Argo CD provides a mechanism to override the parameters of a ksonnet/helm app. This gives some extra flexibility in having most of the application manifests defined in git, while leaving room for some parts of the k8s manifests determined dynamically, or outside of git. It also serves as an alternative way of redeploying an application by changing application parameters via Argo CD, instead of making the changes to the manifests in git.
NOTE: many consider this mode of operation as an anti-pattern to GitOps, since the source of truth becomes a union of the git repository, and the application overrides. The Argo CD parameter overrides feature is provided mainly convenience to developers and is intended to be used more for dev/test environments, vs. production environments.
To use parameter overrides, run the
argocd app set -p (COMPONENT=)PARAM=VALUE command:
argocd app set guestbook -p guestbook=image=example/guestbook:abcd123 argocd app sync guestbook
The following are situations where parameter overrides would be useful:
A team maintains a "dev" environment, which needs to be continually updated with the latest version of their guestbook application after every build in the tip of master. To address this use case, the application would expose an parameter named
image, whose value used in the
devenvironment contains a placeholder value (e.g.
example/guestbook:replaceme). The placeholder value would be determined externally (outside of git) such as a build systems. Then, as part of the build pipeline, the parameter value of the
imagewould be continually updated to the freshly built image (e.g.
argocd app set guestbook -p guestbook=image=example/guestbook:abcd123). A sync operation would result in the application being redeployed with the new image.
A repository of helm manifests is already publicly available (e.g. https://github.com/helm/charts). Since commit access to the repository is unavailable, it is useful to be able to install charts from the public repository, customizing the deployment with different parameters, without resorting to forking the repository to make the changes. For example, to install redis from the helm chart repository and customize the the database password, you would run:
argocd app create redis --repo https://github.com/helm/charts.git --path stable/redis --dest-server https://kubernetes.default.svc --dest-namespace default -p password=abc123