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add inline patch document
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Liujingfang1 committed Sep 9, 2019
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[Strategic Merge Patch]: https://github.com/kubernetes/community/blob/master/contributors/devel/sig-api-machinery/strategic-merge-patch.md
[JSON Patch]: https://tools.ietf.org/html/rfc6902

# Demo: Inline Patch

A kustomization file supports patching in three ways:
- patchesStrategicMerge: A list of patch files where each file is parsed as a [Stragetic Merge Patch].
- patchesJSON6902: A list of patches and associated targetes, where each file is parsed as a [JSON Patch] and can only be applied to one target resource.
- patches: A list of patches and their associated targets. The patch can be applied to multiple objects. It auto detects whether the patch is a [Strategic Merge Patch] or [JSON Patch].

Since 3.2.0, all three support inline patch, where the patch content is put inside the kustomization file as a single string. With this feature, no separate patch files need to be created.

Make a base kustomization containing a Deployment resource.
<!-- @createKustomization @test -->
```
DEMO_HOME=$(mktemp -d)
BASE=$DEMO_HOME/base
mkdir $BASE
cat <<EOF >$BASE/kustomization.yaml
resources:
- deployments.yaml
EOF
cat <<EOF >$BASE/deployments.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: deploy
spec:
template:
metadata:
labels:
foo: bar
spec:
containers:
- name: nginx
image: nginx
args:
- one
- two
EOF
```


## Inline Patch for PatchesStrategicMerge

Create an overlay and add an inline patch in `patchesStrategicMerge` field to the kustomization file
to change the image from `nginx` to `nginx:latest`.

<!-- @addSMPatch @test -->
```
SMP_OVERLAY=$DEMO_HOME/smp
mkdir $SMP_OVERLAY
cat <<EOF >$SMP_OVERLAY/kustomization.yaml
resources:
- ../base
patchesStrategicMerge:
- |-
apiVersion: apps/v1
kind: Deployment
metadata:
name: deploy
spec:
template:
spec:
containers:
- name: nginx
image: nginx:latest
EOF
```

Running `kustomize build $SMP_OVERLAY`, in the output confirm that image is updated successfully.

<!-- @confirmSMPatch @test -->
```
test 1 == \
$(kustomize build $SMP_OVERLAY | grep "image: nginx:latest" | wc -l); \
echo $?
```

The output is
```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: deploy
spec:
template:
metadata:
labels:
foo: bar
spec:
containers:
- name: nginx
image: nginx:latest
args:
- one
- two
```
`$patch: delete` and `$patch: replace` also work in the inline patch. Change the inline patch to delete the container `nginx`.

<!-- @addDeleteSMPatch @test -->
```
cat <<EOF >$SMP_OVERLAY/kustomization.yaml
resources:
- ../base

patchesStrategicMerge:
- |-
apiVersion: apps/v1
kind: Deployment
metadata:
name: deploy
spec:
template:
spec:
containers:
- name: nginx
$patch: delete

EOF
```
Running `kustomize build $SMP_OVERLAY`, in the output confirm that the `nginx` container has been deleted.
<!-- @confirmDeleteSMPatch @test -->
```
test 0 == \
$(kustomize build $SMP_OVERLAY | grep "image: nginx" | wc -l); \
echo $?
```
The output is
```
apiVersion: apps/v1
kind: Deployment
metadata:
name: deploy
spec:
template:
metadata:
labels:
foo: bar
spec:
containers: []
```
## Inline Patch for PatchesJson6902
Create an overlay and add an inline patch in `patchesJSON6902` field to the kustomization file
to change the image from `nginx` to `nginx:latest`.
<!-- @addJSONPatch @test -->
```
JSON_OVERLAY=$DEMO_HOME/json
mkdir $JSON_OVERLAY
cat <<EOF >$JSON_OVERLAY/kustomization.yaml
resources:
- ../base

patchesJSON6902:
- target:
group: apps
version: v1
kind: Deployment
name: deploy
patch: |-
- op: replace
path: /spec/template/spec/containers/0/image
value: nginx:latest
EOF
```
Running `kustomize build $JSON_OVERLAY`, in the output confirm that image is updated successfully.
<!-- @confirmJSONPatch @test -->
```
test 1 == \
$(kustomize build $JSON_OVERLAY | grep "image: nginx:latest" | wc -l); \
echo $?
```
The output is
```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: deploy
spec:
template:
metadata:
labels:
foo: bar
spec:
containers:
- name: nginx
image: nginx:latest
args:
- one
- two
```

## Inline Patch for Patches

Create an overlay and add an inline patch in `patches` field to the kustomization file
to change the image from `nginx` to `nginx:latest`.

<!-- @addPatch @test -->
```
PATCH_OVERLAY=$DEMO_HOME/patch
mkdir $PATCH_OVERLAY
cat <<EOF > $PATCH_OVERLAY/kustomization.yaml
resources:
- ../base
patches:
- target:
kind: Deployment
name: deploy
patch: |-
apiVersion: apps/v1
kind: Deployment
metadata:
name: deploy
spec:
template:
spec:
containers:
- name: nginx
image: nginx:latest
EOF
```

Running `kustomize build $PATCH_OVERLAY`, in the output confirm that image is updated successfully.

<!-- @confirmPatch @test -->
```
test 1 == \
$(kustomize build $PATCH_OVERLAY | grep "image: nginx:latest" | wc -l); \
echo $?
```

The output is
```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: deploy
spec:
template:
metadata:
labels:
foo: bar
spec:
containers:
- name: nginx
image: nginx:latest
args:
- one
- two
```

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