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Health checking your apps in a Yandex Managed Service for Kubernetes cluster using a Yandex Application Load Balancer L7 load balancer

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Updated at December 18, 2024

You can use the Application Load Balancer Ingress controller to automatically health check your applications deployed in a Managed Service for Kubernetes cluster.

An Ingress controller installed in the cluster deploys an L7 load balancer with all the required Application Load Balancer resources based on the configuration of the Ingress and HttpBackendGroup resources you created.

The L7 load balancer automatically health checks the application in this cluster. Depending on the results, the L7 load balancer allows or denies external traffic to the backend (Service resource). For more information, see Health checks.

By default, the Application Load Balancer Ingress controller receives application health check requests from the L7 load balancer on TCP port 10501 and health checks the kube-proxy pods on each cluster node. If kube-proxy is healthy, then, even if an application in a particular pod does not respond, Kubernetes will redirect traffic to a different pod with that application or to a different node.

In this tutorial, you will configure your own application health checks using the HttpBackendGroup resource parameters and open a dedicated port on cluster nodes for these checks in the NodePort type Service resource parameters.

You can view health check results in the management console.

Note

You can also configure application health checks using the ingress.alb.yc.io/health-checks annotation of the Service resource.

To deploy an application in a Managed Service for Kubernetes cluster and configure access to it and health checks via an Application Load Balancer L7 load balancer:

  1. Prepare your cloud.
  2. Create a Docker image.
  3. Deploy a test application.
  4. Prepare an address for the L7 load balancer.
  5. Create the Ingress and HttpBackendGroup resources.
  6. Check the result.

If you no longer need the resources you created, delete them.

Prepare your cloud

Prepare the infrastructure

  1. Create security groups for the Managed Service for Kubernetes cluster and its node groups.

    Also configure the security groups required for Application Load Balancer.

    The application will be available on the Managed Service for Kubernetes cluster nodes on port 30080. Application health checks will be available on port 30081. Make sure these ports are open for the L7 load balancer in the node group's security group. You can also make these ports internet-accessible.

    Warning

    The configuration of security groups determines the performance and availability of the cluster and the services and applications running in it.

  2. Create a Managed Service for Kubernetes cluster. When creating it, specify the security groups prepared in advance.

    If you intend to use your cluster within the Yandex Cloud network, there is no need to allocate a public IP address to it. To allow connections from outside the network, assign a public IP address to the cluster.

  3. Create a node group. Allocate it a public IP address to provide internet access and allow pulling Docker images and components. Specify the security groups prepared in advance.

  4. Create a registry in Yandex Container Registry.

  1. If you do not have Terraform yet, install it.

  2. Get the authentication credentials. You can add them to environment variables or specify them later in the provider configuration file.

  3. Configure and initialize a provider. There is no need to create a provider configuration file manually, you can download it.

  4. Place the configuration file in a separate working directory and specify the parameter values. If you did not add the authentication credentials to environment variables, specify them in the configuration file.

  5. Download the k8s-custom-health-checks.tf configuration file to the same working directory.

    This file describes:

    • Network.
    • Subnet.
    • Security groups required for the Managed Service for Kubernetes cluster, node group, and the Application Load Balancer load balancer.
    • Service account required for the Kubernetes cluster.
    • Kubernetes cluster.
    • Kubernetes node group.
    • Registry in Yandex Container Registry.

  6. Specify the following in the k8s-custom-health-checks.tf file:

    • folder_id: Cloud folder ID, same as in the provider settings.
    • k8s_version: Kubernetes version. Available versions are listed in Release channels.

  7. Check that the Terraform configuration files are correct using this command:

    terraform validate

    If there are any errors in the configuration files, Terraform will point them out.

  8. Create the required infrastructure:

    1. Run the command to view planned changes:

      terraform plan

      If the resource configuration descriptions are correct, the terminal will display a list of the resources to modify and their parameters. This is a test step. No resources are updated.

    2. If you are happy with the planned changes, apply them:

      1. Run the command:

        terraform apply

      2. Confirm the update of resources.

      3. Wait for the operation to complete.

    All the required resources will be created in the specified folder. You can check resource availability and their settings in the management console.

Install the Application Load Balancer Ingress controller

Use this guide to install the ALB Ingress Controller application in a separate yc-alb namespace. Later on, all the required Kubernetes resources will be created in this namespace.

