Managing external daemons/services
==================================

uWSGI can easily monitor external processes, allowing you to increase
reliability and usability of your multi-tier apps.  For example you can manage
services like Memcached, Redis, Celery, Ruby delayed_job or even dedicated
PostgreSQL instances.

Kinds of services
*****************

Currently uWSGI supports 3 categories of processes:

* ``--attach-daemon`` -- directly attached non daemonized processes
* ``--smart-attach-daemon`` -- pidfile governed (both foreground and daemonized)
* ``--smart-attach-daemon2`` -- pidfile governed with daemonization management

The first category allows you to directly attach processes to the uWSGI master.
When the master dies or is reloaded these processes are destroyed. This is the
best choice for services that must be flushed whenever the app is restarted.

Pidfile governed processes can survive death or reload of the master so long as
their pidfiles are available and the pid contained therein matches a running
pid. This is the best choice for processes requiring longer persistence, and
for which a brutal kill could mean loss of data such as a database.

The last category is a superset of the second one. If your process does not
support daemonization or writing to pidfile, you can let the master do the
management.  Very few daemons/applications require this feature, but it could
be useful for tiny prototype applications or simply poorly designed ones.

Since uWSGI 2.0 a fourth option, ``--attach-daemon2`` has been added for advanced configurations (see below).

Examples
********

Managing a **memcached** instance in 'dumb' mode. Whenever uWSGI is stopped or reloaded, memcached is destroyed.

.. code-block:: ini

   [uwsgi]
   master = true
   socket = :3031
   attach-daemon = memcached -p 11311 -u roberto

Managing a **memcached** instance in 'smart' mode. Memcached survives uWSGI stop and reload.

.. code-block:: ini

   [uwsgi]
   master = true
   socket = :3031
   smart-attach-daemon = /tmp/memcached.pid memcached -p 11311 -d -P /tmp/memcached.pid -u roberto

Managing 2 **mongodb** instances in smart mode:

.. code-block:: ini

   [uwsgi]
   master = true
   socket = :3031
   smart-attach-daemon = /tmp/mongo1.pid mongod --pidfilepath /tmp/mongo1.pid --dbpath foo1 --port 50001
   smart-attach-daemon = /tmp/mongo2.pid mongod --pidfilepath /tmp/mongo2.pid --dbpath foo2 --port 50002

Managing **PostgreSQL** dedicated-instance (cluster in /db/foobar1):

.. code-block:: ini

   [uwsgi]
   master = true
   socket = :3031
   smart-attach-daemon = /db/foobar1/postmaster.pid /usr/lib/postgresql/9.1/bin/postgres -D /db/foobar1

Managing **celery**:

.. code-block:: ini

   [uwsgi]
   master = true
   socket = :3031
   smart-attach-daemon = /tmp/celery.pid celery -A tasks worker --pidfile=/tmp/celery.pid

Managing **delayed_job**:

.. code-block:: ini

   [uwsgi]
   master = true
   socket = :3031
   env = RAILS_ENV=production
   rbrequire = bundler/setup
   rack = config.ru
   chdir = /var/apps/foobar
   smart-attach-daemon = %(chdir)/tmp/pids/delayed_job.pid %(chdir)/script/delayed_job start

Managing **dropbear**:


.. code-block:: ini

   [uwsgi]
   namespace = /ns/001/:testns
   namespace-keep-mount = /dev/pts
   socket = :3031
   exec-as-root = chown -R www-data /etc/dropbear
   attach-daemon = /usr/sbin/dropbear -j -k -p 1022 -E -F -I 300

When using the namespace option you can attach a dropbear daemon to allow direct
access to the system inside the specified namespace.  This requires the
*/dev/pts* filesystem to be mounted inside the namespace, and the user your
workers will be running as have access to the */etc/dropbear* directory inside
the namespace.

Legion support
**************

Starting with uWSGI 1.9.9 it's possible to use the :doc:`Legion` subsystem for
daemon management.  Legion daemons will be executed only on the legion
lord node, so there will always be a single daemon instance running in each
legion. Once the lord dies a daemon will be spawned on another node.  To add a
legion daemon use --legion-attach-daemon, --legion-smart-attach-daemon and
--legion-smart-attach-daemon2 options, they have the same syntax as normal
daemon options. The difference is the need to add legion name as first
argument.

Example:

Managing **celery beat**:

.. code-block:: ini

   [uwsgi]
   master = true
   socket = :3031
   legion-mcast = mylegion 225.1.1.1:9191 90 bf-cbc:mysecret
   legion-smart-attach-daemon = mylegion /tmp/celery-beat.pid celery beat --pidfile=/tmp/celery-beat.pid
   
   
``--attach-daemon2``
****************

This option has been added in uWSGI 2.0 and allows advanced configurations. It is a keyval option, and it accepts the following keys:

* ``command``/``cmd``/``exec``: the command line to execute
* ``freq``: maximum attempts before considering a daemon "broken"
* ``pidfile``: the pidfile to check (enable smart mode)
* ``control``: if set, the daemon becomes a 'control' one: if it dies the whole uWSGI instance dies
* ``daemonize``/``daemon``: daemonize the process (enable smart2 mode)
* ``touch`` semicolon separated list of files to check: whenever they are 'touched', the daemon is restarted
* ``stopsignal``/``stop_signal``: the signal number to send to the daemon when uWSGI is stopped
* ``reloadsignal``/``reload_signal``: the signal to send to the daemon when uWSGI is reloaded
* ``stdin``: if set the file descriptor zero is not remapped to /dev/null
* ``uid``: drop privileges to the specified uid (requires master running as root)
* ``gid``: drop privileges to the specified gid (requires master running as root)
* ``ns_pid``: spawn the process in a new pid namespace (requires master running as root, Linux only)
* ``chdir``: chdir() to the specified directory before running the command (added in uWSGI 2.0.6)

Example:

.. code-block:: ini

   [uwsgi]
   attach-daemon2 = cmd=my_daemon.sh,pidfile=/tmp/my.pid,uid=33,gid=33,stopsignal=3

