Manage Kubernetes resources via Terraform

Kubernetes (K8S) is an open-source workload scheduler with focus on containerized applications. You can use the Terraform Kubernetes provider to interact with resources supported by Kubernetes.

In this tutorial, you will learn how to interact with Kubernetes using Terraform, by scheduling and exposing a NGINX deployment on a Kubernetes cluster. You will also manage custom resources using Terraform.

The final Terraform configuration files used in this tutorial can be found in the Deploy NGINX on Kubernetes via Terraform GitHub repository.

Why deploy with Terraform?

While you could use kubectl or similar CLI-based tools to manage your Kubernetes resources, using Terraform has the following benefits:

• Unified Workflow - If you are already provisioning Kubernetes clusters with Terraform, use the same configuration language to deploy your applications into your cluster.

• Full Lifecycle Management - Terraform doesn't only create resources, it updates, and deletes tracked resources without requiring you to inspect the API to identify those resources.

• Graph of Relationships - Terraform understands dependency relationships between resources. For example, if a Persistent Volume Claim claims space from a particular Persistent Volume, Terraform won't attempt to create the claim if it fails to create the volume.

Prerequisites

The tutorial assumes some basic familiarity with Kubernetes and kubectl.

It also assumes that you are familiar with the usual Terraform plan/apply workflow. If you're new to Terraform itself, refer first to the Getting Started tutorial.

For this tutorial, you will need an existing Kubernetes cluster. If you don't have a Kubernetes cluster, you can use kind to provision a local Kubernetes cluster or provision one on a cloud provider.

Follow these instructions or choose a package manager based on your operating system to install kind.

$ brew install kind 

$ choco install kind 

Once you've done this, download and save the kind configuration into a file named kind-config.yaml. This configuration adds extra port mappings, so you can access the NGINX service locally later.

$ curl https://raw.githubusercontent.com/hashicorp/learn-terraform-deploy-nginx-kubernetes-provider/main/kind-config.yaml --output kind-config.yaml 

Then, create a kind Kubernetes cluster.

$ kind create cluster --name terraform-learn --config kind-config.yaml Creating cluster "terraform-learn" ...  ✓ Ensuring node image (kindest/node:v1.17.0) 🖼  ✓ Preparing nodes 📦  ✓ Writing configuration 📜  ✓ Starting control-plane 🕹️  ✓ Installing CNI 🔌  ✓ Installing StorageClass 💾 Set kubectl context to "kind-terraform-learn" You can now use your cluster with:  kubectl cluster-info --context kind-terraform-learn  Have a nice day! 👋 

Verify that your cluster exists by listing your kind clusters.

$ kind get clusters terraform-learn 

Then, point kubectl to interact with this cluster. The context is kind- followed by the name of your cluster.

$ kubectl cluster-info --context kind-terraform-learn Kubernetes master is running at https://127.0.0.1:32769 KubeDNS is running at https://127.0.0.1:32769/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy  To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'. 

Configure the provider

Before you can schedule any Kubernetes services using Terraform, you need to configure the Terraform Kubernetes provider.

There are many ways to configure the Kubernetes provider. We recommend them in the following order (most recommended first, least recommended last):

1. Use cloud-specific auth plugins (for example, eks get-token, az get-token, gcloud config)
2. Use oauth2 token
3. Use TLS certificate credentials
4. Use kubeconfig file by setting both config_path and config_context
5. Use username and password (HTTP Basic Authorization)

Follow the instructions in the kind or cloud provider tabs to configure the provider to target a specific Kubernetes cluster. The cloud provider tabs will configure the Kubernetes provider using cloud-specific auth tokens.

Create a directory named learn-terraform-deploy-nginx-kubernetes.

$ mkdir learn-terraform-deploy-nginx-kubernetes 

Then, navigate into it

$ cd learn-terraform-deploy-nginx-kubernetes 

Then, create a new file named kubernetes.tf and add the following configuration to it. This serves as a base configuration for the provider.

terraform {  required_providers {  kubernetes = {  source = "hashicorp/kubernetes"  }  } }  variable "host" {  type = string }  variable "client_certificate" {  type = string }  variable "client_key" {  type = string }  variable "cluster_ca_certificate" {  type = string }  provider "kubernetes" {  host = var.host   client_certificate = base64decode(var.client_certificate)  client_key = base64decode(var.client_key)  cluster_ca_certificate = base64decode(var.cluster_ca_certificate) } 

To properly configure this provider, you need to define the variables.

First, view your kind cluster information.

