BuildOASP4FnApplication

Table of Contents

• Build your OASP4Fn application
• Result of the tutorial: Jump the Queue
• Install tools
  • Visual Studio Code
  • Node.js
  • Typescript
  • Yarn
  • Serverless
• Starting our project through a template
• Local database set up
• AWS credentials
• Adding Typings
• Start the development

Build your OASP4Fn application

In this chapter we are going to build a serverless backend with OASP4Fn. The main objective of this tutorial is to take an initial contact with OASP4Fn and the necessary tools we gonna use in the development, so at the end of it the user will be enough confident to start developing a new project with OASP4Fn without problems.

Result of the tutorial: Jump the Queue

Install tools

In this section we’re going to introduce all the necessary tools we’re gonna need to start programming and a initial configuration if necessary.

Visual Studio Code

Download the installer from the official page and install it. Once installed, the first thing you should do is install the extensions that will help you during the development, to do that follow this steps:

1. Install Settings Sync extension.

2. Open the command palette (Ctrl+Shift+P) and introduce the command: Sync: Download Settings.

3. Provide GIST ID: d976bc200f0403d8045b7e4ee39d4361.

In the case that you are unable to set up the extensions using the method mentioned, you can also use the scripts provided in this repository.

Node.js

Go to the node.js official page and download the version you like the most, the LTS or the Current as you wish.

Typescript

Let’s install what is going to be the main language during development: TypeScript. This is a ES6 superset that will help us to get a final clean and distributable JavaScript code. This is installed globally with npm, the package manager used to install and create javascript modules in Node.js, that is installed along with Node, so for install typescript you don’t have to install npm explicitly, only run this command:

npm install –g typescript

Yarn

As npm, Yarn is a package manager, the differences are that Yarn is quite more faster and usable, so we decided to use it to manage the dependencies of OASP4Fn projects.

To install it you only have to go to the official installation page and follow the instructions.

Even though, if you feel more confortable with npm, you can remain using npm, there is no problem regarding this point.

Serverless

Lastly, we gonna install the serverless framework, that gonna help us deploying our handlers in our provider we have chosen.

npm install –g serverless

Starting our project through a template

To start with the tutorial we gonna use the oasp4fn application template, so use the following command to clone it in your local machine:

git clone https://github.com/oasp/oasp4fn-application-template.git jumpTheQueue

Before continue, remember to replace the remote repository, for one that you own:

cd jumpTheQueue\
git remote remove origin
git remote add origin <your-git-repository>

This template comes with the structure that has to have an OASP4Fn application and the skeleton of some handlers. This handlers are stored on event folders, which we can add or remove adjusting to our needs, so how we only gonna use http events, we gonna access to the cloned folder an remove the s3 folder inside the handlers and test folders:

rm handlers\S3\ -r
rm test\S3\ -r

Only remains to install the base dependencies of our code using yarn, so we only have to run:

yarn

Local database set up

The database we gonna use during this tutorial is dynamodb, the noSQL database provided by AWS, which is supported by OASP4Fn. First you have to download and start it following the amazon official documentation, once you have downloaded and started, open the dynamodb shell in this local endpoint:

http://localhost:8000/shell/

And an interactive shell will be opened in your default browser like this:

Now we gonna create a table called Queue with the opened shell, to do that write "createTable" in the text pane sited at the left side of the screen and press Ctrl + Space, this will generate a template object specifying the properties that has to be passed to the create function, so we have to modify that object, having at the end something like this:

Finally press Ctrl + Enter, and if we have specified the properties properly an output with table description will be displayed at the left side console:

AWS credentials

Although we gonna use a local instance, the aws-sdk gonna look for credentials for add to the configuration and an error will raise if the credentials are missing, so for that reason we gonna add a credentials file in an .aws folder in our home directory. Said that, first of all create the folder with the following commands:

cd %HOME% # or only 'cd' if you are in a Unix based OS 
mkdir .aws

Once you has created the folder, add a file inside called credentials and write the following:

[default]
aws_access_key_id = your_key_id
aws_secret_access_key = your_secret_key

There is not necessary to put real credentials in the file as we gonna work locally in this tutorial, you can leave it as above, without replace your_key_id or your_secret_key, so the sdk will inject the credentials and won’t throw any error, but if you already have credentials, feel free to replace them there, so you have well located for future developments.

Finally, it’s worth saying that there are more ways to pass the credentials to the sdk, but this is the best in our case, for more information about credentials take a look on to the official documentation.

Adding Typings

The template we have cloned comes with a declaration types at the root of the handlers folder with typings for AWS lambda service and events, but must add more types for the data we gonna manage, so we gonna export a interface Visitor in our declaration file, that will look like this:

Start the development

Now that we already have finish the set up of our project, we gonna add our handlers based on our design:

• One that will add the visitor to the queue

• And other to get your position in the queue

Both of the handlers will be triggered by http events with a post method, so we should delete the rest of the methods than don’t gonna use, both in the handlers and test folders. So once we have done that we gonna modify our initial handler in the template, first of all renaming it to register-handler.ts.

import oasp4fn from '@oasp/oasp4fn';
import dynamo from '@oasp/oasp4fn/dist/adapters/fn-dynamo';
import { HttpEvent, Context, Visitor } from '../../types';
import * as _ from 'lodash';

oasp4fn.setDB(dynamo);

oasp4fn.config({path: 'register'});
export async function register (event: HttpEvent, context: Context, callback: Function) {
    try {
        let visitor = <Visitor>event.body;
        let code = Math.random();
        await oasp4fn.insert('Queue', _.assign(visitor, { code: code })).promise();
        callback(null, { code: code, dateAndTime: new Date() })
    }
    catch(err){
        callback({message: 'Cannot register the visitor to the queue'})
    }
}