Cross-service Communication

Microservices is a modern software architectural style where an application consists of a collection of loosely coupled and independently deployable services. These small services communicate with each other to form large and complex applications.

In this tutorial we will build a yatzee game consisting of two services, one that throws a die and another that handles the game logic.

Die Roller Service

The first service we create will generate a random number between 1 and 6 and respond with the result:

>>> mvi init
Active host: http://<your-host>
project_name [my_project]: die_roller_service

Modify the code in service.py to:

import logging
from mvi.mvi import MviService
from random import randint

mvi = MviService()

logger = logging.getLogger(__name__)


@mvi.entrypoint
def roll_die() -> int:
    return randint(1, 6)


mvi.run()

Deploy the service:

>>> mvi deploy die_roller 1.0.0 ./die_roller_service
Active host: http://<your-host>
Deploying service...
Service deployed successfully
MAIN    NAME         VERSION    STATUS    RUNNING
------  -----------  ---------  --------  -----------------------------------
*       die_roller   1.0.0      running   Running (since 2020-11-24 11:56:18)

You can test if the service works correctly by going to the interactive documentation at http://<your-host>/services/die_roller/docs.

Yatzee Service

The yatzee service will call the roll_die() method of the die_roller for each die in play. If the player gets a yatzee (all 6s) we send a notification! Let’s create the code for that service:

>>> mvi init
Active host: http://<your-host>
project_name [my_project]: yatzee_service

And modify service.py to:

import logging
from mvi.mvi import MviService, notify, Severity, call_service

mvi = MviService()

logger = logging.getLogger(__name__)


@mvi.entrypoint
def play() -> list:
    n_dice = 5
    die_rolls = []

    for _ in range(n_dice):
        die_roll = call_service(
            service_name="die_roller",
            method_name="roll_die",
        )
        die_rolls.append(die_roll)

    if sum(die_rolls) == 6 * n_dice:
        notify(
            msg="YATZEE!!!",
            severity=Severity.INFO,
            email=False,
        )

    return sorted(die_rolls)


mvi.run()

Deploy the service:

>>> mvi deploy yatzee 1.0.0 ./yatzee_service
Active host: http://<your-host>
Deploying service...
Service deployed successfully
MAIN    NAME    VERSION    STATUS    RUNNING
------  ------  ---------  --------  -----------------------------------
*       yatzee  1.0.0      running   Running (since 2020-11-24 12:15:57)

We use the call_service() function to call a method in another service. In this case, the roll_die() function of the die_roller service. Notice how we did not specify any version of die_roller, this way the main version will be used. If you wanted to specify a version, then you should use the keyword argument service_version.

Try out your new service at http://<your-host>/services/yatzee/docs.

What’s Next?

Now that you’ve come this far you have seen most of the fundamentals of MVI. Be sure that you have taken a look at the documentation for the Software Development Kit and the Command-line Interface. After which you should be ready to move on to the advanced tutorials.