Multi-tenant data isolation in PostgreSQL

Blog post: https://dctalbot.nyc/blog/pg-tenant-isolation/

This repo demonstrates a postgres-native approach to tenant isolation in a basic multi-tenant web app. Python, Starlette, and SQLAlchemy are used here, but the technique can be implemented with comparable alternatives.

With this technique, developers can write SQL queries and have the result set automatically filtered to only include data belonging to a given tenant. The tenant is identified by a required runtime configuration parameter on the database session. The value of this parameter is typically sourced from an auth token in the initial client request.

This obviates the overhead of managing tenant-specific tables, schemas, or databases. Of course, if an extreme level of isolation is required, you may consider these options, plus the option of running distinct instances of your application.

sequenceDiagram
    participant client
    participant server
    participant postgres
    client->>+server:GET /items <br> {tenant_id#58; foo}
    server->>+postgres:set tenant_id = foo#59; select * from items#59;
    postgres->>-server: Data for tenant foo
    server->>-client: API response

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Getting Started

This project is lightweight and should not be a hassle to set up or tear down for most developers.

Requirements:

• Python 3.9 +
• Docker 24 +

Run the following make targets, or run the commands in the Makefile manually.

1. Ensure python is at least the version specified above.

python --version

2. Install Python dependencies in a virtual environment

make venv

3. Make sure Docker is running, and run the following command to start a local Postgres server. The init.sql script will run automatically, configuring the row security policies and inserting seed data. If you already have a process running on port 5432, you will need to stop that process first.

make pg

4. Start the web server

make start

At this point, you can make some web requests. I'm using curl and jq, but you can use the web client of your choice.

The options for X-tenant-id are:

• 7a245486-3fc8-47ec-b303-04fefe7a58ff
• 162be16f-f76d-431a-a213-171838ded9ae
• ebdba44d-ad48-4e73-9bd5-339e3c3fc590

Example 1: List all Items

curl --header "X-tenant-id: 7a245486-3fc8-47ec-b303-04fefe7a58ff" http://127.0.0.1:8000/items/ | jq

This results in the following query:

SET app.current_tenant_id = '7a245486-3fc8-47ec-b303-04fefe7a58ff'; SELECT * FROM items;

The row security policy on the items table filters out rows which do not belong to app.current_tenant_id. Thus, we receive only the following items in the API response:

[
  {
    "id": "997d0bee-351f-4b09-9dd3-2289da1ce0ba",
    "title": "art-fair",
    "tenant_id": "7a245486-3fc8-47ec-b303-04fefe7a58ff"
  },
  {
    "id": "bab62059-b702-442e-a053-7e4690d5510b",
    "title": "bench",
    "tenant_id": "7a245486-3fc8-47ec-b303-04fefe7a58ff"
  },
  {
    "id": "1bfa0393-0f74-4824-b234-052e49511a5c",
    "title": "concert",
    "tenant_id": "7a245486-3fc8-47ec-b303-04fefe7a58ff"
  },
  {
    "id": "1b94d748-6241-410c-95f5-015105316f27",
    "title": "drinking-fountain",
    "tenant_id": "7a245486-3fc8-47ec-b303-04fefe7a58ff"
  },
  {
    "id": "de5de5ab-abdd-499a-95a6-00f8c7b7130a",
    "title": "emergency-kit",
    "tenant_id": "7a245486-3fc8-47ec-b303-04fefe7a58ff"
  }
]

Example 2: List all Tenants

curl --header "X-tenant-id: 7a245486-3fc8-47ec-b303-04fefe7a58ff" http://127.0.0.1:8000/tenants/ | jq

This results in the following query:

SET app.current_tenant_id = '7a245486-3fc8-47ec-b303-04fefe7a58ff'; SELECT tenants.*, items.* FROM tenants LEFT OUTER JOIN items ON tenants.id = items.tenant_id;

The row security policies on the items and tenants tables filter out rows which do not belong to app.current_tenant_id. Thus, we receive only the following items in the API response:

[
  {
    "id": "7a245486-3fc8-47ec-b303-04fefe7a58ff",
    "name": "pawnee-parks-and-rec",
    "items": [
      {
        "id": "997d0bee-351f-4b09-9dd3-2289da1ce0ba",
        "title": "art-fair",
        "tenant_id": "7a245486-3fc8-47ec-b303-04fefe7a58ff"
      },
      {
        "id": "bab62059-b702-442e-a053-7e4690d5510b",
        "title": "bench",
        "tenant_id": "7a245486-3fc8-47ec-b303-04fefe7a58ff"
      },
      {
        "id": "1bfa0393-0f74-4824-b234-052e49511a5c",
        "title": "concert",
        "tenant_id": "7a245486-3fc8-47ec-b303-04fefe7a58ff"
      },
      {
        "id": "1b94d748-6241-410c-95f5-015105316f27",
        "title": "drinking-fountain",
        "tenant_id": "7a245486-3fc8-47ec-b303-04fefe7a58ff"
      },
      {
        "id": "de5de5ab-abdd-499a-95a6-00f8c7b7130a",
        "title": "emergency-kit",
        "tenant_id": "7a245486-3fc8-47ec-b303-04fefe7a58ff"
      }
    ]
  }
]

Tear down

When you're done, you can clean up the resources with the following command:

make clean