eventbridge-fan-in-terraform: Update AWS Provider to v6 with bug fixes and README improvements

[kakakakakku]

Issue #, if available:
N/A

Description of changes:

Hi😀 Thanks for the useful patterns!

To keep this pattern maintainable, I updated the AWS Provider to v6.

And I tried this pattern and found some issues, so I fixed them as well.

Changes

• Updated the AWS Provider to v6
• Replaced the deprecated is_enabled argument with state
• Pinned the EventBridge module version to ~> 4.3
• Fixed missing provider aliases on aws_cloudwatch_event_target and aws_cloudwatch_log_resource_policy
• Removed unused outputs and an unused Lambda handler stub (src/app.js)
• README updates

Note: a deprecation warning about inline_policy still remains, but it comes from the terraform-aws-modules/eventbridge module itself, so it should be fixed upstream.

Check

terraform apply completed successfully and I verified the fan-in works. Events published to eventBus1 / eventBus2 in us-east-2 arrived in the log group of the central event bus in ca-central-1.

$ aws events put-events --region us-east-2 --entries '[
  {
    "EventBusName": "eventBus1",
    "Source": "demo.test",
    "DetailType": "TestEvent",
    "Detail": "{\"message\": \"hello from eventBus1\"}"
  }
]'
{
    "FailedEntryCount": 0,
    "Entries": [
        {
            "EventId": "923a927e-fa40-b9c6-c8c9-68e00cb7848f"
        }
    ]
}

$ aws events put-events --region us-east-2 --entries '[
  {
    "EventBusName": "eventBus2",
    "Source": "demo.test",
    "DetailType": "TestEvent",
    "Detail": "{\"message\": \"hello from eventBus2\"}"
  }
]'
{
    "FailedEntryCount": 0,
    "Entries": [
        {
            "EventId": "c432b097-7c13-eb73-5689-fb7d65193572"
        }
    ]
}

$ aws logs tail /aws/events/central-bus-logs/logs --region ca-central-1 --since 10m
2026-08-09T09:16:52.000000+00:00 da1cd3c2-dd8f-38c8-b81e-88f87b17aabf {"version":"0","id":"0cf20d49-1ddd-7056-1356-d272597ce011","detail-type":"TestEvent","source":"demo.test","account":"000000000000","time":"2026-08-09T09:16:52Z","region":"us-east-2","resources":[],"detail":{"message":"hello from eventBus1"}}
2026-08-09T09:18:34.000000+00:00 d5a833f7-6120-34a5-add4-416fb6a0716f {"version":"0","id":"48d43345-ddd1-a3b9-da22-625717796373","detail-type":"TestEvent","source":"demo.test","account":"000000000000","time":"2026-08-09T09:18:34Z","region":"us-east-2","resources":[],"detail":{"message":"hello from eventBus2"}}

Thank you😀

---

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[kakakakakku]

note: It's unused code

[kakakakakku]

╷
│ Warning: Argument is deprecated
│ 
│   with aws_cloudwatch_event_rule.ebrule,
│   on main.tf line 15, in resource "aws_cloudwatch_event_rule" "ebrule":
│   15:   is_enabled = true
│ 
│ is_enabled is deprecated. Use state instead.
╵

[kakakakakku]

note: Added AWS CLI commands to create the fan-in event buses (the pattern assumes they already exist, but most readers need to create them first)