How to use infrastructure as code to manage Kubernetes clusters

As more and more organizations transition to containerized applications, Kubernetes has emerged as the go-to orchestration tool for managing container workloads. Kubernetes allows developers to deploy, scale, and manage containerized applications in a reliable and scalable way. However, managing Kubernetes can be a daunting task, especially when it comes to managing the underlying infrastructure.

Enter infrastructure as code (IaC). IaC is the practice of managing infrastructure by writing code instead of manually configuring each piece of infrastructure. By using IaC, you can automate the creation and management of your infrastructure and ensure that it remains reproducible, scalable, and consistent.

In this article, we'll explore how to use IaC tools like Terraform, Pulumi, and Amazon CDK to manage your Kubernetes infrastructure.

Why use IaC to manage Kubernetes?

Managing Kubernetes infrastructure can be a complex and time-consuming task. There are many moving parts to manage, including the nodes, the master components, and the etcd storage layer. Additionally, Kubernetes is highly configurable, with hundreds of configuration options that all need to be set correctly to ensure the cluster is running smoothly.

By using IaC to manage your Kubernetes infrastructure, you can:

• Automate the creation and management of your infrastructure
• Ensure that your infrastructure is reproducible and consistent
• Easily scale your infrastructure up or down based on demand
• Reduce the risk of human error that can come with manual configurations

Getting started with Kubernetes and IaC

Before we dive into the specifics of using Terraform, Pulumi, or Amazon CDK to manage Kubernetes, let's first make sure we have a basic understanding of Kubernetes and the different components that make up a Kubernetes cluster.

At a high level, a Kubernetes cluster consists of two types of components: the master components and the worker nodes. The master components are responsible for managing the state of the cluster, while the worker nodes are responsible for running the containerized applications.

Understanding the master components

There are several key master components that make up a Kubernetes cluster:

• kube-apiserver: The API server is the central control plane for the entire Kubernetes cluster. It exposes the Kubernetes API, which is used to interact with the cluster.
• kube-scheduler: The scheduler is responsible for creating and managing the scheduling of Pods onto Nodes in the cluster.
• kube-controller-manager: The controller manager is responsible for managing the state of the cluster through a set of controllers. These controllers ensure that the desired state of the cluster matches the actual state.
• etcd: The etcd cluster is a key-value store that is used to store the configuration data for the Kubernetes cluster.

Understanding the worker nodes

The worker nodes are where your containerized applications are run. Each worker node typically runs a container runtime (such as Docker) and a kubelet process, which communicates with the master components to receive workloads to run.

Additionally, each worker node may be configured with other Kubernetes components, such as a kube-proxy process (responsible for networking), and addons such as the Kubernetes Dashboard.

Using Terraform to manage Kubernetes

Terraform is an IaC tool that provides a declarative language for defining infrastructure as code. Terraform has a large and active community that provides support for a wide range of infrastructure resources, including Kubernetes.

To manage Kubernetes infrastructure using Terraform, you will need to use the Terraform Kubernetes provider. The provider allows you to define Kubernetes resources in your Terraform code and manages the creation and configuration of those resources in your Kubernetes cluster.

Installing the Kubernetes provider

To get started with the Kubernetes provider, you will need to install it using the Terraform provider CLI. To install the provider, run the following commands:

terraform init
terraform provider install terraform-provider-kubernetes

Creating a Kubernetes cluster with Terraform

To create a Kubernetes cluster with Terraform, you will first need to define the infrastructure resources you need using the Terraform Kubernetes provider. This will typically include:

• A Kubernetes provider block to specify the version of the provider to use
• A Kubernetes cluster resource to define the cluster itself
• A set of node resources to define the worker nodes in your cluster
• Any additional Kubernetes resources you need to configure, such as a kube-proxy or Kubernetes Dashboard addon

Here is an example Terraform configuration that creates a Kubernetes cluster:

provider "kubernetes" {
  version = "~> 1.0"
  config_context_cluster = "my-kubernetes"
}

resource "kubernetes_cluster" "mycluster" {
  name     = "my-cluster"
  location = "us-central1"

  node_pool {
    name       = "my-pool"
    machine_type = "n1-standard-1"
    disk_size_gb = 100
    disk_type    = "pd-ssd"
    auto_repair  = true
    auto_upgrade = true
    min_count    = 1
    max_count    = 3
    tags        = ["my-node-pool"]
  }
}

resource "kubernetes_service" "nginx" {
  metadata {
    name = "nginx"
  }

  spec {
    selector = {
      app = "nginx"
    }

    port {
      port = 80
      target_port = 80
    }

    type = "LoadBalancer"
  }
}

In this configuration, we define a kubernetes_cluster resource with a single node pool of three worker nodes. We also define a kubernetes_service resource to expose a "nginx" service on port 80.

