Amazon EC2 Auto Scaling helps you ensure that you have the correct number of Amazon EC2 instances available to handle the load for your application.
You create collections of EC2 instances, called Auto Scaling groups. You can specify the minimum number of instances in each Auto Scaling group, and Amazon EC2 Auto Scaling ensures that your group never goes below this size. You can specify the maximum number of instances in each Auto Scaling group, and Amazon EC2 Auto Scaling ensures that your group never goes above this size. If you specify the desired capacity, either when you create the group or at any time thereafter, Amazon EC2 Auto Scaling ensures that your group has this many instances. If you specify scaling policies, then Amazon EC2 Auto Scaling can launch or terminate instances as demand on your application increases or decreases.
Components in Auto Scaling groups:
- Groups - Your EC2 instances are organized into groups so that they can be treated as a logical unit for the purposes of scaling and management. When you create a group, you can specify its minimum, maximum, and, desired number of EC2 instances.
- Configuration templates - Your group uses a launch template or a launch configuration as a configuration template for its EC2 instances. You can specify information such as the AMI ID, instance type, key pair, security groups, and block device mapping for your instances.
- Scaling options - Amazon EC2 Auto Scaling provides several ways for you to scale your Auto Scaling groups. For example, you can configure a group to scale based on the occurrence of specified conditions (dynamic scaling) or on a schedule.
- Maintain current instance levels at all times - maintains a specified number of running instances at all times. Amazon EC2 Auto Scaling performs a periodic health check on running instances within an Auto Scaling group. When Amazon EC2 Auto Scaling finds an unhealthy instance, it terminates that instance and launches a new one.
- Scale manually - most basic way to scale your resources, where you specify only the change in the maximum, minimum, or desired capacity of your Auto Scaling group. Amazon EC2 Auto Scaling manages the process of creating or terminating instances to maintain the updated capacity.
- Scale based on a schedule - scaling actions are performed automatically as a function of time and date. This is useful when you know exactly when to increase or decrease the number of instances in your group, simply because the need arises on a predictable schedule.
- Scale based on demand - lets you define parameters that control the scaling process. This method is useful for scaling in response to changing conditions, when you don't know when those conditions will change.
- Use predictive scaling - You can also use Amazon EC2 Auto Scaling in combination with AWS Auto Scaling to scale resources across multiple services. AWS Auto Scaling can help you maintain optimal availability and performance by combining predictive scaling and dynamic scaling (proactive and reactive approaches, respectively) to scale your Amazon EC2 capacity faster.
After determining that a newly launched instance is healthy, Amazon EC2 Auto Scaling does not immediately move on to the next replacement. It provides a window for each instance to warm up after launching, which you can configure. This can be helpful when you have configuration scripts that take time to run. To protect your application's availability, ensure that the instance warm-up period covers the expected startup time for your application, from when a new instance comes into service to when it can receive traffic.
A scaling cool down helps you prevent your Auto Scaling group from launching or terminating additional instances before the effects of previous activities are visible.
When you use simple scaling, after the Auto Scaling group scales using a simple scaling policy, it waits for a cooldown period to complete before any further scaling activities due to simple scaling policies can start. An adequate cooldown period helps to prevent the initiation of an additional scaling activity based on stale metrics.
Amazon EC2 Auto Scaling supports the following types of scaling policies:
- Target tracking scaling — With target tracking scaling policies, you select a scaling metric and set a target value. Amazon EC2 Auto Scaling creates and manages the CloudWatch alarms that trigger the scaling policy and calculates the scaling adjustment based on the metric and the target value. The scaling policy adds or removes capacity as required to keep the metric at, or close to, the specified target value. In addition to keeping the metric close to the target value, a target tracking scaling policy also adjusts to changes in the metric due to a changing load pattern.
- Step scaling — Increase or decrease the current capacity of the group based on a set of scaling adjustments, known as step adjustments, that vary based on the size of the alarm breach.
- Simple scaling — Increase or decrease the current capacity of the group based on a single scaling adjustment.
- Scaling Options:
- Maintain current instance levels at all times
- Scale manually - specify only the change in the maximum, minimum, or desired capacity
- Scale based on a schedule - as a function of time and date. you know exactly when.
- Scale based on demand - scaling in response to changing conditions.
- Use predictive scaling - Amazon EC2 Auto Scaling in combination with AWS Auto Scaling to scale resources across multiple services. Scales your Amazon EC2 capacity faster.
- Before you can create an Autoscaling Group you need to create a Launch configuration.
- If add multiple subnets, it will distribute instances between subnets.
- Warm-up time is the how much time new instances need to start being considered as functional in the scaling group.
- Scaling policies