PR preview environments with Neon, GitHub Actions, and AWS Lambda

Posted on 11 mins to read

You might have heard about preview environments (AKA dynamic, or ephemeral environments) in the scope of software engineering and, particularly, this term is used when speaking about the SDLC.

A preview environment — as opposed to a permanent one, like "Production", or "TST", or whatever you call them — is a short-lived environment, usually bound to a pull request. It is created on-demand when the PR is created; and destroyed when the PR is closed. It hosts a copy of the application and is used to test the changes introduced by the pull request.

If you need more information, I encourage you to jump around a few articles on the Web to grasp the idea before continuing. I won’t go into details here, but instead, I’ll be focusing on the most challenging aspect of preview environments…

The database.

Contents

The tragedy of databases in preview environments

Materials about preview environments tend to cast little light on the database, leaving you with the approximate directions, like "create a copy of the database", or "use a database per PR", but no advice on how to achieve that. And for a reason!

First of all, everyone’s application is indeed different, and there’s no one-size-fits-all solution.

But the main reason, IMO, is that a database is very different from an application and it’s hard to copy it. Databases are persistent and stateful, while applications are ephemeral and stateless. Copying apps is the same as redeploying or scaling them, maybe with a different configuration. Copying databases is always a trick.

What’s even worse, is that databases historically combine both storage and compute in them! I mean, a typical database consists of its data, represented as actual files, and a database engine, which is an application process on its own. Thus, copying a database is at least twice as hard as copying an application. Simple math!

The options here range from cloning the database using dump / restore to using no copies at all, i.e. a shared DB for all the preview environments. Let’s roughly compare them.

Dump / restore Migration scripts Shared DB

Complexity

High

Medium

No

Isolation

High

High

No

Data freshness

Medium

No

High

Automation

Low

Medium

No

Here, complexity means the amount of effort required to implement the solution. Obviously, a shared environment requires no effort; migration scripts require creating a fresh database and running the migrations; and dump / restore requires creating a fresh database, creating a dump, transferring it to the fresh database, and restoring it. Don’t get me wrong, it’s not impossible, it’s just disproportionately hard and slow.

Data isolation is high for both dump / restore and migration scripts approaches because each preview environment has its own database. A shared database, on the other hand, is not isolated at all.

Data isolation is highly correlated with the ability to test and preview schema modifications. Actually, it’s the same thing, I just want to highlight it, because it’s important. If you have a shared database, you can’t easily modify the schema without breaking others. However, if you have a dedicated database, you can do whatever you want with it. The ability to test and preview schema modifications is a huge advantage of preview environments because it allows you to test the migrations before applying them to the production database.

Isolation is the opposite of data freshness. I call it the ability for the preview environment to have the latest data from the upstream database. A shared database has the freshest data because it’s the same database. Dump / restore approach could provide fresh data as well, especially if you dump and restore the database on every PR. Migration scripts are the worst here because they don’t provide any data fresh data at all. Only the data captured in the migration / seed scripts would be available.

Migration scripts approach is somewhat automated. In the best-case scenario, you would have a script that creates a fresh database (e.g. a Terraform or Helm), and a script that runs the migrations (e.g. Rails Migrations or Liquibase). Dumping and restoring is less automated because most probably, it would involve a bash scripting with, let’s say, pg_dump and pg_restore commands. No copy approach requires no automation at all.

Compromises, compromises, compromises… As you see, you trade complexity for convenience. And because of that and because deep data isolation is rarely required, and because schema modification could be arranged manually, I suppose most projects start from a shared DB approach and never move further.

Meet Neon

Now, after such a long introduction, this section would be ridiculously (in a good way) short, even in my wordy style.

Imagine there is a PostgreSQL database, that is:

  • Fully managed

  • Serverless

  • Autoscalable

  • Auto-suspendable

  • Separates storage and compute

  • Branches in a second with a single button click or API call

  • And, yes, provides REST API for everything

  • Provides generous free tier to get you started

  • Well-documented

It exists, and it is Neon.

