runTask.js

const runParams = {
  taskDefinition: RUNNER,
  launchType: "FARGATE",
  networkConfiguration: {
    awsvpcConfiguration: {
      assignPublicIp: "ENABLED",
      subnets: [SUBNET]
    }
  },
  overrides: {
    containerOverrides: [
      {
        environment: [
          {
            name: "AWS_LAMBDA_HANDLER_EVENT",
            value: JSON.stringify(initialMessage)
          },
          {
            name: "AWS_LAMBDA_HANDLER_CONTEXT",
            value: JSON.stringify(context)
          },
          {
            name: "AWS_LAMBDA_HANDLER_NAME",
            value: handlerData.name
          },
          {
            name: "AWS_LAMBDA_HANDLER_PATH",
            value: handlerData.path
          }
        ],
        name: RUNNER
      }
    ]
  }
};

await ecs.runTask(runParams).promise();