CloudWatch is probably the second most important service on AWS AFTER IAM. Why? Without CloudWatch it is almost impossible to figure out what is happening to your infrastructure running on AWS.
There are numerous main parts to CloudWatch:
Metrics - it collects data in a time series. The source of this data can be an AWS service or an application using the
Alarms - a super cool way to alert when something happens like a state changes
Dashboard - A super cool way to visualize what is happening on your metrics using the AWS management console.
Logs - the ability to extract/be sent logs from various sources
Events - simplified, event streams processing
Pricing is based on GB ingested per month, GB archived per month and alarms per month… and it MIGHT be cheaper to store logs in S3.
Metrics are time-ordered set of data points. Metrics only exist in the region they are created, can’t be deleted and expire after 14 days if no additional data is added. All metrics have a Name, a Namespace and one or dimensions. Metrics for things like non-associated EBS volumes are not reported.
Retention Policy - metrics expire after 14 days.
Log Agent - the EC2 agent; can be an RPM package or installed via a python script
Dimensions - a name/value pair that defines a category and a value for that metric. This enables sorting and grouping of metrics. Detailed monitoring enables additional dimensions.
Namespaces - containers for metrics. Each namespace is something like AWS/EBS… or to put it another way “AWS/Service”
Turning log data into metrics is done through the use of metric filters. These log file patterns get turned into metrics AFTER they have been defined developed so, no, they do not retro-actively filter data. They only return the last 50 results. They include the following key elements:
Filter pattern - what to look for
Metric Name - what should we name the metric?
Metric Namespace - what section should our new metric appear in?
Metric Value - what value do you want to publish?
Alarms take must be in same region as the data; have three states
INSUFFICIENT_DATA. Metrics are for 1 or 5 minutes so alarms have to be equal to or higher frequency. You can use the
mon-put-metric-alarm command to create or update an alarm using the ancient Java command line tool. There is a max of 5000 alarms per AWS account. Alarm history is stored for 14 days.
Using CloudWatch logs, you can monitor logs from any source in AWS, like EC2 or CloudTrail, and then archive that data. It’s an aggregation tool that will indefinitely store your logs.
Log Group - a group of log streams that have the same properties, policies, and access controls. Retention settings specify how long to keep logs from 1 day to 10 years and all streams in the group inherit this setting.
Log Stream - a series of event from the same source; auto deleted after two months
Log Event - an event that happened; includes a Timestamp and a message
Exporting, Subscriptions & Streaming
Once the data is in Cloudwatch logs, it is pretty straightforward to send it elsewhere for processsing. Subscriptions are closely related to filters… except the output of them is to a different service such as Kinesis Streams, Lambda, or Kinesis Firehose.
Logs can be exported to S3 or ElasticSearch directly from CloudWatch.
Events (CloudWatch Events)
This service is similiar to CloudTrail but faster; you might call it the central nervous system of AWS.
Events - Events take the form of small JSON documents generated when a resource changes state, an API call is delivered via CloudTrail to CloudWatch, OR when your app generates an event. Use Events instead of CloudTrail when you need real-time monitoring not batched monitoring.
Rules - code that matches and routes incoming events; all rules that match an event get fired; can process the JSON or pass the entire message
Targets - Where events are processed including Lambda, Kinesis, SNS or built-in targets
At the time this course I was taking was written, which is way far in the past, here are 5 statistics total including average, min, max, sum, and
SampleCount. To view these metrics from the command line
GetMetricStatistics API command.
Overall picture - compare SUM and difference between min and max values to get an overview of the data
Time Frames - alarms should be equal to or greater than the metric frequency