Building a Module¶
Modules contain the functions that you want to publish to the NStack platform.
After this tutorial, we will have a simple Python module deployed to our NStack instance. This module will have a single function in it which counts the number of characters in some text.
Before starting, check that NStack is installed by running
nstack --version in your terminal. If you got information about the version of NStack you have, you’re good to go. If that didn’t work, check out Installation again.
We want to create a new Python module.
Create a directory called
Demo where you would like to build your module and
cd into that directory using your terminal. NStack uses the name of the directory as the default name of the module
To create a new module, run
nstack init -l python.
You should see the following output confirming that this operation was successful.
~> mkdir Demo.NumChars ~> cd Demo.NumChars ~/Demo> nstack init -l python python module 'Demo.NumChars:0.0.1-SNAPSHOT' successfully initialised at ~/Demo.NumChars
Because NStack versions your modules, it has given
Demo.NumChars a version number (
0.0.1-SNAPSHOT). Because the version number has a
SNAPSHOT appended to it, this means NStack allows you to override it every time you build. This is helpful for development, as you do not need to constantly increase the version number. When you deem your module is ready for release, you can remove
SNAPSHOT and NStack will create an immutable version of
init will have created some files.
~/Demo.NumChars> ls nstack.yaml requirements.txt service.py setup.py module.nml
This is the skeleton of an NStack module.
nstack.yaml is the configuration file for your module,
module.nml describes the functions and types defined in your module, and
service.py is where the code of your module lives (in this case, it’s a Python class).
setup.py are both standard files for configuring Python.
We’re going to be concerned with
service.py. For a more in-depth look at all these files, refer to Module Structure.
service.py, there is a
Service class. This is where we write the functions we want to use on NStack. It is pre-populated with a sample function,
numChars, that counts the number of characters in some text.
#!/usr/bin/env python3 # -*- coding: utf-8 -*- """ Demo.NumChars Module """ import nstack class Module(nstack.Module): def numChars(self, x): return len(x)
module.nml is where you tell NStack which of the functions in
service.py you want to publish as functions on NStack,
and their input and output schemas (also known as types).
module Demo.NumChars:0.0.1-SNAPSHOT fun numChars : Text -> Integer
In this instance, we are telling NStack to publish one function,
numChars, which takes
Text and returns an
The schema – or type – system is a key feature of NStack that lets you define the sort of data your function can take as input, and produce as output. This helps you ensure that your module can be reused and works as intended in production.
To build and publish our module on NStack, we use the
~/Demo.NumChars> nstack build Building NStack Container module Demo.NumChars:0.0.1-SNAPSHOT. Please wait. This may take some time. Module Demo.NumChars:0.0.1-SNAPSHOT built successfully. Use `nstack list functions` to see all available functions
When we run
build, the code is packaged up and sent to the server.
We can check that our
numChars function is live by running the suggested
nstack list functions command:
~/Demo.NumChars> nstack list functions Demo.NumChars:0.0.1-SNAPSHOT numChars : Text -> Integer
That’s it! Our
numChars function is live in the cloud, and is ready to be connected to input and output data streams, which the next tutorial will cover.