Install additional dependencies

  1. If you do not have the Yandex Cloud command line interface yet, install and initialize it.

    The folder specified in the CLI profile is used by default. You can specify a different folder using the --folder-name or --folder-id parameter.

  2. Install kubectl and configure it to work with the created cluster.

    If a cluster has no public IP address assigned and kubectl is configured via the cluster's private IP address, run kubectl commands on a Yandex Cloud VM that is in the same network as the cluster.

  3. Install Docker.

  4. Authenticate in Yandex Container Registry using a Docker credential helper.

Create a Docker image

The source files for a Docker image reside in the yc-mk8s-alb-ingress-health-checks repository.

The Docker image will be created from app/Dockerfile and will contain test application code from the app/healthchecktest.go file. You will use this Docker image to deploy the application in your Managed Service for Kubernetes cluster.

The application will respond to HTTP requests as follows depending on the pod port:

  • 80: Return request path parameters in the response body, e.g., /test-path. This is the main functionality of the application that will be available via the L7 load balancer.
  • 8080: Return an OK message in the response body. This functionality will be used to perform application health checks.

Successful requests will return the 200 OK HTTP code.

To create a Docker image:

  1. Clone the yc-mk8s-alb-ingress-health-checks repository:

    git clone git@github.com:yandex-cloud-examples/yc-mk8s-alb-ingress-health-checks.git

  2. In the terminal, go to the root of the repository directory.

  3. Get the Container Registry registry ID. You can request it with a list of registries in the folder.

  4. In the environment variable, add the name of the Docker image to create:

    export TEST_IMG=cr.yandex/<registry_ID>/example-app1:latest

  5. Build the Docker image:

    docker build -t ${TEST_IMG} -f ./app/Dockerfile .

    The command specifies the path for the repository's root directory.

  6. Push the Docker image to the registry:

    docker push ${TEST_IMG}

    If you fail to push the image, follow these steps:

Deploy a test application

Build a test application from the created Docker image and the app/testapp.yaml configuration file.

The file contains the description of Kubernetes resources: Deployment and Service of the NodePort type.

The Service resource contains the description of ports used to access the application on your cluster's nodes:

  • spec.ports.name: http: Port to access the main functionality of the application, 80 on the pod and 30080 on the host.
  • spec.ports.name: health: Port for application health checks, 8080 on the pod and 30081 on the host.

To build a test application:

  1. Specify the value of the TEST_IMG environment variable in the spec.template.spec.containers.image field in the app/testapp.yaml file. To get this value, run:

    printenv TEST_IMG

  2. Create the application from the app/testapp.yaml file:

    kubectl apply -f ./app/testapp.yaml --namespace=yc-alb

    The command specifies the path for the repository's root directory.

  3. Make sure the pods with the application are running:

    kubectl get po --namespace=yc-alb

    Result:

    NAME                               READY   STATUS    RESTARTS   AGE
alb-demo-1-54b95979b4-***          1/1     Running   0          71s
alb-demo-1-54b95979b4-***          1/1     Running   0          71s
yc-alb-ingress-controller-***      1/1     Running   0          11m
yc-alb-ingress-controller-hc-***   1/1     Running   0          11m

  4. Test the application by specifying the IP address of the Managed Service for Kubernetes cluster node in the request. You can find out the IP address of the node in the management console.

    • Main functionality:

      curl --include http://<node_IP_address>:30080/test-path

      Result:

      HTTP/1.1 200 OK
Date: Thu, 18 Jul 2024 11:55:52 GMT
Content-Length: 10
Content-Type: text/plain; charset=utf-8

/test-path%

    • Application health check:

      curl --include http://<node_IP_address>:30081

      Result:

      HTTP/1.1 200 OK
Date: Thu, 18 Jul 2024 12:00:57 GMT
Content-Length: 2
Content-Type: text/plain; charset=utf-8

OK%

Prepare an address for the L7 load balancer

This address will be used to access the application from the internet.

To prepare an address for the load balancer:

  1. Reserve a static public IP address for the Application Load Balancer load balancer.

  2. Register a public domain zone and delegate your domain.

  3. To bind the address to the domain, create an A record for the delegated domain. Specify the reserved IP address as the record value.

  4. Make sure the A record is added:

    host <domain>

    Result:

    <domain> has address <IP_address>

  1. Place the address-for-k8s-health-checks.tf configuration file in the same working directory as the k8s-custom-health-checks.tf file.

