Update CDA.md

Author: rishabkumar7

CDA.md

@@ -1081,3 +1081,109 @@ CloudFormation.
 - Stack Update Fails:
     - The stack automatically rolls back to the previous known working state
     - Ability to see in the log what happened and error messages
+
+--------------------------------------
+
+# CloudWatch
+
+CloudWatch is used for monitoring.
+
+### Why is monitoring important?
+- To deploy applications
+    - Safely
+    - Automatically
+    - Using Infrastructure as Code
+    - Leveraging AWS components
+- Because applications are deployed, and users don’t care what services we've used
+- Users only care that the application is working!
+    - Application latency: will it increase over time?
+    - Application outages: customer experience should not be degraded
+    - Users contacting the IT department or complaining is not a good outcome
+    - Troubleshooting and remediation
+- Internal monitoring:
+    - Can we prevent issues before they happen?
+    - Performance and Cost
+    - Trends (scaling patterns)
+    - Learning and Improvement
+
+### Monitoring in AWS
+- AWS CloudWatch:
+    - Metrics: Collect and track key metrics
+    - Logs: Collect, monitor, analyze and store log files
+    - Events: Send notifications when certain events happen in your AWS • Alarms: React in real-time to metrics / events
+- AWS X-Ray:
+    - Troubleshooting application performance and errors
+    - Distributed tracing of microservices
+- AWS CloudTrail:
+    - Internal monitoring of API calls being made
+    - Audit changes to AWS Resources by your users
+
+### CloudWatch Metrics
+- CloudWatch provides metrics for every services in AWS
+- **Metric** is a variable to monitor (CPUUtilization, NetworkIn...)
+- Metrics belong to **namespaces**
+- **Dimension** is an attribute of a metric (instance id, environment, etc...).
+- Up to 10 dimensions per metric
+- Metrics have **timestamps**
+- Can create CloudWatch dashboards of metrics
+
+### CloudWatch EC2 Detailed monitoring
+- EC2 instance metrics have metrics “every 5 minutes”
+- With detailed monitoring (for a cost), you get data “every 1 minute”
+- Use detailed monitoring if you want to more prompt scale your ASG!
+- The AWS Free Tier allows us to have 10 detailed monitoring metrics
+- **Note:** EC2 Memory usage is by default not pushed (must be pushed
+from inside the instance as a custom metric)
+
+### AWS CloudWatch Custom Metrics
+- Possibility to define and send your own custom metrics to CloudWatch
+- Ability to use dimensions (attributes) to segment metrics
+    - Instance.id
+    - Environment.name
+- Metric resolution:
+    - Standard: 1 minute
+    - High Resolution: up to 1 second (StorageResolution API parameter - Higher cost)
+- Use API call **PutMetricData**
+- Use exponential back off in case of throttle errors
+
+### Alarms are used to trigger notifications for any metric
+- Alarms can go to Auto Scaling, EC2 Actions, SNS notifications
+- Various options (sampling, %, max, min, etc...)
+- Alarm States:
+    - OK
+    - INSUFFICIENT_DATA
+    - ALARM
+- Period:
+    - Length of time in seconds to evaluate the metric
+    - High resolution custom metrics: can only choose 10 sec or 30 sec
+
+### AWS CloudWatch Logs
+- Applications can send logs to CloudWatch using the SDK
+- CloudWatch can collect log from:
+    - Elastic Beanstalk: collection of logs from application
+    - ECS: collection from containers
+    - AWS Lambda: collection from function logs
+    - VPC Flow Logs:VPC specific logs
+    - API Gateway
+    - CloudTrail based on filter
+    - CloudWatch log agents: for example on EC2 machines
+    - Route53: Log DNS queries
+- CloudWatch Logs can go to:
+    - Batch exporter to S3 for archival
+    - Stream to ElasticSearch cluster for further analytics
+- CloudWatch Logs can use filter expressions
+- Logs storage architecture:
+    - Log groups: arbitrary name, usually representing an application. Log expiration policy should be defineda at this level.
+    - Log stream: instances within application / log files / containers
+- Can define log expiration policies (never expire, 30 days, etc..)
+- Using the AWS CLI we can tail CloudWatch logs
+- To send logs to CloudWatch, make sure IAM permissions are correct!
+- Security: encryption of logs using KMS at the Group Level
+
+### AWS CloudWatch Events
+- Schedule: Cron jobs
+- Event Pattern: Event rules to react to a service doing something
+    - Ex: CodePipeline state changes
+- Triggers to Lambda functions, SQS/SNS/Kinesis Messages
+- CloudWatch Event creates a small JSON document to give information
+about the change