Advanced Helm Chart Customization

Prerequisites

Before you begin, check the following prerequisites:

Download the Istio release.
Perform any necessary platform-specific setup.
Check the Requirements for Pods and Services.
Usage of helm for Istio installation.
Helm version that supports post rendering. (>= 3.1)
kubectl or kustomize.

Istio's helm chart tries to incorporate most of the attributes needed by users for their specific requirements. However, it does not contain every possible Kubernetes value you may want to tweak. While it is not practical to have such a mechanism in place, in this document we will demonstrate a method which would allow you to do some advanced helm chart customization without the need to directly modify Istio's helm chart.

Using Helm with kustomize to post-render Istio charts

Using the Helm post-renderer capability, you can tweak the installation manifests to meet your requirements easily. Post-rendering gives the flexibility to manipulate, configure, and/or validate rendered manifests before they are installed by Helm. This enables users with advanced configuration needs to use tools like Kustomize to apply configuration changes without the need for any additional support from the original chart maintainers.

Adding a value to an already existing chart

In this example, we will add a sysctl value to Istio’s ingress-gateway deployment. We are going to:

Create a sysctl deployment customization patch template.
Apply the patch using Helm post-rendering.
Verify that the sysctl patch was correctly applied to the pods.

Create the Kustomization

First, we create a sysctl patch file, adding a securityContext to the ingress-gateway pod with the additional attribute:

{{< text bash >}} $ cat > sysctl-ingress-gw-customization.yaml <<EOF apiVersion: apps/v1 kind: Deployment metadata: name: istio-ingress namespace: istio-ingress spec: template: spec: securityContext: sysctls: - name: net.netfilter.nf_conntrack_tcp_timeout_close_wait value: "10" EOF {{< /text >}}

The below shell script helps to bridge the gap between Helm post-renderer and Kustomize, as the former works with stdin/stdout and the latter works with files.

{{< text bash >}} $ cat > kustomize.sh <<EOF #!/bin/sh cat > base.yaml exec kubectl kustomize # you can also use "kustomize build ." if you have it installed. EOF $ chmod +x ./kustomize.sh {{< /text >}}

Finally, let us create the kustomization yaml file, which is the input for kustomize with the set of resources and associated customization details.

{{< text bash >}} $ cat > kustomization.yaml <<EOF resources:

base.yaml patchesStrategicMerge:
sysctl-ingress-gw-customization.yaml EOF {{< /text >}}

Apply the Kustomization

Now that the Kustomization file is ready, let us use Helm to make sure this gets applied properly.

Add the Helm repository for Istio

{{< text bash >}} $ helm repo add istio https://istio-release.storage.googleapis.com/charts $ helm repo update {{< /text >}}

Render and Verify using Helm Template

We can use Helm post-renderer to validate rendered manifests before they are installed by Helm

{{< text bash >}} $ helm template istio-ingress istio/gateway --namespace istio-ingress --post-renderer ./kustomize.sh | grep -B 2 -A 1 netfilter.nf_conntrack_tcp_timeout_close_wait {{< /text >}}

In the output, check for the newly added sysctl attribute for ingress-gateway pod:

{{< text yaml >}} securityContext: sysctls: - name: net.netfilter.nf_conntrack_tcp_timeout_close_wait value: "10" {{< /text >}}

Apply the patch using Helm `Post-Renderer`

Use the below command to install an Istio ingress-gateway, applying our customization using Helm post-renderer:

{{< text bash >}} $ kubectl create ns istio-ingress $ helm upgrade -i istio-ingress istio/gateway --namespace istio-ingress --wait --post-renderer ./kustomize.sh {{< /text >}}

Verify the Kustomization

Examine the ingress-gateway deployment, you will see the newly manipulated sysctl value:

{{< text bash >}} $ kubectl -n istio-ingress get deployment istio-ingress -o yaml {{< /text >}}

{{< text yaml >}} apiVersion: apps/v1 kind: Deployment metadata: … name: istio-ingress namespace: istio-ingress spec: template: metadata: … spec: securityContext: sysctls: - name: net.netfilter.nf_conntrack_tcp_timeout_close_wait value: "10" {{< /text >}}

Additional Information

For further detailed information about the concepts and techniques described in this document, please refer to:

Advanced Helm Chart Customization

Prerequisites