Because of the unique architecture, with separated storage and compute, Neon enables instant copy-on-write branching. You could create a branch, i.e. a copy of the database, from virtually any point in time in the upstream database, and it would be created in seconds. It means, that you could branch off the production database, with the latest data, and still have full isolation. Being serverless also means that Neon is very elastic, it can scale up and down, and even suspend the compute completely when it’s not used. On top of that, Neon provides a REST API for everything, so you can automate the whole process.

It’s simple to use, it’s highly isolated, it provides branches off the latest data, and it’s easily automatable. It’s perfect for preview environments.

Dump / restore Migration scripts Shared DB Neon

Complexity

High

Medium

No

Low

Isolation

High

High

No

High

Data freshness

Medium

No

High

High

Automation

Low

Medium

No

High

Drawbacks? Well, it’s in the technical preview stage yet.

I don’t see a point in repeating the docs here, so here are some rabbit holes for you:

Exploring Neon branching with GitHub Actions and AWS Lambda

Link for the impatient ones: madhead/neonbranch.

Imagine an overengineered rock-paper-scissors game, storing game rules in a database and providing a REST API to calculate the winner. The API is of no interest today, so it’s just an AWS Lambda, implemented in Python and deployed with CDK. Meet the database:

player1 player2 winner

rock

rock

NULL

rock

paper

paper

rock

scissors

rock

paper

rock

paper

paper

paper

NULL

paper

scissors

scissors

scissors

rock

rock

scissors

paper

scissors

scissors

scissors

NULL

Now, imagine we’re working on two new features. The first one expands the game with Spock and lizard, and the second one adds textual descriptions for the outcomes:

What would the database look like

player1 player1 winner description

rock

rock

NULL

It’s a tie

rock

paper

paper

Paper covers rock

rock

scissors

rock

Rock crushes scissors

paper

rock

paper

Paper covers rock

paper

paper

NULL

It’s a tie

paper

scissors

scissors

Scissors cuts paper

scissors

rock

rock

Rock crushes scissors

scissors

paper

scissors

Scissors cuts paper

scissors

scissors

NULL

It’s a tie

rock

spock

spock

☝️ Feature: descriptions

rock

lizard

rock

👈 Feature: Spock and lizard

paper

spock

paper

paper

lizard

lizard

scissors

spock

spock

scissors

lizard

lizard

spock

rock

spock

spock

paper

paper

spock

scissors

spock

spock

spock

NULL

spock

lizard

lizard

lizard

rock

rock

lizard

paper

lizard

lizard

scissors

scissors

lizard

spock

lizard

lizard

lizard

NULL

We have these changes captured in Liquibase changelogs. The question is: how do we organize the CI pipelines?

Events that trigger workflows

Remember, preview environments are ephemeral and bound to the PRs. So, let’s search for the appropriate triggers in Events that trigger workflows.

Three things could happen to a PR in regard to our scenario:

  1. It could be opened or reopened

  2. It could be synchronized

  3. It could be closed

When a PR is opened or reopened, we should create a new Neon branch, when a PR is closed we should delete the associated branch. When a PR is synchronized, we run the same workflow as when a PR is opened or reopened, as it would be made idempotent.