Managing Kubernetes resources with Terraform

Once you have created your Kubernetes cluster using Terraform, you can then define additional Kubernetes resources using the provider. This might include things like:

• Deployments and ReplicaSets to manage the scaling and rollout of your containerized applications
• Services and Ingresses to manage network traffic to your applications
• ConfigMaps and Secrets to manage application configuration and secrets

Here is an example Terraform configuration that deploys a simple nginx application to our Kubernetes cluster:

resource "kubernetes_deployment" "nginx" {
  metadata {
    name = "nginx"
  }

  spec {
    selector {
      match_labels = {
        app = "nginx"
      }
    }

    replicas = 3

    template {
      metadata {
        labels = {
          app = "nginx"
        }
      }

      spec {
        container {
          name  = "nginx"
          image = "nginx:latest"

          port {
            container_port = 80
          }
        }
      }
    }
  }
}

In this configuration, we define a kubernetes_deployment resource to deploy an nginx application with three replicas to our Kubernetes cluster.

Managing dependencies with Terraform

As your infrastructure and application grow, you may find that you have dependencies between different pieces of infrastructure. For example, you may have a Kubernetes deployment that depends on a specific version of a database or storage backend.

Terraform provides several mechanisms for managing these dependencies. You can use depends_on to explicitly specify dependencies between resources, or you can use resource interpolation to access attributes from one resource in another.

Using Pulumi to manage Kubernetes

Pulumi is an IaC tool that allows you to write infrastructure code in the programming language of your choice (including Python, JavaScript/TypeScript, and Go). This allows you to use the full power of a modern programming language to manage your infrastructure, including advanced abstractions and logic.

To manage Kubernetes infrastructure using Pulumi, you will use the Pulumi Kubernetes SDK. The SDK provides a set of strongly-typed abstractions for creating and managing Kubernetes resources.

Installing the Kubernetes SDK

To get started with Pulumi and Kubernetes, you will need to install the Pulumi CLI and the Pulumi Kubernetes SDK:

curl -fsSL https://get.pulumi.com | sh
npm install @pulumi/kubernetes

Creating a Kubernetes cluster with Pulumi

To create a Kubernetes cluster with Pulumi, you will first define the infrastructure resources you need using the Pulumi Kubernetes SDK. This will typically include:

• A Kubernetes Cluster resource to define the cluster itself
• A set of Node resources to define the worker nodes in your cluster
• Any additional Kubernetes resources you need to configure, such as a kube-proxy or Kubernetes Dashboard addon

Here is an example Pulumi program that creates a Kubernetes cluster:

import * as k8s from "@pulumi/kubernetes";

const myCluster = new k8s.core.v1.Namespace("my-cluster");
const myClusterRoleBinding = new k8s.rbac.v1.ClusterRoleBinding("my-cluster-admin", {
    roleRef: {
        apiGroup: "rbac.authorization.k8s.io",
        kind: "ClusterRole",
        name: "cluster-admin"
    },
    subjects: [{
        kind: "User",
        name: "my-user@example.com"
    }]
});

const myClusterSpec = {
    type: "GKE",
    name: "my-cluster",
    location: "us-central1",
    nodeCount: 3,
    nodeMachineType: "n1-standard-1",
    nodeDiskSizeGb: 100,
    nodeOauthScopes: [
        "cloud-platform"
    ]
};

const myClusterProvider = new k8s.Provider("my-cluster-provider", {
    kubeconfig: config.kubeConfig
});

const myClusterResource = new k8s.GKECluster("my-cluster", myClusterSpec, {
    provider: myClusterProvider
});

const myNodePoolSpec = {
    name: "my-pool",
    nodeCount: 3,
    nodeMachineType: "n1-standard-1",
    nodeDiskSizeGb: 100
};

const myNodePool = new k8s.GKENodePool("my-node-pool", {
    cluster: myClusterResource.name,
    ...myNodePoolSpec
}, {
    provider: myClusterProvider
});

const nginxService = new k8s.core.v1.Service("nginx", {
    metadata: {
        name: "nginx"
    },
    spec: {
        ports: [{port: 80, targetPort: 80}],
        selector: {
            app: "nginx"
        },
        type: "LoadBalancer"
    }
}, {
    provider: myClusterProvider
});

In this program, we define a Kubernetes Cluster and NodePool resource to create a new Kubernetes cluster with three worker nodes. We also define a Kubernetes Service resource to expose an nginx service on port 80.

Managing Kubernetes resources with Pulumi

Once you have created your Kubernetes cluster with Pulumi, you can then define additional Kubernetes resources using the Pulumi Kubernetes SDK. This might include things like:

• Deployments and ReplicaSets to manage the scaling and rollout of your containerized applications
• Services and Ingresses to manage network traffic to your applications
• ConfigMaps and Secrets to manage application configuration and secrets

Here is an example Pulumi program that deploys a simple nginx application to our Kubernetes cluster:

import * as k8s from "@pulumi/kubernetes";

const nginxDeployment = new k8s.apps.v1.Deployment("nginx", {
    metadata: {name: "nginx"},
    spec: {
        selector: {matchLabels: {app: "nginx"}},
        replicas: 3,
        template: {
            metadata: {labels: {app: "nginx"}},
            spec: {
                containers: [{
                    name: "nginx",
                    image: "nginx:latest",
                    ports: [{name: "http", containerPort: 80}]
                }]
            }
        }
    }
}, {provider: myClusterProvider});

In this program, we define a Kubernetes Deployment resource to deploy an nginx application with three replicas to our Kubernetes cluster.

