Can't get AWS cloudwatch metrics for Elasticache in Java

Question

I am trying to retrieve some Elasticache metrics from CloudWatch using Java SDK 1.x. I have several classes for multiple services, and they all work, except for Elasticache. This class is passed a list of Elasticache nodes, along with start and end times. For each node, I'm attempting to retrieve some metrics from Elasticache with a 30-minute period. However, for some reason, I keep getting values of 0.0 for each metric. I have confirmed that the metrics are not empty in the AWS console. Here's my code:

public class ElastiCacheCWMetricsRetriever {
    private final AmazonCloudWatch cloudWatchClient;

    public ElastiCacheCWMetricsRetriever(AmazonCloudWatch cloudWatchClient) {
        this.cloudWatchClient = cloudWatchClient;
    }


    public Map<String, Map<String, Object>> getElastiCacheMetrics(List<String> nodeNames, 
        String startTimeStr, String endTimeStr) {
        Map<String, Map<String, Object>> elastiCacheMetricsMap = new HashMap<>();

        try {
            SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'");
            Date startTime = dateFormat.parse(startTimeStr);
            Date endTime = dateFormat.parse(endTimeStr);

            for (String nodeName : nodeNames) {
                Map<String, Object> nodeMetrics = new HashMap<>();

                nodeMetrics.put("SwapUsage", getAverageMetricValue("AWS/ElastiCache", 
                    "SwapUsage", "CacheNodeId", nodeName, startTime, endTime));
                Double SwapUsage = getSumMetricValue("AWS/ElastiCache", "SwapUsage", 
                    "CacheNodeId", nodeName, startTime, endTime);
                System.out.println("SwapUsage for " + nodeName + " is " + 
                    String.valueOf(SwapUsage));

                nodeMetrics.put("CurrentConnections", getSumMetricValue("AWS/ElastiCache", 
                    "CurrConnections", "CacheNodeId", nodeName, startTime, endTime));

                nodeMetrics.put("DatabaseMemoryUsagePercentage", 
                getAverageMetricValue("AWS/ElastiCache", "DatabaseMemoryUsagePercentage", 
                    "CacheNodeId", nodeName, startTime, endTime) * 100.0);

                nodeMetrics.put("EngineCPUUtilization", 
                     getAverageMetricValue("AWS/ElastiCache", "EngineCPUUtilization", 
                     "CacheNodeId", nodeName, startTime, endTime) * 100.0);

                Double EngineCPUUtil = getAverageMetricValue("AWS/ElastiCache", 
                    "EngineCPUUtilization", "CacheNodeId", nodeName, startTime, endTime) * 100.0;
                System.out.println("EngineCPUUtilization for " + nodeName + " is " + String.valueOf(EngineCPUUtil));
                elastiCacheMetricsMap.put(nodeName, nodeMetrics);
            }
        } catch (Exception e) {
            System.out.println("Error in Elasticache" + e.getMessage());
        }   
        return elastiCacheMetricsMap;
    }

     private double getAverageMetricValue(String namespace, String metricName, String 
         dimensionName, String dimensionValue, Date startTime, Date endTime) {
         int period = calculatePeriod(startTime, endTime);
         return getMetricValue(namespace, metricName, dimensionName, dimensionValue, startTime, endTime, period, "Average");
     }

    private double getSumMetricValue(String namespace, String metricName, String dimensionName, String dimensionValue, Date startTime, Date endTime) {
        int period = calculatePeriod(startTime, endTime);
        return getMetricValue(namespace, metricName, dimensionName, dimensionValue, startTime, endTime, period, "Sum");
    }

    private double getMetricValue(String namespace, String metricName, String dimensionName, String dimensionValue, Date startTime, Date endTime, int period, String statistic) {
        try {
            GetMetricStatisticsRequest request = new GetMetricStatisticsRequest()
                .withNamespace(namespace)
                .withMetricName(metricName)
                .withDimensions(new Dimension().withName(dimensionName).withValue(dimensionValue))
                .withStartTime(startTime)
                .withEndTime(endTime)
                .withPeriod(period)
                .withStatistics(statistic);

            GetMetricStatisticsResult result = cloudWatchClient.getMetricStatistics(request);
            System.out.println("Result for " + dimensionValue + " is " + result.toString());
            return result.getDatapoints().isEmpty() ? 0 : result.getDatapoints().get(0).getAverage();
        } catch (Exception e) {
            System.out.println("Error in Elasticache" + e.getMessage());
            return 0;
        }
    }


    private int calculatePeriod(Date startTime, Date endTime) {
        long diffInSeconds = (endTime.getTime() - startTime.getTime()) / 1000;
        int periods = (int) Math.ceil(diffInSeconds / 1800);

        return (periods > 0) ? 1800 : 60;
    }
}

I am using System.out.println("SwapUsage for " + nodeName + " is " + String.valueOf(SwapUsage)); for troubleshooting. I am not sure where to look next. Any ideas/suggestions?

EDIT: So I tested this some more and I added this line System.out.println("Result for " + dimensionValue + " is " + result.toString()); inside getMetricValue. The result I am getting is Result for scrsquy-001 is {Label: EngineCPUUtilization,Datapoints: []}. Why is it empty and how can I get this to work?

Answer 1

Ok, so I found out what was wrong. I had a look at AWS metrics in Cloudwatch metrics(not from Elasticache Metrics tab) and it turned out that each node in Elasticache is treated as CacheClusterId, where I thought each node was CacheNodeId. So I had a cluster with 3 nodes and each node has its own CacheClusterId, and under that you have CacheNodeId like 001. In the code above I only had to change CacheNodeId to CacheClusterId and it worked like a charm.