AWS CloudWatch (Events)

Overview

• AWS Resources publish information about state changes as CloudWatch Events
• Target can execute action upon event
• Rule can route event to Target
• Use cases
  • Invoke Lambda to modify DNS when EC2 instance is launched
  • Direct CloudTrail records to Kinesis
  • Run SSM command on when instance is launced
  • Log AWS API Calls
• Near real-time
• At least-one trigger

Event

• Triggered by:
  • AWS resource changes state, e.g
    • EC2 instance pending->running
    • ASG launches or terminates an instance
    • EBS created a snapshot
    • Code Deploy instance state change
    • Sign-in to AWS Management Console
    • [many other AWS Services]
  • AWS CloudTrail
    • Can be used as intermediary
    • Read/Write calls supported by CloudTrail can be relayed as Events
  • Customer code publishes event (PutEvents)
  • Scheduled (self-triggered)
    • Cron expressions
    • Rate expressions
• Uses JSON format
• Can contain custom payload (useful for Lambda)

Event Bus

• Each AWS account has default bus
• Allows sending events to receiver AWS account
  • On receiver account specify permissions
  • Create a rule 
  • Attach foreign Event Bus as a target

Rule

• matches incoming events and route to targets
• matching is unordered

Target

• Receives event as JSON
  • AWS Systems Manager (Run Command)
  • EC2 API calls
  • ECS tasks
  • Lambda
  • Kinesis Streams 
  • SNS
  • [other AWS Services]
  • Event Bus in another account

References

• http://docs.aws.amazon.com/AmazonCloudWatch/latest/events/DocumentHistory_cwe.html

AWS ELB(NLB)

Overview

• Operates at OSI Level 4 (connection level)
  • TCP: IP + Port
  • Level 3 would be just IP
• Full control over IP addresses
  • Single IP address per AZ (VPC subnet)
    • EIP possible to attach
    • No CNAME resolution
• Long-running connections (months) supported
  • Normally idles after timeout
  • Use cases: IoT, gaming, messaging
  • No idle-timeout configuration
• Zonality 
  • No cross-zone balancing
    • But fails over to another AZ if all targets unhealthy (Route 53)

Limitations

• No SSL termination
• No Backend server encryption

Types

• Internet-facing
• Internal

Target Types

• Instance Id or IP (just like ALB)

Performance

• Scales to millions of requests
• Very low latency
• Handles volatile traffic well
  • Sudden spike (e.g. "flash sales")

Client source IP

• Unlike other ELB it preserves source IP address
• Only applies to targets registered by instance ID (not IP targerts)
• Proxy Protocol still available 
• No need for X-Forwarded-For

Monitoring 

• VPC flow logs (instead of access logs)
• CloudWatch

Healthchecks

• Network level
  • Observes normal (organic) traffic to target 
• Application level (like CLB/ALB)
  • Synthetic

Pricing

• NLCU
  • 100K active connections / minute
  • 800 new connections (flows) / second
  • 2.22 Mbps (1 GB / h)
• Highest dimension used (like in ALB)

References

• https://aws.amazon.com/elasticloadbalancing/details/#comparehttps://aws.amazon.com/elasticloadbalancing/details/#compare

AWS ELB(ALB)

Overview

• Layer 7 (advanced)
  • Content based routing
• Evaluates listener rules
• Use cases
  • Single LB fronting different types of services (e.g. website, api)
  • Microservices in containers (integrated wih ECS)
• Improved performance over ELB (cheaper)
• Integrated with WAF
• IPv6 support

Types

• Internet facing
• Internal

Limitations

• No backend authentication (unlike CLB)

Listeners

• HTTP/HTTPS
  • Ports 1-65535
• HTTPS
  • Multiple certificates possible (SNI)
    • Smart selection if 
• WebSockets
  • HTTP (ws://) or HTTPS (wss://)
• HTTP/2
  • HTTPS listeners only
  • Server-Push not available
• Has Listener Rules (1+)

Listener Rule

• Contains
  • Priority
  • Action
    • Always forward request
  • Optional Host
    • Host-based routing
  • Optional Path
    • Path-based routing
• Default rule has no conditions (catch-all)

Target

• Type
  • EC2 instance
  • IP address
    • Inside/outside VPC (e.g. on-premise)
    • IP must be private
      • ClassicLink instances
      • Peered-VPC
      • On-premise instances (Direct Connection/VPN)
        • Use case: migrate-to-cloud/burst-to-cloud/fail-over-to-cloud
• State
  • draining
• Same target may be registered multiple times (different ports) e.g. microservices