Managing dependencies with Pulumi

Like Terraform, Pulumi provides several mechanisms for managing dependencies between different pieces of infrastructure. You can use dependsOn to explicitly specify dependencies between resources or use variables to pass data between resources.

Using Amazon CDK to manage Kubernetes

Amazon CDK is an IaC tool that allows you to write infrastructure code in familiar programming languages such as TypeScript, Python, Java, and C#. CDK provides a set of high-level abstractions that allow you to define cloud resources in a programmatic way.

To manage Kubernetes infrastructure using Amazon CDK, you will use the AWS Cloud Development Kit (CDK) for Kubernetes. The CDK provides a set of types that map directly to Kubernetes resources and allows you to define them using your preferred programming language.

Installing the CDK for Kubernetes

To get started with the CDK for Kubernetes, you will need to install the AWS CDK CLI and the AWS CDK for Kubernetes library:

npm install -g aws-cdk
npm install aws-cdk-lib aws-cdk-lib-eks aws-cdk-lib-k8s

Creating a Kubernetes cluster with CDK

To create a Kubernetes cluster with the CDK, you will define the infrastructure resources you need using the AWS CDK and CDK for Kubernetes libraries. This will typically include:

• A Kubernetes cluster resource to define the cluster itself
• A set of node resources to define the worker nodes in your cluster
• Any additional Kubernetes resources you need to configure, such as a kube-proxy or Kubernetes Dashboard addon

Here is an example CDK program that creates a Kubernetes cluster:

import * as eks from "aws-cdk-lib/aws-eks";
import * as k8s from "aws-cdk-lib/k8s";

const myCluster = new eks.Cluster(this, "my-cluster", {
    clusterName: "my-cluster",
    version: eks.KubernetesVersion.V1_21,
    defaultCapacity: 3,
    defaultCapacityInstance: new ec2.InstanceType("t3.large")
});

const myNodeGroup = myCluster.addCapacity("my-node-group", {
    instanceType: new ec2.InstanceType("t3.large"),
    minCapacity: 1,
    maxCapacity: 3
});

const nginxService = new k8s.Service(this, "nginx", {
    metadata: {name: "nginx"},
    spec: {
        ports: [{port: 80, targetPort: 80}],
        selector: {
            app: "nginx"
        },
        type: "LoadBalancer"
    }
});

In this program, we define an EKS Cluster and NodeGroup to create a new Kubernetes cluster with three worker nodes. We also define a Kubernetes Service resource to expose an nginx service on port 80.

Managing Kubernetes resources with CDK

Once you have created your Kubernetes cluster with the CDK, you can then define additional Kubernetes resources using the CDK for Kubernetes library. This might include things like:

• Deployments and ReplicaSets to manage the scaling and rollout of your containerized applications
• Services and Ingresses to manage network traffic to your applications
• ConfigMaps and Secrets to manage application configuration and secrets

Here is an example CDK program that deploys a simple nginx application to our Kubernetes cluster:

import * as k8s from "aws-cdk-lib/k8s";

const nginxDeployment = new k8s.Deployment(this, "nginx", {
    metadata: {name: "nginx"},
    spec: {
        replicas: 3,
        selector: {matchLabels: {app: "nginx"}},
        template: {
            metadata: {labels: {app: "nginx"}},
            spec: {
                containers: [{
                    name: "nginx",
                    image: "nginx:latest",
                    ports: [{name: 'http', containerPort: 80}]
                }]
            }
        }
    }
});

const nginxService = new k8s.Service(this, "nginx", {
    metadata: {name: "nginx"},
    spec: {
        ports: [{port: 80, targetPort: 80}],
        selector: {
            app: "nginx"
        },
        type: "LoadBalancer"
    }
});

In this program, we define a Kubernetes Deployment resource to deploy an nginx application with three replicas to our Kubernetes cluster. We also define a Kubernetes Service resource to expose the nginx service on port 80.

Managing dependencies with CDK

Amazon CDK provides a comprehensive set of features for managing dependencies between resources. You can use dependsOn to specify dependencies between resources, use constructs to encapsulate resources and their dependencies, and leverage CDK's powerful programming abstractions to manage resources dynamically.

Conclusion

By using IaC tools like Terraform, Pulumi, and Amazon CDK to manage your Kubernetes infrastructure, you can automate the creation and management of your infrastructure, ensure that it remains reproducible, scalable, and consistent, and reduce the risk of human error that can come with manual configurations.

Each of these IaC tools provides a unique and powerful way to manage your Kubernetes infrastructure. Whether you prefer the declarative nature of Terraform, the programming-language flexibility of Pulumi, or the comprehensive feature set of Amazon CDK, there is an IaC tool out there that fits your needs.

So go forth, Kubernetes pioneers! Use infrastructure as code to create reliable, scalable, and consistent Kubernetes infrastructure that can withstand the demands of modern containerized applications.

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