Templating similar to kustomize but with multiple overlays

This requires yq and yaml-patch

docker build --tag kastemais .

XXX

An application describes the minimum to deploy a service

An overlay contains YAML patches that modify an application with a specific purpose, e.g.

• Adding namespace
• Adding labels and annotations
• Adding resources
• Adding sidecars

Stored in a subdirectory of /app, e.g. /app/nginx

Contains one or more YAML documents in one or more files - multiple documents per file a allowed

All files must have a leading document separator ---

Stored in a subdirectory if /overlay, e.g. /overlay/sidecar-monitoring

Overlays can be applied to all documents

Overlays can be applied to specific documents using filters

cat app/nginx/deployment.yaml | docker run -i kastemais yq r - metadata.name

cat app/nginx/deployment.yaml | docker run -i kastemais yaml-patch -o overlay/ci-annotations/patch-all.yaml

This also works for multiple documents:

cat app/nginx/*.yaml | docker run -i kastemais yaml-patch -o overlay/ci-annotations/patch-all.yaml

NAME=$(./yq r app/nginx/deployment.yaml metadata.name)
cat app/nginx/deployment.yaml | docker run -i kastemais yq w - metadata.name ${NAME}-qa

TODO: How to filter?

Merge into one YAML document in the form (see merge_documents() in functions.sh):

apiVersion: v1
kind: List
items:
- ...
- ...

This is also valid:

apiVersion: v1
kind: List
items:
-
  ...
-
  ...

yq can only operate on numerically indexed documents in a file:

$ cat app/nginx/*.yaml | yq3 -d'*' r - kind
ConfigMap
Deployment
Service

yq can also merge multiple documents within a file when in the correct order (see merge_documents() in functions.sh)

Workaround: Split documents into separate files

$ cat app/nginx/*.yaml | csplit --prefix=document- --suffix-format=%02d.yaml --elide-empty-files --quiet - /---/ '{*}'
$ ls -l document-*.yaml
document-00.yaml  document-01.yaml  document-02.yaml

TODO: Description which application from /app and which overlays from /overlay to apply.

TODO: Is this in scope? If so...

• Support substitution from environment variables
• Explicit list of variables to substitute
• Support .env file?

Workaround: envsubst