Quick Start

Aviso can be used as a Python API or as Command-Line Interface (CLI) application. Here a few steps to quickly get a working configuration listening to notifications.

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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. Create a configuration file in the default location ~/aviso/config.yaml.

   1. Below an example for products notifications:

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      listeners: - event: dissemination request: destination: <user_destination> class: od expver: 1 domain: g stream: enfo step: [1,2,3] triggers: - type: echo

      Note the 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.

   2. Below an example for real time model output notifications:

      Code Block
      language yml
      listeners: - event: mars request: class: od expver: 1 domain: g stream: enfo step: [1,2,3] triggers: - type: echo

      Note the mars event listener. destination field is not present here.

4. Activate base conda environment. Aviso is part of it.

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   user@local conda activate

   
   

5. Launch the aviso application

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   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.

Testing my listener

Aviso provides the capability of submitting test notifications to a local server. This functionality can be used to test the listener configuration without any impact to the operational server.

1. Launch the aviso application in test mode. This allows to connect to a local file-based notification server, part of the aviso application, that is able to simulate the notification server behaviour.

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   language bash theme DJango
   user@local aviso listen --test

   The console should display a Test Mode message.

2. Send a test dissemination notification. From another terminal run the notify command. Here an example, matching the example configuration presented above:

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   language bash theme DJango
   user@local aviso notify event=dissemination,class=od,date=20190810,destination=<user_destination>,domain=g,expver=1,step=1,stream=enfo,time=0,location=xxxx --test

   Note the list of fields required for a dissemination event, the order is not important, but the command requires all of them. The destination has to match the one of the listener configuration.

   Note, to submit a test mars notification the fields destination and location have to be removed.

3. After a few seconds, the console output should display the notification, as the trigger is set to echo. 

Defining my listener

Aviso configuration file allows the definition of multiple listeners. Alternatively, the listeners configuration can be indicated as an independent file or multiple files:

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• an event type
• a request block
• a triggers block

Event

Aviso offers notifications for the following types of events:

• The dissemination event is submitted by the product generation. The related listener configuration must define the destination field. A notification related to a dissemination event will have the field location containing the URL to the product notified.

• The mars event is designed for real-time data from the model output. The related listener configuration does not have the destination field and has no mandatory fields. Moreover the related notification will not contain the location field because users will have to access to it by the conventional MARS API.

Request

The table below shows the full list of fields accepted in a request block. These fields represent a subset on the MARS language.

Triggers

The triggers block accepts a sequence of triggers. Each trigger will result in an independent process executed every time a notification is received. This sections shows the type of triggers currently available.

Echo

This is the simplest trigger as it prints the notification to the console output. It is used for testing and it does not accept any extra parameters.

triggers:
  - type: echo

Log

This trigger logs the event to a log file. It is useful for recording the received event. Note, it will fail if the directory does not exist.

triggers:
  - type: log
    path: testLog.log

Command

This trigger allows the user to define a shell command to work with the notification.

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Here an example file of a listener command triggering a bash script executing a MARS request.

Aviso as a Python API

Aviso can be used as a Python API. This is intended for users that want to integrate Aviso in a bigger workflow written in Python or that simply have their trigger defined as a Python function. Below an example of a python script that defines a function to be executed once a notification is received, creates a listener that references to this function trigger and finally passes it to aviso to execute.

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Here an example file of a Python script running Aviso and executing a MARS request after a notification is received.

Dealing with historical  notifications

Before listening to new notifications, Aviso by default checks what was the last notification received and it will then return all the notifications that have been missed since. It will then carry on by listening to new ones. The first ever time the application runs however no previous notification will be returned. This behaviour allows users not to miss any notifications in case of machine reboots.

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In absence of --to, the system after having retrieved the past notifications, it ​will continue listening to future notifications. If --to is defined Aviso will terminate once retrieved all the past notifications.

Running as a service

Aviso can be executed as a system service. This helps automating its restart in case of machine reboots. The following steps help to configure Aviso to run as a service that automatically restart:

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