages/pgadmin4 \
              pgAdmin4:app

Standalone uWSGI Configuration
------------------------------

pgAdmin may be hosted by uWSGI directly simply by running a command such as
the one shown below. Note that this example assumes pgAdmin was installed using
the Python Wheel (you may need to adjust the path to suit your installation):

.. code-block:: bash

    uwsgi --http-socket 0.0.0.0:80 \
          --processes 1 \
          --threads 25 \
          --chdir /usr/lib/python3.7/dist-packages/pgadmin4/ \
          --mount /=pgAdmin4:app

NGINX Configuration with Gunicorn
---------------------------------

pgAdmin can be hosted by Gunicorn, with NGINX in front of it. Note that these
examples assume pgAdmin was installed using the Python Wheel (you may need to
adjust the path to suit your installation).

To run with pgAdmin in the root directory of the server, start Gunicorn using a
command similar to:

.. code-block:: bash

    gunicorn --bind unix:/tmp/pgadmin4.sock \
             --workers=1 \
             --threads=25 \
             --chdir /usr/lib/python3.7/dist-packages/pgadmin4 \
             pgAdmin4:app

And configure NGINX:

.. code-block:: nginx

    location / {
        include proxy_params;
        proxy_pass http://unix:/tmp/pgadmin4.sock;
    }

Alternatively, pgAdmin can be hosted in a sub-directory (/pgadmin4 in this case)
on the server. Start Gunicorn as when using the root directory, but configure
NGINX as follows:

.. code-block:: nginx

    location /pgadmin4/ {
        include proxy_params;
        proxy_pass http://unix:/tmp/pgadmin4.sock;
        proxy_set_header X-Script-Name /pgadmin4;
    }

NGINX Configuration with uWSGI
------------------------------

pgAdmin can be hosted by uWSGI, with NGINX in front of it. Note that these
examples assume pgAdmin was installed using the Python Wheel (you may need to
adjust the path to suit your installation).

To run with pgAdmin in the root directory of the server, start uWSGI using a
command similar to:

.. code-block:: bash

    uwsgi --socket /tmp/pgadmin4.sock \
          --processes 1 \
          --threads 25 \
          --chdir /usr/lib/python3.7/dist-packages/pgadmin4/ \
          --manage-script-name \
          --mount /=pgAdmin4:app

And configure NGINX:

.. code-block:: nginx

    location / { try_files $uri @pgadmin4; }
    location @pgadmin4 {
        include uwsgi_params;
        uwsgi_pass unix:/tmp/pgadmin4.sock;
    }

Alternatively, pgAdmin can be hosted in a sub-directory (/pgadmin4 in this case)
on the server. Start uWSGI, noting that the directory name is specified in the
``mount`` parameter:

.. code-block:: bash

    uwsgi --socket /tmp/pgadmin4.sock \
          --processes 1 \
          --threads 25 \
          --chdir /usr/lib/python3.7/dist-packages/pgadmin4/ \
          --manage-script-name \
          --mount /pgadmin4=pgAdmin4:app

Then, configure NGINX:

.. code-block:: nginx

    location = /pgadmin4 { rewrite ^ /pgadmin4/; }
    location /pgadmin4 { try_files $uri @pgadmin4; }
    location @pgadmin4 {
      include uwsgi_params;
      uwsgi_pass unix:/tmp/pgadmin4.sock;
    }

Additional Information
----------------------

.. note:: pgAdmin will spawn additional Python processes from time to time, and
    relies on the *sys.executable* variable in Python to do this. In some cases,
    you may need to override that value to ensure the correct interpreter is
    used, instead of the WSGI host process. For example, uWSGI offers the
    *--py-sys-executable* command line option to achieve this.