Workflows

So, we’ll need three workflows:

.github/workflows/pr-env-create.yml 

name: Create PR environment

on:
  pull_request:
    types:
      - opened
      - reopened

jobs:
  pr-env-create:
    steps:
      - id: deploy
        uses: ./.github/actions/deploy
        name: Deploy
        with:
          environment: pr-${{ github.event.number }}
          neon_project: ${{ vars.NEON_PROJECT }}
          neon_token: ${{ secrets.NEON_TOKEN }}

.github/workflows/pr-env-sync.yml 

name: Synchronize PR environment

on:
  pull_request:
    types:
      - synchronize

# same as above

.github/workflows/pr-env-destroy.yml 

name: Destroy PR environment

on:
  pull_request:
    types:
      - closed

jobs:
  pr-env-create:
    steps:
      - uses: ./.github/actions/destroy
        name: Destroy
        with:
          environment: pr-${{ github.event.number }}
          neon_project: ${{ vars.NEON_PROJECT }}
          neon_token: ${{ secrets.NEON_TOKEN }}

I extracted the common logic into two actions, deploy and destroy:

Deploy action

.github/actions/deploy/action.yml 

name: Deploy
description: Deploy the lambda

inputs:
  environment:
  neon_project:
  neon_token:

outputs:
  URL:
  db_host:
  db_user:
  db_password:

runs:
  using: composite
  steps:
    - uses: actions/setup-python@v4
      with:
        python-version: 3.9

    - run: python -m venv .venv
      working-directory: deploy
      shell: bash

    - run: |
        source .venv/bin/activate
        python -m pip install -r requirements.txt
      working-directory: deploy
      shell: bash

    - id: branch
      run: |
        source .venv/bin/activate
        python branch.py
      working-directory: deploy
      shell: bash
      env:
        NEON_TOKEN: ${{ inputs.neon_token }}
        NEON_PROJECT: ${{ inputs.neon_project }}
        NEON_BRANCH: ${{ inputs.environment }}

    - uses: actions/setup-java@v3
      with:
        distribution: "temurin"
        java-version: 17
    - run: ./gradlew update
      working-directory: migrations
      shell: bash
      env:
        NEON_HOST: ${{ steps.branch.outputs.db_host }}
        NEON_DATABASE: ${{ inputs.neon_database }}
        NEON_USER: ${{ steps.branch.outputs.db_user }}
        NEON_PASSWORD: ${{ steps.branch.outputs.db_password }}

The logic is pretty simple:

  1. We install Python

  2. We set up a virtual environment and install the dependencies

  3. We run a branch.py script which we’ll see in a moment

  4. We install Java to run Liquibase

  5. We run Liquibase

Destroy action

.github/actions/destroy/action.yml 

name: Destroy
description: Destroy the preview environment

inputs:
  environment:
  neon_project:
  neon_token:

runs:
  using: composite
  steps:
    - uses: actions/setup-python@v4
      with:
        python-version: 3.9

    - run: python -m venv .venv
      working-directory: deploy
      shell: bash

    - run: |
        source .venv/bin/activate
        python -m pip install -r requirements.txt
      working-directory: deploy
      shell: bash

    - run: |
        source .venv/bin/activate
        python unbranch.py
      working-directory: deploy
      shell: bash
      env:
        NEON_TOKEN: ${{ inputs.neon_token }}
        NEON_PROJECT: ${{ inputs.neon_project }}
        NEON_BRANCH: ${{ inputs.environment }}

We just run a different script, unbranch.py.

Automation scripts

Let’s extract Neon API calls into a separate Python module:

neon.py 

import os
import time

import requests

base_url = 'https://console.neon.tech/api/v2'
headers = {
    'Accept': 'application/json',
    'Authorization': f"Bearer {os.environ['NEON_TOKEN']}"
}


def find_project(project_name: str) -> dict:
    projects = requests.get(
        url=f"{base_url}/projects",
        headers=headers,
    ).json()['projects']

    return next(project for project in projects if project['name'] == project_name)


def delete_branch(project: dict, name: str) -> dict:
    branches = requests.get(
        url=f"{base_url}/projects/{project['id']}/branches",
        headers=headers,
    ).json()['branches']
    branch = next((branch for branch in branches if branch['name'] == name))
    requests.delete(
        url=f"{base_url}/projects/{project['id']}/branches/{branch['id']}",
        headers=headers,
    )


