supermacro / pg-pubsub

Zero dependency pub-sub system

NodeJS + PG Pubsub Example

From https://gdelgado.ca/zero-dependancy-pub-sub-system-with-postgresql.html#title

Who needs RabbitMQ? ;)

This repo implements a publish / subscribe system with zero dependancies (assuming you are already using postgres as your persistence layer + Node as your runtime).

Requirements

Docker; more specifically, the docker-compose cli (link), which I believe comes as part of the default Docker install.

You don't need to have PostgreSQL or NodeJS installed.

How to run the app

1. Build images

> docker-compose up

2. Run db migrations within the node docker container

This requires you to execute an npm command from within the running node server docker container

> docker exec -it <server_container_name> bash

container_bash_session> npm run migrate

Note that the container name is most likely going to be pg-pubsub_server_1.

In the event that it is not, run docker ps to see the list of running containers on your machine. The name will appear under the right-most column called "NAMES"

3. Insert data into the db_events table

Option 1: Make HTTP requests to port 8080

Make a POST request to /users. Use postman or copy/paste the following curl command:

curl -X POST \
  http://localhost:8080/users \
  -H 'Content-Type: application/json' \
  -d '{
	"first_name": "Rick",
	"last_name": "Sanchez",
	"email": "[e-mail]",
	"cellphone": "[phone]"
}'

Ensure you have first_name, last_name, email, cellphone in your request body ... I don't have validation set up on this server.

Option 2: Make a direct insert into db_events

INSERT INTO db_events (channel, payload)
VALUES ('sms', '{ "msg": "yoloooo!" }')

Any messages with the channel set to "sms" should log a string to stdout

> Twilio: sending sms

This is because this example hooks up a subscriber inside the node runtime for all sms messages coming from PostgreSQL.

Connecting to the db

Info can be found in the Docker-compose.yml file.

POSTGRES_USER: 'gio'
POSTGRES_PASSWORD: 'testing123'
POSTGRES_DB: 'my_db'

The db is exposed on port 15432.

Structure

Implementing the "Pub" in Pub / Sub

The migrations folder contains the schemas / triggers / and SQL functions necessary to implement the publishing aspect of the system.

More specifically, there's a db_events table which stores messages sent into the pub sub system. Further, there is a trigger made that executes a sql function on any insertion into the db_events.

Implementing the "Sub" in Pub / Sub

Inside src/services/client.ts, I use the pg module to:

1. Connect to the db
2. Listen to "pub_sub" events being invoked from within postgres (which I've defined in the migrations)
3. Invoke any asynchronous functions associated with the various events that can occur in the system.