    The address-for-k8s-health-checks.tf file describes:

  2. Check that the Terraform configuration files are correct using this command:

    terraform validate

    If there are any errors in the configuration files, Terraform will point them out.

  3. Create the required infrastructure:

    1. Run the command to view planned changes:

      terraform plan

      If the resource configuration descriptions are correct, the terminal will display a list of the resources to modify and their parameters. This is a test step. No resources are updated.

    2. If you are happy with the planned changes, apply them:

      1. Run the command:

        terraform apply

      2. Confirm the update of resources.

      3. Wait for the operation to complete.

    All the required resources will be created in the specified folder. You can check resource availability and their settings in the management console.

  4. Make sure the A record is added:

    host <domain>

    Result:

    <domain> has address <IP_address>

Create the Ingress and HttpBackendGroup resources

Based on the Ingress and HttpBackendGroup resources, the Ingress controller will deploy the L7 load balancer with all the required Application Load Balancer resources.

The ingress.yaml and httpbackendgroup.yaml configuration files for the specified resources are located in the yc-mk8s-alb-ingress-health-checks repository.

You can specify the settings for custom application health checks in the HttpBackendGroup resource in the spec.backends.healthChecks parameter.

To create resources:

  1. In the ingress.yaml file, specify the following values for annotations:

    • ingress.alb.yc.io/subnets: One or more subnets to host the Application Load Balancer L7 load balancer.
    • ingress.alb.yc.io/security-groups: One or more security groups for the load balancer. If you skip this parameter, the default security group will be used. At least one of the security groups must allow an outgoing TCP connection to port 10501 in the Managed Service for Kubernetes node group subnet or to its security group.
    • ingress.alb.yc.io/external-ipv4-address: Public access to the load balancer from the internet. Specify the previously reserved static public IP address.

  2. In the same ingress.yaml file, specify the delegated domain in the spec.rules.host parameter.

  3. To create the Ingress and HttpBackendGroup resources, run the following command from the root of the repository directory:

    kubectl apply -f ingress.yaml --namespace=yc-alb &&
kubectl apply -f httpbackendgroup.yaml --namespace=yc-alb

  4. Wait until the resources are created and the load balancer is deployed and assigned a public IP address. This may take a few minutes.

    To follow the load balancer's creation and make sure it is error-free, open the logs of the pod the creation process was run in:

    1. In the management console, go to the folder page and select Managed Service for Kubernetes.

    2. Click your cluster's name and select Workload in the left-hand panel.

    3. Select the yc-alb-ingress-controller-* pod (not yc-alb-ingress-controller-hc-*) where the resource creation process is running.

    4. Go to the Logs tab on the pod page.

      The load balancer's creation logs are generated and displayed in real time. Any errors that occur will also be logged.

Check the result

  1. Make sure the load balancer was created. To do this, run the appropriate command and check that the command output shows the following value in the ADDRESS field:

    kubectl get ingress alb-demo --namespace=yc-alb

    Result:

    NAME       CLASS    HOSTS     ADDRESS      PORTS   AGE
alb-demo   <none>   <domain>   <IP_address>   80      15h

  2. Check that the deployed application is available via the L7 load balancer:

    curl --include http://<domain>/test-path

    Result:

    HTTP/1.1 200 OK
date: Thu, 18 Jul 2024 12:23:51 GMT
content-length: 10
content-type: text/plain; charset=utf-8
server: ycalb

/test-path%

    Note

    If the resource is unavailable at the specified URL, make sure that the security groups for the Managed Service for Kubernetes cluster and its node groups are configured correctly. If any rule is missing, add it.

  3. Make sure the app health checks are working correctly:

    1. In the management console, go to the folder page and select Application Load Balancer.
    2. Click the load balancer name and select Health checks in the left-hand panel.
    3. Check the target health statuses. The HEALTHY status indicates the application is up and running.

Delete the resources you created

Some resources are not free of charge. Delete the resources you no longer need to avoid paying for them:

  1. Application Load Balancer L7 load balancer
  2. Application Load Balancer HTTP router
  3. Application Load Balancer backend groups
  4. Application Load Balancer target group
  5. Managed Service for Kubernetes node group
  6. Managed Service for Kubernetes cluster
  7. Registry in Container Registry
  8. Cloud DNS public domain zone
  9. Virtual Private Cloud security groups
  10. Virtual Private Cloud static public IP address
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