$ kubectl config view --minify --flatten --context=kind-terraform-learn apiVersion: v1 clusters: - cluster:  certificate-authority-data: LS0tLS1CRU...  server: https://127.0.0.1:32768  name: kind-terraform-learn contexts: - context:  cluster: kind-terraform-learn  user: kind-terraform-learn  name: kind-terraform-learn current-context: kind-terraform-learn kind: Config preferences: {} users: - name: kind-terraform-learn  user:  client-certificate-data: LS0tLS1CRU...  client-key-data: LS0tLS1CRU... 

Define the variables in a terraform.tfvars file.

• host corresponds with clusters.cluster.server.
• client_certificate corresponds with users.user.client-certificate.
• client_key corresponds with users.user.client-key.
• cluster_ca_certificate corresponds with clusters.cluster.certificate-authority-data.

You should end up with something similar to the following.

host = "https://127.0.0.1:32768" client_certificate = "LS0tLS1CRUdJTiB..." client_key = "LS0tLS1CRUdJTiB..." cluster_ca_certificate = "LS0tLS1CRUdJTiB..." 

After configuring the provider, run terraform init to download the latest version and initialize your Terraform workspace.

$ terraform init 

Schedule a deployment

Add the following to your kubernetes.tf file. This Terraform configuration will schedule a NGINX deployment with two replicas on your Kubernetes cluster, internally exposing port 80 (HTTP).

resource "kubernetes_deployment" "nginx" {  metadata {  name = "scalable-nginx-example"  labels = {  App = "ScalableNginxExample"  }  }   spec {  replicas = 2  selector {  match_labels = {  App = "ScalableNginxExample"  }  }  template {  metadata {  labels = {  App = "ScalableNginxExample"  }  }  spec {  container {  image = "nginx:stable-alpine-slim"  name = "example"   port {  container_port = 80  }   resources {  limits = {  cpu = "0.5"  memory = "512Mi"  }  requests = {  cpu = "250m"  memory = "50Mi"  }  }  }  }  }  } } 

You may notice the similarities between the Terraform configuration and Kubernetes configuration YAML file.

Apply the configuration to schedule the NGINX deployment. Confirm your apply with a yes.

$ terraform apply  Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:  + create  Terraform will perform the following actions:   # kubernetes_deployment.nginx will be created  + resource "kubernetes_deployment" "nginx" {  ## ...  }  Plan: 1 to add, 0 to change, 0 to destroy.  Do you want to perform these actions?  Terraform will perform the actions described above.  Only 'yes' will be accepted to approve.   Enter a value: yes  kubernetes_deployment.nginx: Creating... kubernetes_deployment.nginx: Still creating... [10s elapsed] kubernetes_deployment.nginx: Still creating... [20s elapsed] kubernetes_deployment.nginx: Creation complete after 26s [id=default/scalable-nginx-example]  Apply complete! Resources: 1 added, 0 changed, 0 destroyed. 

Once the apply is complete, verify the NGINX deployment is running.

$ kubectl get deployments NAME READY UP-TO-DATE AVAILABLE AGE scalable-nginx-example 2/2 2 2 15s 

Schedule a Service

There are multiple Kubernetes services you can use to expose your NGINX to users.

If your Kubernetes cluster is hosted locally on kind, you will expose your NGINX instance via NodePort to access your instance. This exposes the service on each node's IP at a static port, allowing you to access the service from outside the cluster at <NodeIP>:<NodePort>.

If your Kubernetes cluster is hosted on a cloud provider, you will expose your NGINX instance via LoadBalancer to access your instance. This exposes the service externally using a cloud provider's load balancer.

Notice how the Kubernetes Service resource block dynamically assigns the selector to the Deployment's label. This avoids common bugs due to mismatched service label selectors.

Add the following configuration to your kubernetes.tf file. This will expose the NGINX instance at the node_port: 30201.

resource "kubernetes_service" "nginx" {  metadata {  name = "nginx-example"  }  spec {  selector = {  App = kubernetes_deployment.nginx.spec.0.template.0.metadata[0].labels.App  }  port {  node_port = 30201  port = 80  target_port = 80  }   type = "NodePort"  } } 

Apply the configuration to schedule the NodePort Service. Confirm your apply with a yes.

$ terraform apply kubernetes_deployment.nginx: Refreshing state... [id=default/scalable-nginx-example]  ## ...  Plan: 1 to add, 0 to change, 0 to destroy.  Do you want to perform these actions?  Terraform will perform the actions described above.  Only 'yes' will be accepted to approve.   Enter a value: yes  kubernetes_service.nginx: Creating... kubernetes_service.nginx: Creation complete after 0s [id=default/nginx-example]  Apply complete! Resources: 1 added, 0 changed, 0 destroyed. 

