Demo: multi namespaces with a common base

kustomize supports defining multiple variants with different namespace, as overlays on a common base.

It's possible to create an additional overlay to compose these variants together - just declare the overlays as the bases of a new kustomization. The following demonstrates this using a base that's just one pod.

Define a place to work:

DEMO_HOME=$(mktemp -d)

Define a common base:

BASE=$DEMO_HOME/base
mkdir $BASE

cat <<EOF >$BASE/kustomization.yaml
resources:
- pod.yaml
EOF

cat <<EOF >$BASE/pod.yaml
apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    app: myapp
spec:
  containers:
  - name: nginx
    image: nginx:1.7.9
EOF

Define a variant in namespace-a overlaying base:

NSA=$DEMO_HOME/namespace-a
mkdir $NSA

cat <<EOF >$NSA/kustomization.yaml
bases:
- ../base
resources:
- namespace.yaml
namespace: namespace-a
EOF

cat <<EOF >$NSA/namespace.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: namespace-a
EOF

Define a variant in namespace-b overlaying base:

NSB=$DEMO_HOME/namespace-b
mkdir $NSB

cat <<EOF >$NSB/kustomization.yaml
bases:
- ../base
resources:
- namespace.yaml
namespace: namespace-b
EOF

cat <<EOF >$NSB/namespace.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: namespace-b
EOF

Then define a Kustomization composing two variants together:

cat <<EOF >$DEMO_HOME/kustomization.yaml
bases:
- namespace-a
- namespace-b
EOF

Now the workspace has following directories

.
├── base
│   ├── kustomization.yaml
│   └── pod.yaml
├── kustomization.yaml
├── namespace-a
│   ├── kustomization.yaml
│   └── namespace.yaml
└── namespace-b
    ├── kustomization.yaml
    └── namespace.yaml

Confirm that the kustomize build output contains two pod objects from namespace-a and namespace-b.

test 2 == \
  $(kustomize build $DEMO_HOME| grep -B 4 "namespace: namespace-[ab]" | grep "name: myapp-pod" | wc -l); \
  echo $?