AutoSpotting/AutoSpotting

// Copyright (c) 2016-2022 Cristian Măgherușan-Stanciu
// Licensed under the Open Software License version 3.0

package autospotting

import (
    "encoding/json"
    "errors"
    "log"

    "github.com/aws/aws-lambda-go/events"
)

const (
    // InstanceStateChangeNotificationMessage store detail-type of the CloudWatch Event for
    // the Amazon EC2 State Change Events
    InstanceStateChangeNotificationMessage = "EC2 Instance State-change Notification"

    // InstanceStateChangeNotificationCode store the 3 letter code used to identify
    // the Amazon EC2 State Change Events
    InstanceStateChangeNotificationCode = "ISC"

    // SpotInstanceInterruptionWarningMessage store detail-type of the CloudWatch Event for
    // Amazon EC2 Spot Instance Interruption Events
    SpotInstanceInterruptionWarningMessage = "EC2 Spot Instance Interruption Warning"

    // SpotInstanceInterruptionWarningCode store the 3 letter code used to identify
    // Amazon EC2 Spot Instance Interruption Events
    SpotInstanceInterruptionWarningCode = "SII"

    // InstanceRebalanceRecommendationMessage store detail-type of the CloudWatch Event for
    // Amazon EC2 Instance Rebalance Recommendation Events
    InstanceRebalanceRecommendationMessage = "EC2 Instance Rebalance Recommendation"

    // InstanceRebalanceRecommendationCode store the 3 letter code used to identify
    // Amazon EC2 Instance Rebalance Recommendation Events
    InstanceRebalanceRecommendationCode = "IRR"

    // AWSAPICallCloudTrailMessage store detail-type of the CloudWatch Event for
    // Events Delivered Via CloudTrail
    AWSAPICallCloudTrailMessage = "AWS API Call via CloudTrail"

    // AWSAPICallCloudTrailCode store the 3 letter code used to identify
    // Events Delivered Via CloudTrail
    AWSAPICallCloudTrailCode = "ACC"

    // ScheduledEventMessage store detail-type of the CloudWatch Event for
    // Amazon CloudWatch Events Scheduled Events
    ScheduledEventMessage = "Scheduled Event"

    // ScheduledEventCode store the 3 letter code used to identify
    // Amazon CloudWatch Events Scheduled Events
    ScheduledEventCode = "SCE"
)

// InstanceData represents JSON structure of the Detail property of CloudWatch event when a spot instance is terminated
// Reference = https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/spot-interruptions.html#spot-instance-termination-notices
type instanceData struct {
    InstanceID     *string `json:"instance-id"`
    InstanceAction *string `json:"instance-action"`
    State          *string `json:"state"`
}

// returns the InstanceID, State or an error
func parseEventData(event events.CloudWatchEvent) (string, *string, *string, error) {
    var detailData instanceData
    var eventTypeCode string
    var instanceID *string
    var instanceState *string
    var result error

    if err := json.Unmarshal(event.Detail, &detailData); err != nil {
        log.Println(err.Error())
        return "", nil, nil, err
    }
    eventType := event.DetailType

    // Amazon EC2 State Change Events
    if eventType == InstanceStateChangeNotificationMessage &&
        detailData.InstanceID != nil &&
        detailData.State != nil {
        eventTypeCode = InstanceStateChangeNotificationCode
        instanceID = detailData.InstanceID
        instanceState = detailData.State
    }

    // Amazon EC2 Spot Instance Interruption Events
    if eventType == SpotInstanceInterruptionWarningMessage &&
        detailData.InstanceAction != nil &&
        *detailData.InstanceAction != "" {
        eventTypeCode = SpotInstanceInterruptionWarningCode
        instanceID = detailData.InstanceID
    }

    // Amazon EC2 Instance Rebalance Recommendation Events
    if eventType == InstanceRebalanceRecommendationMessage &&
        detailData.InstanceID != nil &&
        *detailData.InstanceID != "" {
        eventTypeCode = InstanceRebalanceRecommendationCode
        instanceID = detailData.InstanceID
    }

    // Events Delivered Via CloudTrail
    if eventType == AWSAPICallCloudTrailMessage {
        eventTypeCode = AWSAPICallCloudTrailCode
    }

    // Amazon CloudWatch Events Scheduled Events
    if eventType == ScheduledEventMessage {
        eventTypeCode = ScheduledEventCode
    }

    // This code shouldn't be reachable
    if len(eventTypeCode) == 0 {
        log.Printf("This code shouldn't be reachable, received event: %+v \n", event)
        result = errors.New("this code shouldn't be reached")
    }

    return eventTypeCode, instanceID, instanceState, result
}