pgroll Demo

An example application to demonstrate the value of pgroll.

Architecture

The demo application is a 'todo list' application, built as a simple two-tier web app:

graph TD;
  A1([v1 Todo List UI])-->B1[v1 API];
  A2([v2 Todo List UI])-->B2[v2 API];
  B1-->D[(Postgres)];
  B2-->D;

Loading

v1 of the application allows adding new items to the todo list. v2 requires an assignee for each item.

pgroll allows v1 and v2 of the database schema to exist at the same time, making possible a zero downtime deployment of v2.

Prerequisites

• Docker
• pgroll

Install pgroll by following the installation instructions in the project README.

Running

Run the demos with:

make demo

or

make demo2

This will start three containers:

1. Postgres on host port 5432.
2. v1 of the demo application on host port 8080.
3. v2 of the demo application on host port 8081.

Applying migrations

The first migration is automatically applied by make demo.

• Apply the second migration (necessary for v2 to function):

pgroll start sql/02_add_assignee_column.json

Or, if you ran demo2:

pgroll start sql/02_check_assignee.json

Development

Run the API and the frontend:

make run
cd web
npm run start

This will run the API on port 8080 and a development build of the frontend on port 1234.

To start fresh, remove the API and postgres containers and volumes with:

make clean

Links

• Migrations workshop - A Xata migrations workshop that includes includes a runthrough of this demo.