Cloudwatch指标永不返回任何结果

Question

I've been trying to get a simple application going that returns some cloudwatch metrics. I've tried 3 different web examples and none are returning any data. I can see the data on the AWS console. Perhaps someone can spot my error or point me to a simple example that is know to work?

The principal I want to achieve is: I want to know when our application gets close to its dynamoDB read/write limits and then increase them. I assume I need to write some thread that polls asking for stats, and if it reaches say 80% of capacity, increases the limits.

private static void findCloudWatchData() throws InterruptedException {
    AmazonCloudWatchClient cloudWatch = new AmazonCloudWatchClient(new BasicAWSCredentials(key, secret));
    cloudWatch.setEndpoint("monitoring.eu-west-1.amazonaws.com");

    GetMetricStatisticsRequest getMetricStatisticsRequest = new GetMetricStatisticsRequest();

    GregorianCalendar g = new GregorianCalendar(2012, 9, 17, 12, 0);

    getMetricStatisticsRequest.setStartTime(g.getTime());
    g.add(Calendar.DAY_OF_MONTH, 2);
    getMetricStatisticsRequest.setEndTime(g.getTime());

    getMetricStatisticsRequest.setNamespace("AWS/DynamoDB");
    getMetricStatisticsRequest.setMetricName("SuccessfulRequestLatency");
    getMetricStatisticsRequest.setPeriod(5*60);

    Dimension tableDimension = new Dimension();
    tableDimension.setName("TableName");
    tableDimension.setValue("personalisation.user_favourite-int");

    Dimension operationDimension = new Dimension();
    operationDimension.setName("Operation");
    operationDimension.setValue("Query");

    getMetricStatisticsRequest.setDimensions(Arrays.asList(tableDimension, operationDimension));

    Collection<String> statistics = new ArrayList<String>();
    statistics.add("Average");

    getMetricStatisticsRequest.setStatistics(statistics);
    getMetricStatisticsRequest.setUnit(StandardUnit.Count);

    //results
    GetMetricStatisticsResult result = cloudWatch.getMetricStatistics(getMetricStatisticsRequest);
    System.err.println(result.getDatapoints().size());  //this returns 0 always
    for (Datapoint p : result.getDatapoints()) {
        System.out.println(p.getTimestamp() + " " + p.getAverage());
    }
 }

Answer 1

I found the problem. If i change "SuccessfulRequestLatency" to this:

    getMetricStatisticsRequest.setMetricName("ConsumedWriteCapacityUnits");

Or getMetricStatisticsRequest.setMetricName("ConsumedReadCapacityUnits");

and set the date like this:

    now.add(Calendar.MINUTE, -5);
    getMetricStatisticsRequest.setEndTime(now.getTime());
    now.add(Calendar.DAY_OF_MONTH, -1);
    getMetricStatisticsRequest.setStartTime(now.getTime());

It starts to return data. Embarrassingly, I've used the date range incorrectly, and assumed month=9 was Sept, when in fact month=8 is September. Dynamo does not throw any invalid range exceptions.

Answer 2

I suggested in the comments, you may rely on CloudWatch alarms for this. It will avoid you the pain of running you own monitoring tool.

You can attach ' actions ' to alarm. One of the actions is SNS topic . SNS in turn can be used to trigger HTTP(S) call, send JSON, feed SQS , ...

This may be a bit more work work to setup but I believe it will be much, much easier to maintain. Btw, you will easily fit in the free Tier.