diff --git a/docs/charts.md b/docs/charts.md index 58b467dc4..5098e0041 100644 --- a/docs/charts.md +++ b/docs/charts.md @@ -451,6 +451,45 @@ directory. **TIP:** _To drop a dependency into your `charts/` directory, use the `helm fetch` command_ +### Operational aspects of using dependencies + +The above sections explain how to specify chart dependencies, but how does this affect +chart installation using `helm install` and `helm upgrade`? + +Suppose that a chart named "A" creates the following Kubernetes objects + +- namespace "A-Namespace" +- statefulset "A-StatefulSet" +- service "A-Service" + +Furthermore, A is dependent on chart B that creates objects + +- namespace "B-Namespace" +- replicaset "B-ReplicaSet" +- service "B-Service" + +After installation/upgrade of chart A a single Helm release is created/modified. The release will +create/update all of the above Kubernetes objects in the following order: + +- A-Namespace +- B-Namespace +- A-StatefulSet +- B-ReplicaSet +- A-Service +- B-Service + +This is because when Helm installs/upgrades charts, +the Kubernetes objects from the charts and all its dependencies are + +- aggregrated into a single set; then +- sorted by type followed by name; and then +- created/updated in that order. + +Hence a single release is created with all the objects for the chart and its dependencies. + +The install order of Kubernetes types is given by the enumeration InstallOrder in kind_sorter.go +(see [the Helm source file](https://github.com/kubernetes/helm/blob/master/pkg/tiller/kind_sorter.go#L26). + ## Templates and Values Helm Chart templates are written in the