kpatch

kpatch is a tool to manipulate Kubernetes manifests. It is designed to be used in build pipelines in a manner similar to standard unix tools.

kpatch was born out of a frustration with helm manifests needing tweaking and kustomizer having good manipulation capabilities but being locked behind a strange interface.

It is based around three very simple features; selectors, actions and merges.

WIP 💥

kpatch is still in early development but has been released early as it does most of what I'd intended it to. There are definitely edge cases that will cause a panic. I do not anticipate the expression language nor command line usage to change in incompatible ways but given the early days reserve the right. Code structure will definitely change.

Selectors

Selectors use gval to match manifests to process. If a manifest does not match the selector it is printed as it was read. Some example selectors:

• kind == "Deployment" && metadata.name == "my-nginx"
• metadata.label.app == "my-app"
• metadata.name =~ "^stdio"

Actions

Action expressions are manipulations that will be applied to resources. Manifests can be dropped, merged and modified. Some example expressions:

• drop() - Excludes the manifest from output
• metadata.name = metadata.name + "-my-suffix" - Appends -my-suffix to metadata.name field.
• metadata.labels = merge(metadata.labels, yaml("{ timestamp: 123456789 }"))

Merges

Merges are simple data merges of the manifest with another yaml file. Merges apply only at the root level. To merge a field use the merge function in an expression.

Examples

For a more detailed set of examples, see examples

Append a suffix to service names

kpatch -s 'kind == "Service"' -a 'metadata.name = metadata.name + "-service"' myyaml.yaml

Delete a document

kpatch -s 'metadata.name == "deleteme"' -a 'drop' myyaml.yaml

Merge common metadata in to namespace

cat myyaml.yaml | kpatch -s 'kind == "Namespace"' -m common-metadata.yaml

Apply multiple actions (to all documents)

kpatch -a 'name = "test"' -a 'name = name + "-test"' -a 'foo = "bar"' myyaml.yaml

Chain usage

cat myyaml.yaml | kpatch -s 'kind == "rule"' -a 'drop' | kpatch -a 'name = name + "-test"'`