Update a local package

Update a customized local package with upstream (remote) package changes.

Packages can be arbitrarily customized and later merge updates from upstream.

Topics

kpt pkg update

Because kpt package contents are resource configuration (data) rather than templates or DSLs (code), it is possible to merge different versions of the package together using the structure of the resources to compute differences.

This allows package consumers to customize their copy, and merge updates from upstream.

The technique of merging fields to perform updates is also how kubectl apply updates remote cluster resources with local file changes, without overwriting changes to the resources made by the cluster control-plane (e.g. an autoscaler can set replicas without apply overwriting them).

See [update strategies] for more choices on how to merge upstream changes.

kpt pkg update explained

Following is a short explanation of the command that will be demonstrated in this guide.

  • Copy the staging/cockroachdb subdirectory out of the [kubernetes examples] git repo
  • Edit the local package contents
  • Commit the changes
  • Update the local package with upstream changes from a new version

Steps

Fetch a remote package

Packages can be fetched at specific versions defined by git tags, and have updated to later versions to merge in upstream changes.

Fetch Command

export REPO=https://github.com/GoogleContainerTools/kpt.git
kpt pkg get $REPO/package-examples/helloworld-set@v0.3.0 helloworld

Fetch the helloworld-set package at version v0.3.0.

Fetch Output

fetching package /package-examples/helloworld-set from https://github.com/GoogleContainerTools/kpt to helloworld

Each subdirectory within a git repo may be tagged with its own version using the subdirectory path as a tag prefix, and kpt will automatically resolve the subdirectory version.

package-examples/helloworld-set@v0.3.0 is resolved to the tag package-examples/helloworld-set/v0.3.0 if it exists, otherwise it is resolved to the tag v0.3.0.

Edit the contents

Edit the contents of the package by making changes to it.

Old local configuration

# helloworld/deploy.yaml (upstream)
...
        image: gcr.io/kpt-dev/helloworld-gke:v0.1.0 # {"$ref":"#/definitions/io.k8s.cli.substitutions.image-tag"}
...
        env:
        - name: PORT
          value: "80" # {"$ref":"#/definitions/io.k8s.cli.setters.http-port"}
...

The old package contents without local modifications.

vi helloworld/deploy.yaml

New local configuration

# helloworld/deploy.yaml (locally modified)
...
        image: gcr.io/kpt-dev/helloworld-gke:v0.1.0 # {"$ref":"#/definitions/io.k8s.cli.substitutions.image-tag"}
...
        env:
        - name: PORT
          value: "80" # {"$ref":"#/definitions/io.k8s.cli.setters.http-port"}
        - name: NEW_ENV # This is a local package addition
          value: "local package edits"
...

The new package contents with local modifications.

Commit local changes

In order for updates to be easily undone, configuration must be committed to git prior to performing a package update.

kpt will throw an error if trying to update a package and the git repo has uncommitted changes.

git init
git add .
git commit -m "add helloworld package at v0.3.0"

Merge upstream changes

Package updates are performed by fetching the upstream package at the specified version and applying the upstream changes to the local package.

Merge Command

kpt pkg update helloworld@v0.5.0 --strategy=resource-merge

Update the local package to the upstream version v0.5.0 by doing a 3-way merge between 1) the original upstream commit, 2) the local (customized) package, 3) the new upstream reference.

Merge Output

updating package helloworld to v0.5.0

Merge Changes

--- a/helloworld/deploy.yaml
+++ b/helloworld/deploy.yaml
@@ -31,7 +31,7 @@ spec:
     spec:
       containers:
       - name: helloworld-gke
-        image: gcr.io/kpt-dev/helloworld-gke:0.1.0 # {"$ref":"#/definitions/io.k8s.cli.substitutions.image-tag"}
+        image: gcr.io/kpt-dev/helloworld-gke:v0.3.0 # {"$ref":"#/definitions/io.k8s.cli.substitutions.image-tag"}
         ports:
         - name: http
           containerPort: 80 # {"$ref":"#/definitions/io.k8s.cli.setters.http-port"}
diff --git a/helloworld/service.yaml b/helloworld/service.yaml
index 0853ee1..c938fde 100644
--- a/helloworld/service.yaml
+++ b/helloworld/service.yaml
@@ -22,7 +22,7 @@ metadata:
   labels:

The Deployment was updated with a new image tag.

--- a/helloworld/service.yaml
+++ b/helloworld/service.yaml
@@ -22,7 +22,7 @@ metadata:
   labels:
     app: hello
 spec:
-  type: LoadBalancer
+  type: NodePort
   selector:
     app: hello
   ports:

The Service was updated with a new type.

--- a/helloworld/Kptfile
+++ b/helloworld/Kptfile
@@ -5,10 +5,10 @@ metadata:
 upstream:
     type: git
     git:
-        commit: 3d721bafd701deb06aeb43c5ea5afda3134cfdd6
+        commit: 3f173ad974081896b47f6929b2c3cb595d71af94
         repo: https://github.com/GoogleContainerTools/kpt
         directory: /package-examples/helloworld-set
-        ref: v0.3.0
+        ref: v0.5.0
 openAPI:
     definitions:
         io.k8s.cli.setters.http-port:

The Kptfile was updated with the new upstream metadata.

View new package contents

# helloworld/deploy.yaml (updated from upstream)
...
        image: gcr.io/kpt-dev/helloworld-gke:v0.3.0 # {"$ref":"#/definitions/io.k8s.cli.substitutions.image-tag"}
...
        env:
        - name: PORT
          value: "80" # {"$ref":"#/definitions/io.k8s.cli.setters.http-port"}
        - name: NEW_ENV # This is a local package addition
          value: "local package edits"
...

The updated local package contains both the upstream changes (new image tag), and local modifications (additional environment variable).

Last modified July 7, 2020: Docs: Fix W3 Link Checker results (c78d6c56)