我有一个每 2 小时运行一次的备份脚本。我想使用 CloudWatch 来跟踪此脚本的成功执行，并使用 CloudWatch 的警报来在脚本遇到问题时得到通知。
每次成功备份后，该脚本都会在 CloudWatch 指标上放置一个数据点：
mon-put-data --namespace Backup --metric-name $metric --unit Count --value 1
每当指标上的统计“总和”在 6 小时内小于 2 时，我就有一个警报进入 ALARM 状态。
为了测试这个设置，一天后，我停止将数据放入指标中（即，我注释掉了 mon-put-data 命令）。很好，最终警报进入 ALARM 状态，我收到了一封电子邮件通知，正如预期的那样。
问题是，一段时间后，警报又回到 OK 状态，但是没有新数据被添加到指标中！
已经记录了两个转换（OK => ALARM，然后 ALARM => OK），我在这个问题中重现了日志。请注意，虽然两者都显示“周期：21600”（即 6 小时），但第二个显示 startDate 和 queryDate 之间的 12 小时时间跨度；我看到这可能解释了这种转变，但我不明白为什么 CloudWatch 考虑使用 12 小时的时间跨度来计算 6 小时的统计数据！
我在这里想念什么？如何配置警报以实现我想要的（即，如果没有进行备份，则会收到通知）？
{
"Timestamp": "2013-03-06T15:12:01.069Z",
"HistoryItemType": "StateUpdate",
"AlarmName": "alarm-backup-svn",
"HistoryData": {
"version": "1.0",
"oldState": {
"stateValue": "OK",
"stateReason": "Threshold Crossed: 1 datapoint (3.0) was not less than the threshold (3.0).",
"stateReasonData": {
"version": "1.0",
"queryDate": "2013-03-05T21:12:44.081+0000",
"startDate": "2013-03-05T15:12:00.000+0000",
"statistic": "Sum",
"period": 21600,
"recentDatapoints": [
3
],
"threshold": 3
}
},
"newState": {
"stateValue": "ALARM",
"stateReason": "Threshold Crossed: 1 datapoint (1.0) was less than the threshold (2.0).",
"stateReasonData": {
"version": "1.0",
"queryDate": "2013-03-06T15:12:01.052+0000",
"startDate": "2013-03-06T09:12:00.000+0000",
"statistic": "Sum",
"period": 21600,
"recentDatapoints": [
1
],
"threshold": 2
}
}
},
"HistorySummary": "Alarm updated from OK to ALARM"
}
第二个，我根本无法理解：
{
"Timestamp": "2013-03-06T17:46:01.063Z",
"HistoryItemType": "StateUpdate",
"AlarmName": "alarm-backup-svn",
"HistoryData": {
"version": "1.0",
"oldState": {
"stateValue": "ALARM",
"stateReason": "Threshold Crossed: 1 datapoint (1.0) was less than the threshold (2.0).",
"stateReasonData": {
"version": "1.0",
"queryDate": "2013-03-06T15:12:01.052+0000",
"startDate": "2013-03-06T09:12:00.000+0000",
"statistic": "Sum",
"period": 21600,
"recentDatapoints": [
1
],
"threshold": 2
}
},
"newState": {
"stateValue": "OK",
"stateReason": "Threshold Crossed: 1 datapoint (3.0) was not less than the threshold (2.0).",
"stateReasonData": {
"version": "1.0",
"queryDate": "2013-03-06T17:46:01.041+0000",
"startDate": "2013-03-06T05:46:00.000+0000",
"statistic": "Sum",
"period": 21600,
"recentDatapoints": [
3
],
"threshold": 2
}
}
},
"HistorySummary": "Alarm updated from ALARM to OK"
}