Use Flask-APScheduler. Move docker swarm logic to scheduler.

app/__init__.py

 from config import config
 from flask import Flask
+from flask_apscheduler import APScheduler
 from flask_login import LoginManager
 from flask_mail import Mail
 from flask_sqlalchemy import SQLAlchemy
-from .scheduler import Scheduler
-from .swarm import Swarm
+
 
 db = SQLAlchemy()
 login_manager = LoginManager()
 login_manager.login_view = 'auth.login'
 mail = Mail()
-scheduler = Scheduler()
-swarm = Swarm()
+scheduler = APScheduler()
 
 
 def create_app(config_name):
     app = Flask(__name__)
     app.config.from_object(config[config_name])
-    config[config_name].init_app(app)
 
+    config[config_name].init_app(app)
     db.init_app(app)
     login_manager.init_app(app)
     mail.init_app(app)
     scheduler.init_app(app)
-    swarm.init_app(app)
+    scheduler.start()
 
     from .auth import auth as auth_blueprint
     app.register_blueprint(auth_blueprint, url_prefix='/auth')
@@ -35,3 +34,13 @@ def create_app(config_name):
     app.register_blueprint(main_blueprint)
 
     return app
+
+
+def create_minimal_app(config_name):
+    app = Flask(__name__)
+    app.config.from_object(config[config_name])
+
+    config[config_name].init_app(app)
+    db.init_app(app)
+
+    return app

app/scheduler.py

-from apscheduler.schedulers.background import BackgroundScheduler
-from datetime import datetime
-from sqlalchemy import create_engine
-from sqlalchemy.orm import scoped_session, sessionmaker
-import os
-
-
-class Scheduler(BackgroundScheduler):
-    def __init__(self, app=None):
-        super().__init__()
-        self.app = app
-        if app is not None:
-            self.init_app(app)
-
-    def init_app(self, app):
-        engine = create_engine(app.config['SQLALCHEMY_DATABASE_URI'])
-        self.Session = scoped_session(sessionmaker(bind=engine))
-        if not app.debug or os.environ.get('WERKZEUG_RUN_MAIN') == 'true':
-            self.add_job(self.check_jobs, id='jobs', seconds=10, trigger='interval')
-            self.start()
-
-    def check_jobs(self):
-        from .models import Job
-        from . import swarm
-
-        session = self.Session()
-        jobs = session.query(Job)
-        submitted_jobs = jobs.filter_by(status='submitted').all()
-        foo_jobs = jobs.filter(Job.status != 'complete',
-                               Job.status != 'failed',
-                               Job.status != 'submitted').all()
-        for job in submitted_jobs:
-            swarm.run(job)
-            job.status = 'scheduled'
-        for job in foo_jobs:
-            '''
-            ' TODO: Handle service not found error.
-            '''
-            service = swarm.docker.services.get(str(job.id))
-            job.status = service.tasks()[0].get('Status').get('State')
-            if job.status == 'complete' or job.status == 'failed':
-                job.end_date = datetime.utcnow()
-                service.remove()
-        session.commit()
-        self.Session.remove()

app/swarm.py → app/scheduler_functions.py

+from datetime import datetime
+from . import create_minimal_app, db
+from .models import Job
 import docker
 import json
 import os
 
 
-class Swarm:
-    def __init__(self, app=None):
-        self.app = app
-        if app is not None:
-            self.init_app(app)
-        self.docker = docker.from_env()
-
-    def init_app(self, app):
-        pass
-
-    '''
-    ' Swarm mode is intendet to run containers which serve a non terminating
-    ' service like a webserver. For processing an occuring job it is necessary
-    ' to use an one-shot container, which stops after the wrapped job process
-    ' is completly executed. In order to run these one-shot containers in Swarm
-    ' mode, the following run method is implemented analog to the presented
-    ' implementation in Alex Ellis' blog post "One-shot containers on Docker
-    ' Swarm"¹.
-    '
-    ' ¹ https://blog.alexellis.io/containers-on-swarm/
-    '''
-
-    def run(self, job):
-        '''
-        Input is a job.
-        '''
-        # Prepare argument values needed for the service creation.
-        service_args = json.loads(job.service_args)
+def check_jobs():
+    app = create_minimal_app(os.getenv('FLASK_CONFIG') or 'default')
+    app.app_context().push()
+    docker_client = docker.from_env()
+    jobs = db.session.query(Job)
+    submitted_jobs = jobs.filter_by(status='submitted').all()
+    foo_jobs = jobs.filter(Job.status != 'complete',
+                           Job.status != 'failed',
+                           Job.status != 'submitted').all()
+    for job in submitted_jobs:
         _command = (job.service
                     + ' -i /files'
                     + ' -o /files/output'
-                    + ' ' + ' '.join(service_args))
+                    + ' ' + ' '.join(json.loads(job.service_args)))
         _constraints = ['node.role==worker']
         _image = 'gitlab.ub.uni-bielefeld.de:4567/sfb1288inf/{}:{}'.format(
             job.service,
@@ -74,7 +59,7 @@ class Swarm:
         '       (name=_name). Because there is no id generator for now, it is
         '       not set, so that the Docker engine assigns a random name.
         '''
-        service = self.docker.services.create(
+        service = docker_client.services.create(
             _image,
             command=_command,
             constraints=_constraints,
@@ -84,5 +69,14 @@ class Swarm:
             resources=_resources,
             restart_policy=_restart_policy
         )
-
-        return service
+        job.status = 'scheduled'
+    for job in foo_jobs:
+        '''
+        ' TODO: Handle service not found error.
+        '''
+        service = docker_client.services.get(str(job.id))
+        job.status = service.tasks()[0].get('Status').get('State')
+        if job.status == 'complete' or job.status == 'failed':
+            job.end_date = datetime.utcnow()
+            service.remove()
+    db.session.commit()

app/services/views.py

@@ -3,9 +3,7 @@ from . import services
 from flask_login import current_user, login_required
 from .forms import NewOCRJobForm, NewNLPJobForm
 from ..models import Job
-from ..import swarm
 from .. import db
-from threading import Thread
 import json
 import os
 

config.py

@@ -5,6 +5,14 @@ basedir = os.path.abspath(os.path.dirname(__file__))
 
 
 class Config:
+    JOBS = [
+        {
+            'id': 'check_jobs',
+            'func': 'app.scheduler_functions:check_jobs',
+            'seconds': 3,
+            'trigger': 'interval'
+        }
+    ]
     MAIL_SERVER = os.environ.get('MAIL_SERVER', 'smtp.gmail.com')
     MAIL_PORT = int(os.environ.get('MAIL_PORT', '587'))
     MAIL_USE_TLS = os.environ.get('MAIL_USE_TLS', 'true').lower() in \

requirements.txt

-APScheduler==3.6.1 
 docker==4.0.2
 Flask==1.0.3
+Flask-APScheduler==1.11.0
 Flask-Login==0.4.1
 Flask-Mail==0.9.1
 Flask-Migrate==2.5.2