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Overlays and patches

Introduction

Patches are partial configuration blocks that can be overlaid onto a given package.

You can store them and ship them with a package to provide a quick way to modify settings and generate different packages from a given base package, overlaying patches on top until you get your desired state.

Patches work by utilizing the Package object model and manipulating it using kustomize.

The name parameter of the object being overlaid (for example: a database or table) is used as a key and array types will be merged according to the strategic merge mechanism.

There is no mechanism to patch code files currently, only configuration files i.e. databases and pipelines.

Using patches

Adding a pipeline

  1. To create a patch, use the add command and specify patch as your new object:

    kxi package -q init mypkg --force
    kxi package -q add --to mypkg patch --name my-first-patch
    cat mypkg/patches/my-first-patch.yaml
    
    uuid: f184d492-e076-4043-87d1-be73053030da
    kind: Package
    apiVersion: pakx/v1
    metadata:
      name: target
    spec:
      uuid: 632f16cd-def8-48af-88b9-7f6f2e828064
      manifest: {}
      tables:
        uuid: 88f0c110-169f-4ce6-b97c-60a28312ab31
        schemas: []
      databases: []
      pipelines: []
      router: null
      views: []
      deployment_config: null
      data_files: {}
    

    This adds a patch file to the patches directory. The new file includes the structure required for a patch file, but no pipeline.

    Be careful when you modify the patch file

    • Do not modify the headers above the spec: field
    • It is good practice to remove everything inside spec: except what you want to patch
  2. You can see the patch object is now present in the manifest file:

    kxi package info mypkg
    
    ==PATH==
    /builds/kxdev/documentation/insights/mypkg
    
    ==OBJECT==
    Package
    
    ==Manifest==
    uuid: bec63ed1-6063-48e3-a147-633b746d2f61
    name: mypkg
    version: 0.0.1
    metadata:
      description: ''
      authors:
      - {}
    entrypoints:
      default: init.q
    patches:
    - uuid: bdbcfd20-b795-4ff6-ae66-5b688e087daa
      name: my-first-patch
    

  3. Modify the patch to add a new pipeline:

    patchspec=$(cat mypkg/patches/my-first-patch.yaml | grep spec: -B10 | cat - <(echo "  pipelines: [{name: mynewpipeline, spec: init.q}]"))
    echo "$patchspec" > mypkg/patches/my-first-patch.yaml
    cat mypkg/patches/my-first-patch.yaml
    
    uuid: f184d492-e076-4043-87d1-be73053030da
    kind: Package
    apiVersion: pakx/v1
    metadata:
      name: target
    spec:
      pipelines: [{name: mynewpipeline, spec: init.q}]
    

  4. Apply or "overlay" this patch onto your current package using the overlay command:

    Without specifying any other information, the overlay command resolves All the patches found in the manifest:

    kxi package overlay mypkg
    kxi package info mypkg | grep pipelines: -A5
    
    Found patch to overlay: mypkg/patches/my-first-patch.yaml
    Writing /builds/kxdev/documentation/insights/mypkg/manifest.yaml
    pipelines:
      mynewpipeline:
        file: pipelines/mynewpipeline.yaml
    router: ''
    views: {}
    deployment_config: ''
    

    When you specify patches after the package name, you can select any valid patch file, they dont even need to be located inside a package.

    kxi package overlay mypkg mypkg/patches/my-first-patch.yaml
    kxi package info mypkg | grep pipelines: -A5
    
    Writing /builds/kxdev/documentation/insights/mypkg/manifest.yaml
    pipelines:
      mynewpipeline:
        file: pipelines/mynewpipeline.yaml
    router: ''
    views: {}
    deployment_config: ''
    

Modifying tables

To modify a table, you must patch the Database because tables are contained inside the Database construct :

kxi package -q init mypkg --force
kxi package -q add --to mypkg database --name mydb 
# This automatically populates a "default" table

kxi package -q add --to mypkg patch --name my-db-patch

read -r -d '' dbspec <<'EOF'
    databases:
      - name: mydb
        tables:
          schemas: 
            - name: default
              description: We've changed the default table's description too!
              type: basic 
              columns:
                - name: myfloat
                  type: float
                  description: we've added a new float column called myfloat 
                - name: x2 
                  type: symbol
                  description: The default x2 column has changed type
EOF

# The patch might look a little complex, but it's just a few nested structs 
# N.B We have indented it here to nest it under the `spec` field

patchspec=$(cat mypkg/patches/my-db-patch.yaml | grep spec: -B10 | cat - <(echo "  $dbspec"))
echo "$patchspec" > mypkg/patches/my-db-patch.yaml
# This is just to stitch the header with the dbspec we wrote

cat mypkg/patches/my-db-patch.yaml
kxi package overlay mypkg

echo""
echo "----Resultant schema for 'default' table----"
echo "--------------------------------------------"
cat mypkg/databases/mydb/tables/default.yaml
uuid: e2b92c6c-a118-4de9-941d-2e18b2067e50
kind: Package
apiVersion: pakx/v1
metadata:
  name: target
spec:
  databases:
      - name: mydb
        tables:
          schemas: 
            - name: default
              description: We've changed the default table's description too!
              type: basic 
              columns:
                - name: myfloat
                  type: float
                  description: we've added a new float column called myfloat 
                - name: x2 
                  type: symbol
                  description: The default x2 column has changed type
Found patch to overlay: mypkg/patches/my-db-patch.yaml
Writing /builds/kxdev/documentation/insights/mypkg/manifest.yaml

----Resultant schema for 'default' table----
--------------------------------------------
uuid: b590e0b8-34d8-4c75-b80c-c0a5a5af5840
columns:
- description: we've added a new float column called myfloat
  name: myfloat
  type: float
- description: The default x2 column has changed type
  name: x2
  type: symbol
description: We've changed the default table's description too!
name: default
type: basic

Column ordering

After patching you can observe the columns have changed order. The new column has been added in at the top. If your application requires specific column ordering, then you need to do this manually.

Referencing dependency patches

You can also reference patches held in other packages to minimize the need to copy patch specs that you use regularly.

Referenced dependencies must already be installed.

Referencing a patch from a dependency can only be done after that dependency is installed.

In the below example you explicitly run: kxi package install myotherdep. This allows the kxi package to resolve it properly when you then call overlay.

You do this in the following way:

kxi package -q init myotherpkg --force
# setup

kxi package -q add --to myotherpkg patch --name patch-from-afar
patchspec=$(cat myotherpkg/patches/patch-from-afar.yaml | grep spec: -B10 | cat - <(echo "  pipelines: [{name: mynewpipeline, spec: init.q}]"))
echo "$patchspec" > myotherpkg/patches/patch-from-afar.yaml
# add a patch to myother pkg

_=$(kxi package -q install myotherpkg)
# install myotherpkg so that you can reference it 

kxi package -q add --to mypkg dep --name myotherpkg --version 0.0.1 
# add a dependency on myotherpkg to mypkg

kxi package -q add --to mypkg patch --name patch-from-afar --dep myotherpkg
# add a patch in mypkg referencing a patch in myotherpkg

kxi package -q overlay mypkg

# see that you have successfully used the patch adding a new pipeline from myotherpkg
kxi package info mypkg | grep pipelines: -A5
pipelines:
  mynewpipeline:
    file: pipelines/mynewpipeline.yaml
router: ''
views: {}
deployment_config: ''