Tracking

Rez can emit messages to an AMQP-compatible listener such as RabbitMQ whenever a context is resolved.

Table of contents

1. Goal
2. Start RabbitMQ
3. Configure RabbitMQ
4. Configure Rez
5. Profit

Goal

Estimated time: 10 mins

We're going to create a Python script that listens for whenever a context is resolved.

Process A - Consumer	Process B - Producer
$ rez env python-3 pika -- python consumer.py [*] Waiting for messages. To exit press CTRL+C [x] Context was created by manima @ toy Packages: - pika - platform - arch - rez - python-3 [x] Context was created by manima @ toy Packages: - platform - arch - python [x] Context was created by manima @ toy Packages: - platform - arch - python - shiboken2 - PySide2	$ rez env python -- exit $ rez env PySide2 -- exit

The initial output from the consumer is from creating the context within which we run the consumer. The second one is coming from the right-hand side resolving for rez env python.

Let's go.

Test

Before we begin, let's have a closer look at what kind of data is emitted.

$env:REZ_CONTEXT_TRACKING_HOST="stdout"  # PowerShell
export REZ_CONTEXT_TRACKING_HOST=stdout  # Bash
set REZ_CONTEXT_TRACKING_HOST=stdout     # cmd

$ rez env
# Output printed here

Start RabbitMQ

Spin up a RabbitMQ instance using any means necessary. For this guide, we'll be using Docker.

$ docker run -ti --rm --name rabbit -p 5672:5672 -p 15672:15672 --hostname rabbit rabbitmq:3.7-management

Configure RabbitMQ

Now go to http://localhost:5672 and add a queue.

• Durable

Then add a exchange.

• Non-durable
• Fanout

And then bind to it.

• Routing key: REZ.CONTEXT

Now RabbitMQ is setup to listen for messages, it's time to get Rez to send some.

Configure Rez

Rez doesn't emit any message until you tell about where to find your RabbitMQ instance.

rezconfig

context_tracking_host = 'localhost:5672'
context_tracking_amqp = {
    "userid": "guest",
    "password": "guest",
    "exchange_name": "myexchange",
}

Now try sending a few messages.

$ rez env -- exit
$ rez env -- exit
$ rez env -- exit

You should see 3 new messages in myqueue.

Profit

Now when you resolve an environment, a message is emitted to RabbitMQ. What we've got at the moment is akin to..

1. Having written a letter (You, the producer)
2. Delivering it to the post-office (RabbitMQ, the exchange)
3. ...

What's missing is the post-office actually delivering it, and for that we need a consumer.

Prerequisites

You can use any suitable client to RabbitMQ, in this guide we'll use pika.

consumer.py

import pika
import json


def on_resolve(ch, method, properties, body):
    payload = json.loads(body)

    try:
        context = payload["context"]
    except KeyError as e:
        print(" [x] Received %s" % body)
    else:
        print(" [x] Context was {action} by {user} @ {host}".format(**payload))
        print("     Packages:")
        for pkg in context["resolved_packages"]:
            print("     - %s" % pkg["variables"]["name"])


param = pika.ConnectionParameters(host='localhost')
connection = pika.BlockingConnection(param)

channel = connection.channel()
channel.basic_consume(queue='myqueue',
                      on_message_callback=on_resolve,
                      auto_ack=True)

print(' [*] Waiting for messages. To exit press CTRL+C')
channel.start_consuming()

Now run it, like so.

$ rez env pika python -- python consumer.py
 [*] Waiting for messages. To exit press CTRL+C
 [x] Context was created by manima @ toy
     Packages:
     - pika
     - platform
     - arch
     - rez
     - python
     - localz