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OPTIS Poller

An AWS Lambda function that makes a request to the OPTIS Stop Monitoring request/response endpoint, filters out any non-departure records and publishes the useful data for any departures received to an AWS Simple Notification Service (SNS) topic.

AWS Permissions

The Lambda function needs an IAM role which grants the following permissions:

{
  "Action": [
    "SNS:Publish"
  ],
  "Effect": "Allow",
  "Resource": "arn:aws:sns:<region>:<account-id>:<topic-name>"
}

Where <region> is the AWS region (e.g. eu-west-1), <account-id> is the AWS account ID and <topic-name> is the name given to the SNS topic.

Environment

The following values need to be configured as environment variables:

  • AWS_SNS_TOPIC_ARN - The AWS SNS topic ARN to publish departures to
  • OPTIS_STOP_MONITORING_REQUEST_URL - The OPTIS endpoint to make requests to
  • OPTIS_TIMEOUT (optional) - The timeout in seconds for making a request and receiving a response from OPTIS. Defaults to 30.
  • OPTIS_API_KEY - The API key to access OPTIS
  • OPTIS_REQUESTOR_REF - A requestor reference with permissions to access the resource on OPTIS
  • OPTIS_PREVIEW_INTERVAL - An ISO8601 duration string specifying the period of time we want departures for; e.g. PT2H means we want the departures for the next two hours
  • OPTIS_MAXIMUM_STOP_VISITS - A numeric value specifying the maximum number of records that OPTIS should return; e.g. 200

Execution

The function requires an event payload containing the ATCO code of a bus station; e.g.

{
  "atcocode": "1800BNIN"
}

This will need to be configured with AWS CloudWatch Scheduled Events, or a similar service.

The Lambda function should be executed independently per location and ideally with a reasonable gap between requests, so that we don't flood OPTIS with multiple requests at the same time.

Output Payload

The function will publish a payload containing a JSON representation of a departures struct to the SNS topic.