Target Group

• Set of targets
• Listener rule forwards traffic to Target Group
• Has its own HealthCheck
  • If no healthy targets still routes traffic
• You don't need to take the whole instance out of rotation
• May be attached to Auto Scaling Group

Request Tracing

• LB injects a header X-Amzn-Trace-Id
• Supports chaining: Field={Root, Self}
• Visible in Access Logs ("trace_id")

Sticky Sessions

• Only LB cookie supported (AWSALB)
• Websockets are inherently sticky (long-lasting connection)

Healthchecks

• Ability to define "successful" HTTP status codes

Pricing

• Per-hour fee
• LCU
  • Dimenstions
    • 3000 Active Connections per minute
    • 25 new connections established per second
      • Certificate key size matters (shorter = cheaper)
    • 1000 rules evaluation
    • Data transferred 2.25 Mbps (=1 GB/per-hour)
  • Highest dimension used to evaluate number of LCUs consumed 

References

• https://docs.aws.amazon.com/elasticloadbalancing/latest/application/doc-history.html
• https://github.com/open-guides/og-aws#alb
• https://aws.amazon.com/blogs/devops/introducing-application-load-balancer-unlocking-and-optimizing-architectures/
• https://aws.amazon.com/blogs/aws/new-application-load-balancing-via-ip-address-to-aws-on-premises-resources/

AWS Batch

Overview

• Simplifies running batch jobs
• Provisions EC2 resources
  • Allows to specify % of spot instances
• Lower level than Hadoop
• No additional pricing
• Uses ECS container instances to execute jobs
• Scales to 100K+ jobs

Batch Computing Advantages

• You can shift computing when it is cheaper
• Avoids idling resources + higher efficiency
• Enables prioritization

Use Cases

• File uploaded to S3
  • SNS notification
    • Lambda submits a batch job

Job (what)

• Unit of work
  • Shell script
  • Linux executable
  • Container image (docker)
    • Pulled from internal/external registry
• Runs as containerized application
• Has AWS Job Id and Name
• Can reference other jobs (dependencies)
  • You can chain multiple jobs
• Parameters can get overridden

Job Definition (how)

• "Blueprint for resources"
• Name:RevisionNumber
• Hardware requirements
  • vCPU
  • Memory
• Mount points
• Environmental variables
• jobRoleARN - permission passed to the container

Job States

• SUBMITTED
  • Added to the queue
  • Upon evaluation by Job Scheduler transitions to 
    • PENDING (has dependencies)
    • RUNNABLE (no dependencies
• PENDING
  • cannot run due to dependencies
  • if dependency fails the parent jobs moves to FAILED, too
• RUNNABLE
  • no outstanding dependencies
  • can be started as soon as resources are available
• STARTING
  • scheduled on the host
  • container initialization is underway; transitions to
    • RUNNING
• RUNNING
  • Running as a container job on ECS container instance
• SUCCEEDED
  • Job completed with Exit code = 0
  • Logs available in CloudWatch Logs
• FAILED
  • All available attempts failed 
  • Retry
    • Trigger
      • Exit Code != 0 
      • EC2 instancec failure
      • AWS failure
    • Attempts
      • Default:1 , Max:10
      • AWS_BATCH_JOB_ATTEMPT environmental variable passed

Job Queue

• Place where submitted jobs reside until scheduled
• Priority value associated
• Has Compute Environments associated
  • Ordered, Max 3

Scheduler

• Attached to a Job Queue
• Decides when and where jobs are run (i.e. what resources)
• Dependency-aware
• Runs queues according to priorities
• FIFO

Compute Environment

• Same as ECS Cluster
• Set of compute resources
• Types
  • Managed
    • Specific Instance Types (multiple) or The Newest
    • Min/Max/Desired vCPUs
  • Unmanaged
    • AWS Batch creates ECS Cluster
    • Use when you need special resources (e.g. EFS, Dedicated Hosts)

Array Job

• Collection or
• Examples (embarrassingly parallel)
  • Monte Carlo simulations
  • Parametric sweeps
  • Large rendering jobs
• Submitted like a single job
  • Specify array size
  • AWS_BATCH_JOB_ARRAY_INDEX passed to container
• Parent Array Job has normal AWS Batch Id (e.g. 1)
  • Children have index appended (e.g. 1:0)
• Dependency type
  • SEQUENTIAL
    • A:1 cannot start until A:0 succeeds
  • N_TO_N
    • Allows to run multi-stage processing
    • Each job corresponds to input split

References

• https://aws.amazon.com/blogs/aws/aws-batch-run-batch-computing-jobs-on-aws/
• https://github.com/open-guides/og-aws#batch
• http://docs.aws.amazon.com/batch/latest/userguide/what-is-batch.html