AWS Relationships between EC2, ELB and ASG
EC2: An Amazon virtual machine used for hosting applications and services. EC2 instances could be pooled for scale or failover. EC2 instances could be predicated on some of the Amazon EC2 machine types.
Elastic Load Balancer (ELB): The essential load balancer supplied by Amazon. They’re used as a reverse proxy servers for pools of EC2 instances. ELBs determine instance health.
Auto Scaling Group (ASG): A get a handle on mechanism that manages how many EC2 instances constitute a pool. ASGs will create new EC2 instances predicated on configured pool sizes. They can also auto-scale up and auto-scale down the pool sizes predicated on load.
Availability Zones (AZ): An Amazon region is comprised of various data centers that have isolated power and communication. Those data centers are called Availability Zones. This escalates the option of the EC2 instance pool and reduces the impact of data center failure.
Standard Deployment
Auto Scaling Groups (ASG) and Availability Zones (AZ)
An ASG controls the amount and location of EC2 instances that produce up a worker pool.
The ASG creates new instances when needed predicated on a Launch Configuration. It generates new instances whenever a new ASG is first created, when an ASG must “size up” predicated on configuration changes or increased demand.
If ASG is destroyed then all associated instances will be destroyed. It individual instances when an ASG’s pool size settings are changed or when demand falls below the strain needed for the existing number of instances.
An ASG can distribute instances across a number of availability zones. This implies the ASG can configure the worker pool for basic HA.
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Elastic Load Balancer (ELB) and ASG
An ELB acts as a load balancer acts as a reverse proxy server for a couple of EC2 instances which were registered with the strain balancer. The ELB knows nothing about the sort or purpose of nodes in the worker pool. An ELB can forward to nodes in several Availability Zones (AZ)ASGs know how to register instances by having an ELB. This implies an ALB can automatically add and remove worker nodes because they are created or destroyed.
ELBs know about instances. ASGs know about instances and ELBs.
Relationships
ELB
- Distributes traffic across target EC2 instances
Application Scaling Group
- Creates Instances
- Distributes Instances across Availability Zones
- Registers instances with ELB
ELB
- Knows about Instances
- Doesn’t know about ASG
ELB Configuration with Cloud Formation
Basic ELB Cloud Formation templates define the strain balancer type, the availability zones and the configuration of the listeners. The ELB configuration doesn’t define the instances that the listener forwards to. Remember that the cloud formation template defines a Health Check utilized by the ELB to determine if a target instances is “healthy” enough to accept traffic.
ASG Behavior and ELB Linkage
ASGs create, destroy and manage a group of worker nodes / instances. They allocate created instances across a couple of subnets or Availability zones to create low cost highly available applications. It does not describe any group of Availability zones.
ASGs are configured with min, max and preferred number of instances. They manage their worker pool to generally meet those numbers. Some teams manage costs by problematically adjusting their min/max pool sizes later in the day or during times of low demand. It’s possible to take all an ASG’s nodes off line by setting the pool sizes to “0 “.
Dynamic autoscaling isn’t a necessary “must use” feature of an ASG.
This really is separate from autoscaling behavior where in fact the pool sizes are adjusted predicated on CPU utilization or some other metrics. Monitors can take note for resource consumption events and adjust the ASG group size accordingly.
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