Implement an Arguments Key Handling for Entry Points Defined in snap-openstack.yaml

[Dmitrii Shcherbakov]

Right now it is only possible to pass additional arguments to an app via a top-level snapcraft.yaml file, for example, ceilometer's agent-central service uses ceilometer-polling script and passes --polling-namespaces argument to it so we need to do the same in the app definition. The following can be used to do it:

https://paste.ubuntu.com/23786868/

  agent-central:
    command: snap-openstack ceilometer-polling --polling-namespaces central

It seems to be cleaner to do it in the snap/snap-openstack.yaml though:

1) like this https://paste.ubuntu.com/23786827/
2) or via key-value pairs:

    arguments:
      polling-namespaces: central

The code in question is here https://git.launchpad.net/snap.openstack/tree/snap_openstack/base.py#n128

we just need to add a handler for the arguments key.

[Corey Bryant (corey.bryant)]

While we could get away with specifying the arguments in snapcraft.yaml, I agree that it would be cleaner to specify additional arguments in snap-openstack.yaml, alongside other args that are currently passed to the daemon (ie. log files, config files).

[Dmitrii Shcherbakov (dmitriis)]

Found another reason for this to be implemented:

1) ceilometer API requires --port option to be present
ubuntu@juju-180ad0-oct-2x-next-0:~/src/ceilometer-6.1.3$ systemctl cat ceilometer-api.service

# /lib/systemd/system/ceilometer-api.service
[Unit]
Description=Ceilometer API
After=mongodb.service rabbitmq-server.service

[Service]
...
Environment=PORT=8777
...
ExecStart=/usr/bin/ceilometer-api --port ${PORT} -- --config-file=/etc/ceilometer/ceilometer.conf --log-file=/var/log/ceilometer/ceilometer-api.log
...

# /etc/systemd/system/ceilometer-api.service.d/override.conf
[Service]
Environment=PORT=8767

2) Looking at how it is launched I can see that the common options such as --log-file, --config-file or --config-dir are passed after the port is specified with two dashes in between:

/usr/bin/ceilometer-api -h
usage: ceilometer-api [-h] [--port PORT] -- [passed options]

positional arguments:
  -- [passed options] '--' is the separator of the arguments used to start
                        the WSGI server and the arguments passed to the WSGI
                        application.

optional arguments:
  -h, --help show this help message and exit
  --port PORT, -p PORT TCP port to listen on (default: 8000)

As here:

ubuntu@juju-180ad0-oct-2x-next-0:~/src/ceilometer-6.1.3$ systemctl status ceilometer-api.service | grep -ioP '\d+.*?/usr/bin/ceilometer-api.*?$'
26777 /usr/bin/python /usr/bin/ceilometer-api --port 8767 -- --config-file=/etc/ceilometer/ceilometer.conf --log-file=/var/log/ceilometer/ceilometer-api.log

Using snapcraft.yaml for passing the port parameter results in the argument reordering:

snapcraft.yaml:
...
apps:
  api:
    command: snap-openstack ceilometer-api --port 8767 --
...

янв 13 12:09:21 maas-xenial1 snap[15278]: WARNING:snap_openstack.base:Configuration file /var/snap/ceilometer/common/etc/ceilometer/ceilometer.conf not found, skipping
янв 13 12:09:25 maas-xenial1 snap[15278]: usage: ceilometer-api [-h] [--port PORT] -- [passed options]
янв 13 12:09:25 maas-xenial1 snap[15278]: ceilometer-api: error: unrecognized arguments: --config-file=/snap/ceilometer/x1/etc/ceilometer/ceilometer.conf --config-dir=/var/snap/ceilometer/common/etc/ceilometer.conf.d --log-file=/var/snap/ceilometer/common/log/ceilometer-api.log

So special handling is required here to correctly launch a service using snap.openstack helper code.

In case of ceilometer this is the only service that requires special handling btw.

[James Page (james-page)]

ceilometer-api needs to be snapped as a wsgi process, using uwsgi as we did in the keystone snap - the ceilometer-api standalone binary is deprecated for removal and does not scale in any way.

[Dmitrii Shcherbakov (dmitriis)]

James,

Thanks, I did it and uploaded the result to my repo until we are ready to create an official one:
https://github.com/dshcherb/snap-ceilometer