Advanced Helm Chart Customization
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.
Advanced Helm Chart Customization
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
sysctldeployment customization patch template.
- Apply the patch using Helm
- Verify that the
sysctlpatch 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:
$ 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
The below shell script helps to bridge the gap between Helm
post-renderer and Kustomize, as the former works with
and the latter works with files.
$ 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
Finally, let us create the
kustomization yaml file, which is the input for
with the set of resources and associated customization details.
$ cat > kustomization.yaml <<EOF resources: - base.yaml patchesStrategicMerge: - sysctl-ingress-gw-customization.yaml EOF
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
$ helm repo add istio https://istio-release.storage.googleapis.com/charts $ helm repo update
Render and Verify using Helm Template
We can use Helm
post-renderer to validate rendered manifests before they are installed by Helm
$ 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
In the output, check for the newly added
sysctl attribute for
securityContext: sysctls: - name: net.netfilter.nf_conntrack_tcp_timeout_close_wait value: "10"
Apply the patch using Helm
Use the below command to install an Istio ingress-gateway, applying our customization using Helm
$ kubectl create ns istio-ingress $ helm upgrade -i istio-ingress istio/gateway --namespace istio-ingress --wait --post-renderer ./kustomize.sh
Verify the Kustomization
Examine the ingress-gateway deployment, you will see the newly manipulated
$ kubectl -n istio-ingress get deployment istio-ingress -o 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"
For further detailed information about the concepts and techniques described in this document, please refer to: