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Note, this guide assumes the user to have a ECMWF account.

1. Create a VM with the data flavour. This will automatically install ECMWF packages such as MARS and Aviso.

2. Configure MARS credentials, follow the instructions in Configuring MARS access. Aviso uses the same credentials.

3. Make sure to have Python3 installed with pip3 support, setuptools and wheel.

4. Install Aviso

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   language	bash
   theme	DJango

   user@local sudo pip3 install -e git+https://git.ecmwf.int/scm/lex/aviso.git@master#egg=aviso

5. Create a configuration file in the default location /etclocation ~/aviso/config.yaml with the following settings:

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   language yml
   username: <user_email> key_file: <location of ECMWF key> listeners: - event: dissemination request: destination: <user_destination> class: od expver: 1 domain: g stream: enfo step: [1,2,3] triggers: - type: echo

   The first line is required for a correct authentication, the username is the email associated to the user's ECMWF account. This can be checked by logging at https://api.ecmwf.int/v1/key/.The listeners block is an example of a dissemination event listener. request describes for which dissemination event users want to execute the triggers. It is made of a set of fields. Users have to specify only the fields they wants to use as filters. destination is a mandatory field and it is associated to one or more destinations which are linked to the user's ECMWF account. Only the notifications complying with all the fields defined will execute the trigger. The trigger in this example is echo. This will simply print out the notification to the console output.If the ECMWF key is already saved in the machine (because of a MARS installation), write it's path to key_file. Otherwise, save the ECMWF key as a file in /etc/aviso/key , this is the default location. The key can be obtained by logging at https://api.ecmwf.int/v1/key/ . 

6. Launch the aviso application

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   language bash theme DJango
   user@local aviso listen

   Once in execution this command will create a process waiting for notifications. Users can terminate the application by typing CTRL+C .

   Note, the configuration file is only read at start time, therefore every time users make changes to it they need to restart the listening process.

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from pyaviso.notification_manager import NotificationManager


# define function to be called
def do_something(notification):
    print(f"Notification for step {notification['request']['step']} received")
    # now do something useful with it ...


# define the trigger
trigger = {"type": "function", "function": do_something}

# create a event listener request that uses that trigger
request = {"class": "od", "stream": "oper", "expver": 1, "domain": "g", "step": 1}
listener = {"event": "mars", "request": request, "triggers": [trigger]}
listeners = {"listeners": [listener]}

# run it
aviso = NotificationManager()
aviso.listen(listeners=listeners)

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