helm's dry-run mode to render yaml files without applying them

kubernetes helm yaml dry-run helm chart

2 min read | by Jordi Prats

When you are installing or upgrading a helm chart sometimes feels like an act of faith: You don't really know what it's going to actually deploy. With the --dry-run option

We can add the --dry-run option to the install and upgrade commands so we can get the yaml files that it's going to render and apply to the kubernetes cluster, but without actually applying them. This is how it's going to look like:

$ helm upgrade pet2cattle -f pet2cattle_values.yaml . --dry-run
Release "pet2cattle" has been upgraded. Happy Helming!
NAME: pet2cattle
LAST DEPLOYED: Wed Dec 30 10:58:42 2020
NAMESPACE: kube-system
STATUS: pending-upgrade
REVISION: 59
TEST SUITE: None
HOOKS:
MANIFEST:
---
# Source: pet2cattle/charts/minio/templates/post-install-prometheus-metrics-serviceaccount.yaml
apiVersion: v1
kind: ServiceAccount
metadata:
  name: pet2cattle-minio-update-prometheus-secret
  labels:
    app: minio-update-prometheus-secret
    chart: minio-8.0.8
    release: pet2cattle
    heritage: Helm
---
(...)
---
# Source: pet2cattle/templates/22-ingress_https.yaml
apiVersion: networking.k8s.io/v1beta1
kind: Ingress
metadata:
  name: pet2cattle-https
  labels:
    helm.sh/chart: pet2cattle-1
    app.kubernetes.io/name: pet2cattle
    app.kubernetes.io/instance: pet2cattle
    app.kubernetes.io/version: "2.6"
    app.kubernetes.io/managed-by: Helm
  annotations:
    cert-manager.io/cluster-issuer: letsencrypt
    traefik.ingress.kubernetes.io/router.tls: "true"
spec:
  tls:
    - hosts:
        - "pet2cattle.com"
      secretName: k3s-p2c
  rules:
    - host: "pet2cattle.com"
      http:
        paths:
          - backend:
              serviceName: pet2cattle
              servicePort: 8000
    - host: "www.pet2cattle.com"
      http:
        paths:
          - backend:
              serviceName: pet2cattle
              servicePort: 8000

NOTES:
1. Get the application URL by running these commands:

As you can see there is some other data that it's also rendered, so it's not something we can just pipe directly to kubectl diff but with some grep-ing we work it out

Posted on 08/01/2021

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