def find_branches(project: dict, name: str) -> (dict, dict):
    branches = requests.get(
        url=f"{base_url}/projects/{project['id']}/branches",
        headers=headers,
    ).json()['branches']

    primary_branch = next(branch for branch in branches if branch['primary'])
    if name:
        branch = next((branch for branch in branches if branch['name'] == name), None)
    else:
        branch = primary_branch

    return primary_branch, branch


def get_operation_details(project: dict, operation_id: str) -> dict:
    return requests.get(
        url=f"{base_url}/projects/{project['id']}/operations/{operation_id}",
        headers=headers,
    ).json()['operation']


def create_branch(project: dict, parent: dict, name: str) -> dict:
    result = requests.post(
        url=f"{base_url}/projects/{project['id']}/branches",
        headers=headers,
        json={
            'endpoints': [
                {
                    'type': 'read_write'
                }
            ],
            'branch': {
                'parent_id': parent['id'],
                'name': name,
            }
        },
    ).json()
    operations = result['operations']

    for operation in operations:
        while True:
            operation_details = get_operation_details(project, operation['id'])
            if operation_details['status'] == 'finished':
                break
            else:
                time.sleep(5)

    return result['branch']


def find_endpoint(project: dict, branch: dict) -> dict:
    endpoints = requests.get(
        url=f"{base_url}/projects/{project['id']}/endpoints",
        headers=headers,
    ).json()['endpoints']

    return next(endpoint for endpoint in endpoints if endpoint['branch_id'] == branch['id'])


def find_role(project: dict, branch: dict) -> dict:
    roles = requests.get(
        url=f"{base_url}/projects/{project['id']}/branches/{branch['id']}/roles",
        headers=headers,
    ).json()['roles']

    return next(role for role in roles if not role['protected'])


def get_password(project: dict, branch: dict, role: dict) -> str:
    return requests.get(
        url=f"{base_url}/projects/{project['id']}/branches/{branch['id']}/roles/{role['name']}/reveal_password",
        headers=headers,
    ).json()['password']

As you see, just a bunch of functions to call Neon API. Let’s see how we use them in our scripts.

branch.py 

import os

import github
import neon

if __name__ == '__main__':
    project = neon.find_project(os.environ['NEON_PROJECT'])
    primary_branch, branch = neon.find_branches(project, os.environ.get('NEON_BRANCH'))

    if not branch:
        branch = neon.create_branch(project, primary_branch, os.environ.get('NEON_BRANCH'))

    endpoint = neon.find_endpoint(project, branch)
    role = neon.find_role(project, branch)
    password = neon.get_password(project, branch, role)

    github.mask(endpoint['host'])
    github.mask(role['name'])
    github.mask(password)

    github.set_output('db_host', endpoint['host'])
    github.set_output('db_user', role['name'])
    github.set_output('db_password', password)

unbranch.py 

import os

import neon

if __name__ == '__main__':
    neon.delete_branch(
        neon.find_project(os.environ['NEON_PROJECT']),
        os.environ['NEON_BRANCH'],
    )

While unbranch.py is pretty straightforward, branch.py is a bit more complicated. First, we find the project by its name. Then we find the primary branch we fork off and the branch for the preview environment. If the branch doesn’t exist, we create it. The creation of a branch is an asynchronous operation, so we have to wait for it to finish. Then we find the endpoint and the role for the new branch and get the password for the role. Finally, we mask the sensitive data and set the output variables for GitHub Actions. They are used later by other scripts, not shown here.

And that’s it! We now have a fully automated workflow that creates a new database branch for each environment and deletes it when the environment is deleted.

Explore the demo repository, madhead/neonbranch to learn more tricks, like this:

Two more things before you go.

First, there is an official Neon GitHub Action, but with a slightly different logic and use case: neondatabase/create-branch-action.

Second, if you’re using Vercel, there is an article for that: A database for every preview environment using Neon, GitHub Actions, and Vercel.