Once the apply is complete, verify the NGINX service is running.

$ kubectl get services NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 2m53s nginx-example NodePort 10.96.55.64 <none> 80:30201/TCP 76s 

You can access the NGINX instance by navigating to the NodePort at http://localhost:30201/.

Scale the deployment

You can scale your deployment by increasing the replicas field in your configuration. Change the number of replicas in your Kubernetes deployment from 2 to 4.

resource "kubernetes_deployment" "nginx" {  ## ...   spec {  replicas = 4   ## ...  }   ## ... } 

Apply the change to scale your deployment. Confirm your apply with a yes.

$ terraform apply kubernetes_deployment.nginx: Refreshing state... [id=default/scalable-nginx-example] kubernetes_service.nginx: Refreshing state... [id=default/nginx-example]  ## ...  Plan: 0 to add, 1 to change, 0 to destroy.  Do you want to perform these actions?  Terraform will perform the actions described above.  Only 'yes' will be accepted to approve.   Enter a value: yes  kubernetes_deployment.nginx: Modifying... [id=default/scalable-nginx-example] kubernetes_deployment.nginx: Modifications complete after 0s [id=default/scalable-nginx-example]  Apply complete! Resources: 0 added, 1 changed, 0 destroyed. 

Once the apply is complete, verify the NGINX deployment has four replicas.

$ kubectl get deployments NAME READY UP-TO-DATE AVAILABLE AGE scalable-nginx-example 4/4 4 4 4m48s 

Managing Custom Resources

In addition to built-in resources and data sources, the Terraform provider also includes a kubernetes_manifest resource that lets you manage custom resource definitions (CRDs), custom resources, or any resource that is not built into the Terraform provider.

You will use Terraform to apply a CRD then manage custom resources. You have to do this in two steps:

1. Apply the required CRD to the cluster
2. Apply the Custom Resources to the cluster

You need two apply steps because at plan time Terraform queries the Kubernetes API to verify the schema for the kind of object specified in the manifest field. If Terraform doesn't find the CRD for the resource defined in the manifest the plan will return an error.

Create a custom resource definition

Create a new file named crontab_crd.tf and paste in the bellow configuration for a CRD that extends Kubernetes to store cron data as a resource called CronTab.

resource "kubernetes_manifest" "crontab_crd" {  manifest = {  "apiVersion" = "apiextensions.k8s.io/v1"  "kind" = "CustomResourceDefinition"  "metadata" = {  "name" = "crontabs.stable.example.com"  }  "spec" = {  "group" = "stable.example.com"  "names" = {  "kind" = "CronTab"  "plural" = "crontabs"  "shortNames" = [  "ct",  ]  "singular" = "crontab"  }  "scope" = "Namespaced"  "versions" = [  {  "name" = "v1"  "schema" = {  "openAPIV3Schema" = {  "properties" = {  "spec" = {  "properties" = {  "cronSpec" = {  "type" = "string"  }  "image" = {  "type" = "string"  }  }  "type" = "object"  }  }  "type" = "object"  }  }  "served" = true  "storage" = true  },  ]  }  } } 

The resource has two configurable fields: cronSpec and image. Apply the configuration to create the CRD. Confirm your apply with yes.

$ terraform apply  Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:  + create  Terraform will perform the following actions:   # kubernetes_manifest.crontab_crd will be created  + resource "kubernetes_manifest" "crontab_crd" {  + manifest = {  # ...  }  + object = {  # ...  }  }  Plan: 1 to add, 0 to change, 0 to destroy.  Do you want to perform these actions?  Terraform will perform the actions described above.  Only 'yes' will be accepted to approve.   Enter a value: yes  kubernetes_manifest.crontab_crd: Creating... kubernetes_manifest.crontab_crd: Creation complete after 0s  Apply complete! Resources: 1 added, 0 changed, 0 destroyed. 

Note that in the plan, Terraform created a resource with two attributes: manifest and object.

1. The manifest attribute is your desired configuration, and object is the end state returned by the Kubernetes API server after Terraform created the resource.
2. The object attribute contains many more fields than you specified in manifest because Terraform generated a schema containing all of the possible resource attributes that the Kubernetes API server could add. When referencing the kubernetes_manifest resource from outputs or other resources, always use the object attribute.

Confirm that Terraform created the CRD using kubectl.

