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Lab 1 - Event Bus and Event Rules

NOTE: All lab instructions are intended to be executed from the project root folder.

This lab will deploy resources to only your primary region. Start by running the publish script for lab 1:

./publish.sh 1

You will be prompted by Terraform to apply the changes to your account:

Plan: 17 to add, 0 to change, 0 to destroy.

Do you want to perform these actions?
  Terraform will perform the actions described above.
  Only 'yes' will be accepted to approve.

  Enter a value: yes

module.sorter.aws_cloudwatch_event_bus.coin_sorter: Creating...
module.sorter.aws_sqs_queue.pennies: Creating...

After this, you should see these resources:

  • SQS 'penny', 'nickel', 'dime', and 'quarter'
  • event bus 'coin_sorter'
  • event bus rules 'penny_event_rule', etc
  • an event bus archive

lab 1 architecture

Now let's send some events to the bus! In tester.py we will generate some 'coin' objects that look like this:

{'type': 'nickel', 'year': 2013}
{'type': 'quarter', 'year': 1989}
{'type': 'dime', 'year': 1989}

...and wrap them in AWS's prescribed event structure like this:

{'Source': 'pocket-change', 'DetailType': 'nickel', 'Detail': '{"type": "nickel", "year": 2003}', 'EventBusName': 'coin_sorter'}
{'Source': 'pocket-change', 'DetailType': 'penny', 'Detail': '{"type": "penny", "year": 1917}', 'EventBusName': 'coin_sorter'}
{'Source': 'pocket-change', 'DetailType': 'penny', 'Detail': '{"type": "penny", "year": 1978}', 'EventBusName': 'coin_sorter'}

Once they are posted to the event bus, each rule will filter for its target's desired events using event patterns. The event patterns in this demo look into the 'detail' node of the event json (the actual coin payload), then compare the 'type' to a string constant to determine whether the event should pass or not. Here is the event pattern for pennies:

{
  "detail": {
    "type": [{
      "equals-ignore-case": "penny"
    }]
  }
}

Testing!

So let's try it! Execute the tester script to send some coins to the event bus:

# activate the python venv
$ source .venv/bin/activate
$ python tester.py -cc 100
{'type': 'penny', 'year': 1930}
{'type': 'nickel', 'year': 2014}
{'type': 'penny', 'year': 1943}
{'type': 'dime', 'year': 1923}
{'type': 'quarter', 'year': 1955}
{'type': 'nickel', 'year': 1900}
{'type': 'quarter', 'year': 1924}
{'type': 'nickel', 'year': 1979}
{'type': 'penny', 'year': 1976}
{'type': 'nickel', 'year': 1976}

You should now see messages available in your SQS console.
Note that your messages may not add up to 100 because the script also generates some 'dollar' coins, which we are not handling yet.

sqs example

Run a few more tests with varying amounts of coins. Adding '-p' will empty the queues before sending the events. The SQS API will only allow one purge call every 60 seconds, you may see an error regarding this, or attempts to purge queues that don't exist yet but will in later labs. Do not worry, this is to be expected.
Purging queues and sending 100 coins: python tester.py -p -cc 100

Lab 1 Complete!

New you've seen some basic usage of Event Bus. Please proceed to Lab 2 - Archiving and Event Replay.