Building Microservices with SailsJS and NodeJS

I have been developing applications with uServices for sometime. Each time I wrote a new application I could not figure out where to put the uService Definitions. They tended to be spread all over my source tree. Since I was writing my application using sailsjs I wanted to follow the convention over configurability paradigm that they espouse in sails.

Here are some of the things that I tried.

• api/workers directory - Using the sails_hook_publisher & sails_hook_subscriber
• api/jobs directory - similar to the workers pattern but using grunt to run processes.
• deploy directory - Using the micro npm module.

Workers

This method uses the sails_hook_publisher & sails_hook_subscriber plugins to give each instance the ability to subscribe to jobs that are are requested from another service. It assumes that you are using redis as the message queue. And it does not handle the management of starting/stopping or replicating services. It is a good solution but it had the overhead of a full sails application with each worker. It also tied the logical to the deployment models too tightly for me.

Jobs

Very similar to the publish/subscribe worker paradigm but I wanted a light weight mechanism for spinning up small services without all of the overhead of the sails stack. So I basically just fired up small node js scripts that I stored in the jobs directory. Problems with this is lack of flexibility of the micro-service architecture and coupling with the application code.

Deploy

Using the micro npm package to create simple micro services that can handle a HTTP request. I created simple micro services that performed specific tasks for the application. Creating the micro services was actually very simple thanks to the micro package. But Deploying multiple micro services can be hard manage. So I looked to docker and containers to help with this.

I had to come up with a strategy to define/code my microservices, how they would be managed and deployed. I had to remember the key software engineering principles of Cohesion, Decoupling and Reuse in my architecture. So the first thing I worked on was decoupling the microservice deployment from the microservice source code itself.

This gave me the flexibility to change my deployment architecture from source code itself. To do this I looked at defining my deployment architecture using docker both DockerFile and docker compose file formations. To define a microservice I had to do the following.

• create a package.json file with all of the packages needed to run my microservice
• create a Dockerfile to build the image of my microservice
• add the microservice to a docker-compose file for the application.

package.json

The package.json file contains the npm packages that my microservice depends on as well as an scripts that are needed to manage my microservice including a build and deploy script. Note that when I build my microservice image I tag it with a local registry service using "localhost:5000/appName/userviceName" where appName is the name of the application and userviceName is the name of the microservice that I am creating. This is just an example of a naming convention that I like to use. If I was creating a microservice that I was going to use over and over again I would use a different name. The deploy target pushes the image into the local registry so I can use the image in the docker swarm that I am running.

 {
  "main": "index.js",
  "scripts": {
    "start": "micro",
    "build": "docker build . -t localhost:5000/appName/userviceName",
    "deploy": "docker push localhost:5000/appName/userviceName"
  },
  "dependencies": {
    "micro": "latest",
    "node-fetch": "latest"
  }
} 

Dockerfile

The dockerfile in this case is very simple. I am writing all of my micro-services in node so I start with the base image. Next I simply copy the package.json file to an application directory and I copy any of the source code into the application directory. Then I call "npm install" this will install all of the packaging that are required by my micro-service for the image. Then the last statement launchs the microservice by calling "npm start".

FROM  node:latest
RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app
COPY package.json /usr/src/app/
RUN npm install
COPY . /usr/src/app
EXPOSE 3000
CMD npm start

docker-compose.yaml

The docker-compose.yaml file contains the services and their deployment configurations for the application. For my application I have a simple web server that is the main microservice for my application. It is a sailsjs application. I try to always name my web interface micro-service "web". It is easy for me to find them later. Again in the file below I have appName as the name of the application. Also you can see the micro-service definition is runing 5 replicas and the image is the same one as defined in the Dockerfile above.

version: '3'
services:
  mongo:
    image: mongo
    expose:
         - 27017
    ports:
         - "27017:27017"
  appName:
    image: localhost:5000/appName/web
    expose:
      - 1337
    ports:
      - "1337:1337"
  userviceName:
    image: localhost:5000/appName/userviceName
    deploy:
            mode: replicated
            replicas: 5

Bouquet Generator implementation

I have created a sails generator to generate the directory heiarchy as well as simple micro-services that you can use as a starting point for your own micro-service application check out the documernation at https://github.com/madajaju/bouquet/tree/master/sails-generate-bouquet-uservice. Or you can install it by installing the node.

# npm install sails-generate-bouquet-uservice --save.

I hope this helps you with your journey to building your own sails application using micro-services.
For more information on the Bouquet sails generators check out my previous blog post at https://darrenpulsipher.blogspot.com/2017/05/resurrecting-bouquet_3.html.

DWP