Integrating an application load balancer with instance groups
IBM Cloud® Application Load Balancer for VPC (ALB) is used to attach instance groups to a load balancer pool.
An instance group is a collection of virtual server instances. With them, you no longer need to manually manage your pool members. Attaching an instance group to a load balancer allows your pool back-end members to automatically scale up or down depending upon your usage and requirements.
You can choose to have a static number of instances or choose to dynamically scale instances according to your requirements. The pool members add/delete based on the application health checks and the instance group policies you configure.
For example, when application health checks fail, the system automatically adds a membership to the instance group to replace the bad member.
In addition, members can be added/deleted to the pool based on your CPU, network, and memory utilization scaling policies.
When you attach an instance group with a pool, it becomes a managed pool, and you no longer can add/delete/update members to it. However, updates to the pool are still allowed.
The maximum number of back-end members that are allowed in a load balancer pool is 50, and you cannot configure an instance group membership count beyond that limit.
Creating managed pools and instance groups
To create a managed pool, first create a regular pool and make sure that no members are attached to it. You can then attach an instance group.
To create an instance group, complete the following steps.
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Create an instance group template.
An instance group template defines your back-end member instance configurations.
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Next, create an instance group. During the instance group creation, you specify the application port, load balancer, and pool identities.
For an existing instance group, you can update it with the load balancer pool identity. You need to also choose a scaling method. You can choose from the following options:
- A static method that allows a fixed number of back-end members.
- A dynamic method for utilization-based scaling.
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Finally, create your instance group scaling policies.
Configure scaling policies only if you are using a dynamic scaling method.
When you configure these policies, you define certain metrics (like the CPU utilization percentage) and the wanted target utilization for that metric. Together, the metric and the average target utilization determine when your instance group dynamically adds or removes virtual server instances from the group.