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Note
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ASG (Auto Scaling Group)
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ASG automates the Scale Out and Scale In
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ASG with Load Balancer: here
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ASG with CloudWatch Alarm & Scaling: here
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ASG Dynamic Scaling Policies: here
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Target Tracking Scaling
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Simple / Step Scaling
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Scheduled Actions
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Predictive scaling
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Scale on Metrics: here
Auto Scaling Group
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In real-life, the load on your websites and application can change
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In the cloud, you can create and get rid of servers very quickly
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The goal of an Auto Scaling Group (ASG) is to:
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Scale out (add EC2 instances) to match an increased load
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Scale in (remove EC2 instances) to match a decreased load
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Ensure we have a minimum and a maximum number of EC2 instances running
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Automatically register new instances to a load balancer
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Re-create an EC2 instance in case a previous one is terminated (ex: if unhealthy)
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ASG are free (you only pay for the underlying EC2 instances)
Auto Scaling Group in AWS with Load Balancer
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ELB (Elastic Load Balancer) can run a health check
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Health check can passed on to the ASG (Auto Scaling Group)
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Terminate the instances that is unhealthy
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Can run ELB and ASG synchronously
Auto Scaling Group Attributes
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Have to create a Launch Template
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AMI + Instance Type
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EC2 User Data
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EBS Volumes
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Security Groups
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SSH Key Pair
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IAM Roles for your EC2 Instances
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Network + Subnets Information
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Load Balancer Information
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Min Size / Max Size / Initial Capacity
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Scaling Policies
Auto Scaling - CloudWatch Alarms & Scaling
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It is possible to scale an ASG based on CloudWatch alarms
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An alarm monitors a metric (such as Average CPU, or a custom metric)
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Metrics such as Average CPU are computed for the overall ASG instances
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Based on the alarm:
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We can create scale-out policies (increase the number of instances)
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We can create scale-in policies (decrease the number of instances)
Auto Scaling Groups - Dynamic Scaling Policies
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Target Tracking Scaling
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Most simple and easy to setup
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Example: I want the average ASG CPU to stay at around 40%
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Simple / Step Scaling
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When a CloudWatch alarm is triggered, then add 2 units
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When a CloudWatch alarm is triggered, then remove I
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Scheduled Actions
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Anticipate a scaling based on known usage patterns
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Example: increase the min capacity to 10 at 5pm on Fridays
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Predictive scaling
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Continuously forecast load and schedule scaling ahead
Good Metrics to Scale On
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CPUUtilization: Average CPU utilization across your instances
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RequestCountPerTarget: to make sure the number of requests per EC2 instances is stable
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Average Network In/Out (if you’re application is network bound)
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Any customer metric (that you push using CloudWatch)
Scaling Cooldowns
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After a scaling activity happens, you are in the cooldown period
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During the cooldown period, the ASG will not launch or terminate additional instances (to allow for metrics to stabilize)
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Use a ready-to-use AMI to reduce configuration time in order to be serving request faster and reduce the cooldown period
Instance Refresh
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Goal: update launch template and then re-creating all EC2 instances
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For this we can use the native feature of Instance Refresh
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Setting of minimum healthy percentage
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Specify warm-up time (how long until the instance is ready to use)d
