Monthly Archives: February 2021

How to add Capacity Providers in the existing ECS Cluster?

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A quick post on how to add Capacity Providers in ECS clusters.

In our last article, we walked you through the basics of Capacity Providers. In this article, let’s create them to test their functionalities. You can create Capacity Providers and add them to the running ECS cluster without touching anything in the cluster.

Creating EC2 type Capacity Providers

Steps:

  1. Make sure you are running EC2 backed ECS Cluster.
  2. Create new ASG using same launch template/configuration as existing ASG
  3. Create Capacity Provider
  4. Update cluster with newly created Capacity Provider.

For creating EC2 type Capacity Providers, you should use the new ASG. AWS does not recommend re-using the same ASG which is configured in ECS Cluster. You can use the same Launch template or Launch configuration and create a new ASG to be used by Capacity Providers. It makes it easy for Capacity Providers to keep track of EC2 instances instantiated by them.

While creating new ASG make sure –

  • Desired and minimum capacity is set to zero.
  • Maximum capacity is set to a non-zero number.
  • Enable instance scale-in protection. So that scale in action does not terminate EC2s running tasks.

Once ASG is ready, head back to the ECS cluster dashboard and click on Cluster name. On a cluster detail page, you should see a tab named Capacity Providers. Click on it and then click on Create button.

Creating Capacity Providers!

You should be presented with the Capacity Provider configuration page. Here you can specify –

  • Capacity provider name: Identifier
  • Auto Scaling group: Select newly created ASG from the dropdown.
  • Managed scaling: Enabled so that capacity providers can manage both scales in and scale-out.
  • Target capacity %: It defines how much capacity you want to be used for the task’s compute requirements. I chose 100% that means I don’t want the capacity providers to maintain any spare capacity for upcoming tasks. For example, if you specify 70%, then the capacity provider maintains 30% capacity spare so that any new upcoming tasks can directly be placed here and don’t need to wait in a PROVISIONING state for long. For optimum billing experience, 100% should be good enough.
  • Managed termination protection: Enabled. It prevents ASG from terminating any instance running at least one task on it during scale-in action. Your ASG should have instance scale-in protection enabled for it.
EC2 capacity provider settings

Click on Create button to create your capacity provider. You should be able to see the capacity provider on the cluster details page now.

Capacity provider information

Now, it’s time to add this capacity provider to the ECS cluster.

You can create multiple capacity providers with different ASGs so that you can leverage different instance types. And they all should be listed here as well. For the sake of this article, I am moving ahead with a single capacity provider.

Click on the Update cluster button on the Cluster details page. On the update page, capacity providers can be added/removed to the cluster.

Adding capacity provider to ECS cluster

Select a capacity provider from the dropdown and click on the Update button. If you have multiple capacity providers, then add them by clicking Add, another provider.

When adding more than one capacity provider, you need to specify Base and Weight values for each capacity provider.

You should see the above message confirming capacity provider addition is successful!

Creating FARGATE capacity providers

Well, you cant create them technically! FARGATE capacity providers are readily available in FARGATE clusters. You need to associate them with the cluster.

When you create an ECS cluster backed by FARGATE, you can see FARGATE and FARGE_SPOT types of capacity providers already available in the cluster.

FARGATE capacity providers

You can add them to the cluster by the same Update cluster process explained above.

Adding FARGATE capacity provider to cluster
Adding FARGATE capacity providers to existing cluster

If you have an existing FARGATE ECS Cluster, you need to use AWS CLI or API calls to update it with the FARGATE capacity providers.

You need to use the put-cluster-capacity-providers switch—more details on AWS documentation here. Since I don’t have any existing FARGATE cluster, I can not demonstrate it here.

Now, your cluster is updated with capacity providers and ready to run tasks on a complete auto-scaled ECS cluster!

Amazon ECS Capacity Providers Overview

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A quick rundown at Amazon ECS Capacity Providers

ECS Capacity Providers basics!

We have seen the Amazon ECS service in detail under a couple of previous articles. In this article, we will be discussing the Capacity Provider feature of the ECS service.

What are the Capacity Providers?

As you must be aware, Amazon ECS Clusters leverage EC2 or Fargate compute in the backend to run the container tasks. Before CPs, ECS was conceptualized as infrastructure first! That means you need to have infra ready before you can run the tasks. If you see the ECS’s functioning, you have to create ASG, run the desired count of instances in ASG, and then run the tasks in ECS.

ECS as infrastructure first!

With the concept of Application first, Capacity Providers came into existence. CPs are managers of infrastructure. Basically, they are providing and managing the compute capacity for running tasks in the cluster. So, you need not run instances before running tasks. You can run the tasks even if there is no infra provisioned in the cluster and when CPs detects tasks are awaiting compute to run, they will provision compute (EC2/Fargate). They work in both ways: scale out and scale in.

CPs responds to the service/application’s requirement and mange compute capacity automatically.

Types of Capacity Providers

There are two types of capacity providers offered –

  1. For ECS using EC2:
    • A capacity provider will be a logical entity grouping ASG of EC2 and setting for managed scaling, termination protection.
    • It is recommended to create a new ASG to use in this capacity provider. You may use the same launch config/template from the existing ECS ASG.
  2. For ECS using FARGATE:
    1. Amazon offers FARGATE and FARGATE_SPOT capacity providers.
    2. There are reserved and can not be created or deleted. You can directly associate them with your cluster.

Why should I move from Launch type to Capacity Providers?

All this capacity provider hype leaves many of us to the very question. Why? So let me jot down few reasons why you should consider moving to capacity providers than using launch types.

  1. Out of the box autoscaling for both scale-in and scale-out actions. So, you don’t have to engineer it using the CloudWatch matrix!
  2. You can start a cluster without provisioning any instances beforehand (desired capacity set to 0 in ASG)
  3. Capacity will be made available to tasks when you run them by scaling out ASG. This makes sure AWS bills are light on your pocket.
  4. Scale-out compute when your application takes the load and automatically scales in when load flattens. Peace of mind from management and bills!
  5. You can make use of FARGATE_SPOT!
  6. You can migrate existing ECS services to Capacity Providers without any downtime.

Downsides of Capacity Providers

There are few shorts in the capacity providers as well for now. They may improve in the future. A quick list as below –

  1. CAP is not supported if you are using Classic Load Balancers for services in the ECS cluster.
  2. CAP is not supported for blue/green deployment types for services.
  3. The scale in duration is set to 15 minutes, and you can not customize it.
  4. This leads to another issue: you should have EC2 idle for 15 minutes straight to get it nominated in scale-in action. Hence, scale in action is not aggressive and might not even happen in a crowded/spiking environment.
  5. It also does not for fragmentation of tasks, i.e., grouping them in underutilized instances, which is another reason scale-in will not be aggressive. You can try binpack placement strategy, though, to mitigate this.
  6. Once you update the service to use capacity providers, you can not update it to use EC2/previous launch type. You have to delete and re-create the service for that (includes downtime).
  7. When using the capacity provider strategy, a maximum of 6 capacity providers can be provided.

That’s all for starters! We will see Capacity Providers in action in upcoming articles.