$ kubectl get crds crontabs.stable.example.com NAME CREATED AT crontabs.stable.example.com 2022-04-11T15:53:41Z 

The contrabs resource definition now exists in Kubernetes, but you have not used it to define any Kubernetes resources yet. Check for the resource definition with kubectl, which would return error: the server doesn't have a resource type "crontab" if the CRD didn't exist.

$ kubectl get crontabs  No resources found in default namespace. 

Create a custom resource

Now, create a new file named my_new_crontab.tf and paste in the following configuration, which creates a custom resource based on your newly created CronTab CRD.

resource "kubernetes_manifest" "my_new_crontab" {  manifest = {  "apiVersion" = "stable.example.com/v1"  "kind" = "CronTab"  "metadata" = {  "name" = "my-new-cron-object"  "namespace" = "default"  }  "spec" = {  "cronSpec" = "* * * * */5"  "image" = "my-awesome-cron-image"  }  } } 

Apply the configuration to create the custom resource. Confirm the apply with yes.

$ terraform apply  Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:  + create  Terraform will perform the following actions:   # kubernetes_manifest.my_new_crontab will be created  + resource "kubernetes_manifest" "my_new_crontab" {  + manifest = {  + apiVersion = "stable.example.com/v1"  + kind = "CronTab"  + metadata = {  + name = "my-new-cron-object"  + namespace = "default"  }  + spec = {  + cronSpec = "* * * * */5"  + image = "my-awesome-cron-image"  }  }  + object = {  + apiVersion = "stable.example.com/v1"  + kind = "CronTab"  + metadata = {  # ...  }  + spec = {  + cronSpec = "* * * * */5"  + image = "my-awesome-cron-image"  }  }  }  Plan: 1 to add, 0 to change, 0 to destroy.  Do you want to perform these actions?  Terraform will perform the actions described above.  Only 'yes' will be accepted to approve.   Enter a value: yes  kubernetes_manifest.my_new_crontab: Creating... kubernetes_manifest.my_new_crontab: Creation complete after 0s  Apply complete! Resources: 1 added, 0 changed, 0 destroyed. 

Confirm that Terraform created the custom resource.

$ kubectl get crontabs NAME AGE my-new-cron-object 5m37s 

View the new custom resource.

$ kubectl describe crontab my-new-cron-object Name: my-new-cron-object Namespace: default Labels: <none> Annotations: <none> API Version: stable.example.com/v1 Kind: CronTab Metadata:  Creation Timestamp: 2022-04-11T16:07:40Z  Generation: 1  Managed Fields:  API Version: stable.example.com/v1  Fields Type: FieldsV1  fieldsV1:  f:spec:  f:cronSpec:  f:image:  Manager: Terraform  Operation: Apply  Time: 2022-04-11T16:07:40Z  Resource Version: 2432053  UID: 6dd859fc-8665-44ae-91f7-959cff8712b1 Spec:  Cron Spec: * * * * */5  Image: my-awesome-cron-image Events: <none> 

Clean up your workspace

Destroy any resources you created once you're done with this tutorial.

Running terraform destroy will de-provision the NGINX deployment and service you created in this tutorial. Confirm your destroy with a yes.

$ terraform destroy kubernetes_deployment.nginx: Refreshing state... [id=default/scalable-nginx-example] kubernetes_service.nginx: Refreshing state... [id=default/nginx-example]  ## ...  Plan: 0 to add, 0 to change, 2 to destroy.  Do you really want to destroy all resources?  Terraform will destroy all your managed infrastructure, as shown above.  There is no undo. Only 'yes' will be accepted to confirm.   Enter a value: yes  kubernetes_service.nginx: Destroying... [id=default/nginx-example] kubernetes_service.nginx: Destruction complete after 0s kubernetes_deployment.nginx: Destroying... [id=default/scalable-nginx-example] kubernetes_deployment.nginx: Destruction complete after 0s  Destroy complete! Resources: 2 destroyed. 

If you are using a kind Kubernetes cluster, run the following command to delete it.

$ kind delete cluster --name terraform-learn 

If you followed a previous tutorial to set up a Kubernetes cluster, refer to the "Cleaning up your workspace" section of the tutorial to remove those resources as well. Otherwise, your Kubernetes cluster will remain running.

Next steps

In this tutorial, you configured the Terraform Kubernetes provider and used it to schedule, expose and scale an NGINX instance. You also used Terraform to create a custom resource definition and manage a custom resource.

To discover additional capabilities, visit the Terraform Kubernetes Provider Registry Documentation Page.

For a more in-depth Kubernetes examples, complete the Deploy Consul and Vault on a Kubernetes Cluster using Run Triggers (runs on Google Cloud Platform) and Manage Kubernetes Custom Resources tutorials.