If you are using Auto Scaling Groups on AWS today then you already understand most of the basic concepts of an Elastigroup. An Elastigroup is a group of servers all with a similar configuration such as the server image, bootstrapping scripts, firewall rules, and other characteristics. If your application works across multiple servers you could have additional servers added to meet the high demand or decrease the number of servers when demand is low to save cost. Elastigroup will allow you to maintain the minimum number of servers necessary to withstand server failure or predicted spot instance replacement. The core function of Auto Scaling Groups is to maintain the necessary core number of servers running. Elastigroup function in the same way and will provision servers in your own Amazon Cloud account, within your own VPCs. The main difference is that an Elastigroup facilitates the perfect balance between Spot Instances Reserved and On-Demand Instances, achieving the most economical distribution of machines possible.
When an Elastigroup is created servers will automatically be launched to meet the minimum number of servers required. If a scaling policy is defined the “Target” number of instances will move up and down based on the scaling policy. Regardless of the “Target”, the number of servers will not be below the minimum or above the maximum number of servers that you have defined. If you are using AWS you can use Cloud Watch metrics to scale your servers (CPU Utilization > 80% for 5 minutes for example). If a server is unhealthy Elastigroup will automatically replace this server with a new one to ensure you are at the Target number of healthy servers.
Mitigating Risk of Spot Interruptions is a key feature of Elastigroup. Spotinst uses advanced algorithms combined with current Spot market data, and historical data to predict when a Spot market fluctuation will occur. If Spotinst detects that a Spot market spike or interruption is impending Elastigroup will preemptively provision a new server(s) to ensure you are at the target number of instances required. If Spot instances are too expensive Elastigroup will automatically provision On-Demand instances to ensure that you are not paying above the On Demand server price.