Recently, we\u2019re about to launch a new app but we did not have any idea about the traffic we\u2019ll get. It could have been in hundreds or even thousands. So, we decided to go for Amazon\u2019s Auto Scaling feature. Auto Scaling is the appropriate solution for your app when you are not certain about your app\u2019s traffic or in cases where the traffic is really high or expected to go high during a certain period of time; be it for an hour, a day or a week.<\/p>\n
Before we discuss on how to setup auto scaling, we will discuss a bit about what is auto scaling and how it can help you tackle those unknown and uncertain traffic scenarios.<\/p>\n
What is auto scaling?<\/strong><\/p>\n It is a service provided by Amazon Web Services which allows you to scale up or down your infrastructure horizontally by automatically adding or removing EC2 instances based on user-defined policies, health status checks or schedule.<\/p>\n Auto-scaling allows you to scale your computed resources dynamically or predictably:<\/p>\n Following are the steps which can be followed to setup auto scaling:<\/p>\n Prerequisite for setting up an auto scaling<\/strong><\/p>\n Configuring auto scaling<\/strong>: [shell] [shell] Now based on\u00a0ig-asg<\/strong>\u00a0group and\u00a0ig-aslc,<\/strong>\u00a0launch configuration auto scaling will launch\u00a0two EC2 instances<\/strong>\u00a0in two different availability zones: ap-southeast-1a and ap-southeast-1b respectively. And both the instances will be behind the\u00a0igASelb<\/strong>\u00a0Elastic Load balancer. [shell] [shell] Now you\u2019ll save this ARN at safe place as it\u2019ll be required when you configure monitoring.2) Scaling Down Policy :<\/p>\n [shell] Above command will return the ARN, You will save this too.<\/p>\n [shell] Cool\u00a0 Down period in auto scaling policy takes care of scaling activities (instance launch or instance terminate).<\/p>\n As per mentioned command, you are using 300 seconds cool down period. [shell] [shell]mon-put-metric-alarm –alarm-name\u00a0sample-scale-dn\u00a0–alarm-description "Scale down at55%\u00a0load" –metric-name\u00a0CPUUtilization\u00a0–namespace AWS\/EC2 –statistic Average –period60\u00a0–threshold\u00a05\u00a0–comparison-operator LessThanThreshold –evaluation-periods\u00a05\u00a0–unit Percent –alarm-actions arn:aws:autoscaling:us-east-1:xxxxxxxxxxxxxx:scalingPolicy:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx:autoScalingGroupName\/ig-asg:policyName\/ig-scale-in[\/shell]<\/p>\n\n
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\nIt consists of four simple steps:<\/p>\n\n
\nas-create-launch-config\u00a0ig-aslc\u00a0–image-id\u00a0ami-b69e37e4\u00a0–instance-type\u00a0m1.small\u00a0–group\u00a0testingAS
\n[\/shell]<\/p>\n
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\nas-create-auto-scaling-group\u00a0ig-asg\u00a0–launch-configuration\u00a0ig-aslc\u00a0–availability-zones\u00a0"ap-southeast-1a","ap-southeast-1b"\u00a0–load-balancers\u00a0igASelb\u00a0–health-check-type ELB –grace-period 300 –max-size\u00a06\u00a0–min-size\u00a02\u00a0–desired-capacity\u00a02
\n[\/shell]<\/p>\n
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\nSo now you will create two auto scaling policies:ig-scaling-out\u00a0<\/strong>will increase the capacity of the\u00a0ig-asg<\/strong>\u00a0group and\u00a0ig-scaling-in\u00a0<\/strong>which decrease the capacity of\u00a0ig-asg<\/strong>\u00a0group.
\n1) Scaling Out Policy :<\/p>\n
\nas-put-scaling-policy\u00a0ig-scaling-out\u00a0–auto-scaling-group\u00a0ig-asg\u00a0–adjustment=2\u00a0–type ChangeInCapacity –cooldown\u00a0300
\n[\/shell]<\/p>\n
\n<\/strong><\/em>When you execute the above command it will returns the ARN that serves as a unique name for new policy.<\/p>\n
\narn:aws:autoscaling:us-east-1:xxxxxxxxxxxxxx:scalingPolicy:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx:autoScalingGroupName\/ig-asg:policyName\/ig-scale-out
\n[\/shell]<\/p>\n
\nas-put-scaling-policy\u00a0ig-scaling-in\u00a0–auto-scaling-group\u00a0ig-asg\u00a0–adjustment=-2\u00a0–type ChangeInCapacity –cooldown\u00a0300
\n[\/shell]<\/p>\n
\narn:aws:autoscaling:us-east-1:xxxxxxxxxxxxxx:scalingPolicy:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx:autoScalingGroupName\/ig-asg:policyName\/ig-scale-in
\n[\/shell]<\/p>\n
\nLet\u2019s say our auto scaling up policy has launched two new instances so it won’t terminate the server immediately. It will wait for 300 sec and then terminate the instances.<\/li>\n
\nBelow are the two commands which will do the same:<\/p>\n
\nmon-put-metric-alarm –alarm-name\u00a0sample-scale-up\u00a0–alarm-description "Scale Up at\u00a070%" –metric-name\u00a0CPUUtilization\u00a0–namespace AWS\/EC2 –statistic Average –period\u00a060\u00a0–threshold5\u00a0–comparison-operator GreaterThanThreshold –evaluation-periods\u00a05\u00a0–unit\u00a0Percent –alarm-actions arn:aws:autoscaling:us-east-1:xxxxxxxxxxxxxx:scalingPolicy:xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx:autoScalingGroupName\/ig-asg:policyName\/ig-scale-out.[\/shell]<\/p>\n