AWS CloudWatch

  • AWS CloudWatch monitors AWS resources and applications in real-time.
  • CloudWatch can be used to collect and track metrics, which are the variables to be measured for resources and applications.
  • CloudWatch alarms can be configured
    • to send notifications or
    • to automatically make changes to the resources based on defined rules
  • In addition to monitoring the built-in metrics that come with AWS, custom metrics can also be monitored
  • CloudWatch provides system-wide visibility into resource utilization, application performance, and operational health.
  • By default, CloudWatch stores the log data indefinitely , and the retention can be changed for each log group at any time
  • CloudWatch Alarm history is stored for only 14 days

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CloudWatch Architecture

  • CloudWatch collects various metrics from various resources
  • These metrics, as statistics, are available to the user through Console, CLI
  • CloudWatch allows creation of alarms with defined rules
    • to perform actions to auto scaling or stop, start, or terminate instances
    • to send notifications using SNS actions on your behalf

CloudWatch Concepts

Metrics

  • Metric is the fundamental concept in CloudWatch.
  • Uniquely defined by a name, a namespace, and one or more dimensions
  • Represents a time-ordered set of data points published to CloudWatch.
  • Each data point has a time stamp, and (optionally) a unit of measure

  • Data points can be either custom metrics or metrics from other

    services in AWS.

  • Statistics can be retrieved about those data points as an ordered set of time-series data that occur within a specified time window.
  • When the statistics are requested, the returned data stream is identified by namespace, metric name, dimension, and (optionally) the unit.
  • Metrics exist only in the region in which they are created
  • CloudWatch stores the metric data for two weeks
  • Metrics cannot be deleted, but they automatically expire in 14 days if no new data is published to them.
  • NOTE: From Nov 2016 AWS provides Extended Metrics Retention
    • One minute data points are available for 15 days.
    • Five minute data points are available for 63 days.
    • One hour data points are available for 455 days (15 months).

Namespaces

  • CloudWatch namespaces are containers for metrics.
  • Metrics in different namespaces are isolated from each other, so that metrics from different applications are not mistakenly aggregated into the same statistics.
  • AWS namespaces all follow the convention AWS/<service>,for e.g. AWS/EC2 and AWS/ELB
  • Namespace names must be fewer than 256 characters in length.
  • There is no default namespace. Each data element put into CloudWatch must specify a namespace

Dimensions

  • A dimension is a name/value pair that uniquely identifies a metric.
  • Every metric has specific characteristics that describe it, and you can think of dimensions as categories for those characteristics.
  • Dimensions helps design a structure for the statistics plan.
  • Dimensions are part of the unique identifier for a metric, whenever a unique name pair is added to one of the metrics, a new metric is created
  • Dimensions can be used to filter result sets that CloudWatch query returns
  • A metric can be assigned up to ten dimensions to a metric.

Time Stamps

  • Each metric data point must be marked with a time stamp to identify the data point on a time series
  • Time stamp can be up to two weeks in the past and up to two hours into the future.
  • If no time stamp is provided, CloudWatch creates a time stamp based on the time the data element was received.
  • All times reflect the UTC time zone when statistics are retrieved

Units

  • Units represent the statistic’s unit of measure for e.g. count, bytes, % etc

Statistics

  • Statistics are metric data aggregations over specified periods of time
  • Aggregations are made using the namespace, metric name, dimensions, and the data point unit of measure, within the specified time period

Periods

  • Period is the length of time associated with a specific statistic.
  • Each statistic represents an aggregation of the metrics data collected for a specified period of time.
  • Although periods are expressed in seconds, the minimum granularity for a period is one minute.

Aggregation

  • CloudWatch aggregates statistics according to the period length specified in calls to GetMetricStatistics .
  • Multiple data points can be published with the same or similar time stamps. CloudWatch aggregates them by period length when the statistics about those data points are requested.
  • Aggregated statistics are only available when using detailed monitoring.
  • Instances that use basic monitoring are not included in the aggregates
  • CloudWatch does not aggregate data across regions.

Alarms

  • Alarms can automatically initiate actions on behalf of the user, based on specified parameters
  • Alarm watches a single metric over a specified time period, and performs one or more actions based on the value of the metric relative to a given threshold over a number of time periods.
  • Alarms invoke actions for sustained state changes only i.e. the state must have changed and been maintained for a specified number of periods
  • Action can be a
    • SNS notification
    • Auto Scaling policies
    • EC2 action – stop or terminate EC2 instances
  • After an alarm invokes an action due to a change in state, its subsequent behavior depends on the type of action associated with the alarm.
    • For Auto Scaling policy notifications, the alarm continues to invoke the action for every period that the alarm remains in the new state.
    • For SNS notifications, no additional actions are invoked.
  • An alarm has three possible states:
    • OK —The metric is within the defined threshold
    • ALARM —The metric is outside of the defined threshold
    • INSUFFICIENT_DATA —Alarm has just started, the metric is not available, or not enough data is available for the metric to determine the alarm state
  • Alarms exist only in the region in which they are created.
  • Alarm actions must reside in the same region as the alarm
  • Alarm history is available for the last 14 days.
  • Alarm can be tested by setting it to any state using theSetAlarmStateAPI (mon-set-alarm-state command). This temporary state change lasts only until the next alarm comparison occurs.
  • Alarms can be disabled and enabled using theDisableAlarmActionsandEnableAlarmActions APIs (mon-disable-alarm-actionsandmon-enable-alarm-actionscommands).

Regions

  • CloudWatch does not aggregate data across regions. Therefore, metrics are completely separate between regions.

Custom Metrics

  • CloudWatch allows publishing custom metrics withput-metric-dataCLI command (or its Query API equivalentPutMetricData)
  • CloudWatch creates a new metric ifput-metric-datais called with a new metric name, else it associates the data with the specified existing metric
  • put-metric-datacommand can only publish one data point per call
  • CloudWatch stores data about a metric as a series of data points and each data point has an associated time stamp
  • Creating a new metric using the put-metric-data command, can take up to two minutes before statistics can be retrieved on the new metric using the get-metric-statistics command and can take up to fifteen minutes before the new metric appears in the list of metrics retrieved using the list-metrics command.
  • CloudWatch allows publishing
    • Single data point
      • Data points can be published with time stamps as granular as one-thousandth of a second, CloudWatch aggregates the data to a minimum granularity of one minute
      • CloudWatch records the average (sum of all items divided by number of items) of the values received for every 1-minute period, as well as number of samples, maximum value, and minimum value for the same time period
      • CloudWatch uses one-minute boundaries when aggregating data points
    • Aggregated set of data points called a statistics set
      • Data can also be aggregated before being published to CloudWatch
      • Aggregating data minimizes the number of calls reducing it to a single call per minute with the statistic set of data
      • Statistics include Sum, Average, Minimum, Maximum, Data Sample
  • If the application produces data that is more sporadic and have periods that have no associated data, either a the value zero (0) or no value at all can be published
  • However, it can be helpful to publish zero instead of no value
    • to monitor the health of your application for e.g. alarm can be configured to notify if no metrics published every 5 minutes
    • to track the total number of data points
    • to have statistics such as minimum and average to include data points with the value 0.

Supported Services

For Supported Services refer @CloudWatch Supported Services

Accessing CloudWatch

  • CloudWatch can be accessed using
    • AWS CloudWatch console
    • CloudWatch CLI
    • AWS CLI
    • CloudWatch API
    • AWS SDKs

CloudWatch Logs

Refer to blog postCloudWatch Logs

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