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Patching multiple resources at once.

kustomize supports patching via either a strategic merge patch (wherein you partially re-specify the thing you want to modify, with in-place changes) or a JSON patch (wherein you specify specific operation/target/value tuples in a particular syntax).

A kustomize file lets one specify many patches. Each patch must be associated with a target selector:

patches:
  - path: <relative path to file containing patch>
    target:
      group: <optional group>
      version: <optional version>
      kind: <optional kind>
      name: <optional name or regex pattern>
      namespace: <optional namespace>
      labelSelector: <optional label selector>
      annotationSelector: <optional annotation selector>

E.g. select resources with name matching the regular expression foo.*:

target:
  name: foo.*

Select all resources of kind Deployment:

target:
  kind: Deployment

Using multiple fields just makes the target more specific. The following selects only Deployments that also have the label app=hello (full label/annotation selector rules):

target:
  kind: Deployment
  labelSelector: app=hello

Demo

The example below shows how to inject a sidecar container for multiple Deployment resources.

Make a place to work:

DEMO_HOME=$(mktemp -d)

Make a file describing two Deployments:

cat <<EOF >$DEMO_HOME/deployments.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    old-label: old-value
  name: deploy1
spec:
  template:
    metadata:
      labels:
        old-label: old-value
    spec:
      containers:
        - name: nginx
          image: nginx
          args:
          - one
          - two
---
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    key: value
  name: deploy2
spec:
  template:
    metadata:
      labels:
        key: value
    spec:
      containers:
        - name: busybox
          image: busybox
EOF

Declare a strategic merge patch file to inject a sidecar container:

cat <<EOF >$DEMO_HOME/patch.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: not-important
spec:
  template:
    spec:
      containers:
        - name: istio-proxy
          image: docker.io/istio/proxyv2
          args:
          - proxy
          - sidecar
EOF

Finally, define a kustomization file that specifies both a patches and resources entry:

cat <<EOF >$DEMO_HOME/kustomization.yaml
resources:
- deployments.yaml

patches:
- path: patch.yaml
  target:
    kind: Deployment
EOF

Two deployment will be patched, the expected result is:

cat <<EOF >$DEMO_HOME/out_expected.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    old-label: old-value
  name: deploy1
spec:
  template:
    metadata:
      labels:
        old-label: old-value
    spec:
      containers:
      - args:
        - proxy
        - sidecar
        image: docker.io/istio/proxyv2
        name: istio-proxy
      - args:
        - one
        - two
        image: nginx
        name: nginx
---
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    key: value
  name: deploy2
spec:
  template:
    metadata:
      labels:
        key: value
    spec:
      containers:
      - args:
        - proxy
        - sidecar
        image: docker.io/istio/proxyv2
        name: istio-proxy
      - image: busybox
        name: busybox
EOF

Run the build:

kustomize build $DEMO_HOME >$DEMO_HOME/out_actual.yaml

Confirm expectations:

diff $DEMO_HOME/out_actual.yaml $DEMO_HOME/out_expected.yaml

Let us do one more try. Redefine a kustomization file. This time only patch one deployment whose label is "key: value".

cat <<EOF >$DEMO_HOME/kustomization.yaml
resources:
- deployments.yaml

patches:
- path: patch.yaml
  target:
    kind: Deployment
    labelSelector: key=value
EOF

Run the build:

kustomize build $DEMO_HOME

Confirm expectations:

Only deploy2 is patched since its label matches "labelSelector: key=value". No change for deploy1.