LatencyTesterPython3

Latency tester (Python 3)

What is this function?

This function makes ping requests from the Greengrass Core and reports the round trip time of those requests.

Any time this function receives a message on any topic it will ping each host in the environment variables that start with HOST_.

NOTE: This function must run outside of the Greengrass container and must run as root so that it can create ICMP packets.

What should the environment variables look like?

The environment variables block in the function.conf should look like this:

  environmentVariables = {
    HOST_1_Default_gateway = "192.168.1.1"
    HOST_2_AWS_Virginia_console = "console.aws.amazon.com"
    HOST_3_AWS_Oregon_console = "us-west-2.console.aws.amazon.com"
    HOST_4_AWS_Singapore_console = "ap-southeast-1.console.aws.amazon.com"
  }

The format of the variable name is: HOST_X_NAME where X is a number and NAME is the name that should be included with the round trip time reports. NAME will have all underscores replaced with spaces.

The numbers for X must start at 1, must be unique, and the numbers must be sequential with no gaps (e.g. 1, 2, 4 is invalid).

The value for each variable is the host name or IP address that should be pinged. If DNS resolution may be an issue these values should only be IP addresses.

What will the output look like?

{
    "latencies": [
        {
            "name": "Default gateway",
            "unit": "Milliseconds",
            "value": 1.1777877807617188
        },
        {
            "name": "AWS Virginia console",
            "unit": "Milliseconds",
            "value": 9.070634841918945
        },
        {
            "name": "AWS Oregon console",
            "unit": "Milliseconds",
            "value": 67.3367977142334
        },
        {
            "name": "AWS Singapore console",
            "unit": "Milliseconds",
            "value": 236.07969284057617
        }
    ],
    "uuid": "d0773bbf-351e-4cf9-b198-057bdf10e53d"
}

latencies is an array of objects. Each object contains a name, unit, and value. These values were chosen because they are values that can be used easily for CloudWatch metrics and dashboards.

uuid is a unique UUID value for each message in case a downstream system needs to be able to de-duplicate the messages.