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Running OPAL-server with Apache Pulsar

Introduction​

OPAL-server supports multiple backbone pub/sub solutions for connecting distributed server instances. This guide explains how to set up and use Apache Pulsar as the backbone pub/sub (broadcast channel) for OPAL-server.

Apache Pulsar as the Backbone Pub/Sub​

What is a backbone pub/sub?​

OPAL-server can scale out both in number of worker processes per server and across multiple servers. While OPAL provides a lightweight websocket pub/sub for OPAL-clients, multiple servers are linked together by a more robust messaging solution like Apache Pulsar, Kafka, Redis, or Postgres Listen/Notify.

Broadcaster Module​

Support for multiple backbone solutions is provided by the Permit's port of the Python Broadcaster package. To use it with Apache Pulsar, install the permit-broadcaster[pulsar] module:

pip install permit-broadcaster[pulsar]

Setting Up OPAL-server with Apache Pulsar​

Configuration​

To use Apache Pulsar as the backbone, set the OPAL_BROADCAST_URI environment variable:

OPAL_BROADCAST_URI=pulsar://pulsar-host-name:6650

The "pulsar://" prefix tells OPAL-server to use Apache Pulsar.

Pulsar Topic​

OPAL-server uses a single Pulsar topic named 'broadcast' for all communication. This topic is automatically created when the producer and consumer are initialized.

Docker Compose Example​

Here's an example docker-compose.yml configuration that includes Apache Pulsar:

version: '3'
services:
  pulsar:
    image: apachepulsar/pulsar:3.3.1
    command: bin/pulsar standalone
    ports:
      - 6650:6650
      - 8080:8080
    volumes:
      - pulsardata:/pulsar/data
      - pulsarconf:/pulsar/conf

  opal-server:
    image: permitio/opal-server:latest
    environment:
      - OPAL_BROADCAST_URI=pulsar://pulsar:6650
    depends_on:
      - pulsar

volumes:
  pulsardata:
  pulsarconf:

Run this configuration with:

docker-compose up --force-recreate

Allow a few seconds for Apache Pulsar and OPAL to start up before testing connectivity.

Triggering Events​

You can trigger events using the OPAL CLI:

opal-client publish-data-update --src-url https://api.country.is/23.54.6.78 -t policy_data --dst-path /users/bob/location

You should see the effect in:

  • OPAL-server logs: "Broadcasting incoming event"
  • OPAL-client: Receiving and acting on the event
  • Pulsar: Event data in the 'broadcast' topic

Supported Backends​

BackendEnvironment VariableDocker Compose Service
KafkaBROADCAST_URL=kafka://localhost:9092docker-compose up kafka
RedisBROADCAST_URL=redis://localhost:6379docker-compose up redis
PostgresBROADCAST_URL=postgres://localhost:5432/broadcasterdocker-compose up postgres
PulsarBROADCAST_URL=pulsar://localhost:6650docker-compose up pulsar

Advanced: Publishing Events Directly to Pulsar​

You can trigger events by publishing messages directly to the 'broadcast' topic in Pulsar. Ensure the message format follows the OPAL-server schema for backbone events.

Conclusion​

This guide covered setting up and using Apache Pulsar as the backbone pub/sub for OPAL-server. By following these instructions, you can effectively scale your OPAL deployment across multiple servers.

Further Resources​

For more information or support, please refer to the OPAL community forums or contact the maintainers.