Creating Your Own service¶

This tutorial will continue from where Deploying Your First Service left off. There we created a basic service using the mvi init command.

>>> mvi init 
project_name [my_project]: my_first_mvi_project

And this created three files and two directories.

>>> ls ./my_first_mvi_project -a 
.  ..  .s2i/  README.md  requirements.txt  service.py  tests/

Where service.py contains the service source code. Let’s look at how a typical service.py file might look.

Setup¶

As usual, the first step is to import packages. We also initialize a logger so we can get information about our services for debugging:

import logging
from mvi import service
from mvi.communication import Severity, notify

logger = logging.getLogger(__name__)

Only service is actually required, but we recommend to import and use the standard python logging package. notify() and Severity in the mvi.communication module are used for the notification functionality in MVI.

If any external packages are used, they must be specified in the requirements.txt file. That way they will be installed the service is deployed.

Note

It is highly recommended to pin your requirements to specific versions when in a production environment, for example numpy==1.19.4

The service object helps us set up entrypoints for the service, add parameters and start the service. The logger is just a regular python logging object, which MVI natively supports. The logs from a service can be read from the dashboard or using mvi logs <name> <version>.

Defining parameters¶

It is possible to define parameters that automatically get exposed to the API and can be freely changed from outside a running service

service.add_parameter("greeting_phrase", "Hello")

To use the parameter in the code you do

greeting_phrase = service.get_parameter("greeting_phrase")

This way you can control the behaviour of your running services without having to make any code changes. We recommend using this for e.g. tuning parameters.

These parameters can be changed via the docs of the service, see API Autodocs for how to do it. Another way to change these parameters is by sending HTTP POST requests directly, for instance via pythons requests library.

Example of changing the greeting_phrase parameter for this service:

json_data = {"greeting_phrase": "Bonjour"}

response = requests.post(
    "http:://<host>/services/<my_service>/parameters/greeting_phrase",
    json=json_data,
    headers={"Authorization": f"Bearer {TOKEN}"})

Creating an Entrypoint¶

To define an entrypoint for a service we use the entrypoint decorator

@service.entrypoint
def hello(name: str) -> str:
    greeting_phrase = service.get_parameter("greeting_phrase")
    logger.info(f"Greeting someone with the name: {name}")
    return f"{greeting_phrase} {name}"

This will automatically expose the hello() function to the API. We strongly recommend that you use type hints in your MVI entrypoint functions. That way, you will get type verification in your API and the auto-generated documentation will show the expected data types. Please take a look at Typing in the SDK for a more detailed guide on how typing is handled in MVI.

Note

MVI entrypoints should have JSON-compatible data as input and output. Note that numpy.ndarray and pandas.DataFrame are not JSON-compatible and must be converted to lists or dictionaries.

Notifications¶

Notifications is another feature of MVI. When a notification is raised it can be viewed on the dashboard at http://your-host or sent to an email address. To add a notification we use the notify() function. They can be placed in a conditional statement to send a notification if it’s true. With notifications added, the hello() function now looks like this

@service.entrypoint
def hello(name: str) -> str:
    greeting_phrase = service.get_parameter("greeting_phrase")
    if name == "World":
        notify(
            msg="Someone is trying to greet the World, too time consuming. Skipping!",
            severity=Severity.WARNING,
        )
        return "Greeting failed"
    logger.info(f"Greeting someone with the name: {name}")
    return f"{greeting_phrase} {name}"

Here we want to stop the user from greeting the world, because that would take a lot of time. So if the name is “World” we send a notification.

Starting the Service¶

The last thing we have to do is to ensure the service runs once it is deployed

if __name__ == '__main__':
    service.run()

Full Code¶

The code we just looked at is the same code that is generated by mvi init by default. It is fewer than 25 lines of code to create a fully functional service complete with logging, notifications and configurable parameters. All together it looks like this

import logging
from mvi import service
from mvi.communication import Severity, notify

logger = logging.getLogger(__name__)

service.add_parameter("greeting_phrase", "Hello")

@service.entrypoint
def hello(name: str) -> str:
    greeting_phrase = service.get_parameter("greeting_phrase")
    if name == "World":
        notify(
            msg="Someone is trying to greet the World, too time consuming. Skipping!",
            severity=Severity.WARNING,
        )
        return "Greeting failed"
    logger.info(f"Greeting someone with the name: {name}")
    return f"{greeting_phrase} {name}"


if __name__ == '__main__':
    service.run()

Deploying the Service¶

As a reminder from Deploying Your First Service we will deploy our new service.

>>> mvi deploy hello 1.0.0 ./my_first_mvi_project/ 
Deploying service...
Service deployed successfully
MAIN    NAME    VERSION    STATUS    RUNNING
------  ------  ---------  --------  -----------------------------------
*       hello   1.0.0      running   Running (since 2020-11-23 10:29:01)

What’s Next?¶

Now you have seen the different components of the SDK and you should be ready to create your own service. The next step could be to take a look at the manager Dashboard, or the Software Development Kit documentation.