Proper kustomize syntax to replace the value of list element with condition

[kastl-ars]

Given this YAML file, what would be the proper syntax to patch the value of the env element that has TRACING_COLLECTOR_HOST as name?

This works, but hardcodes "use the second element in the list" (.../env/1/...):

- op: replace
  path: /spec/template/spec/containers/0/env/1/value
  value: newvalue

I find no syntax that kustomize accepts, that lets me define this. Is this possible?

The RFCs for JSON patches contain only very basic paths, unfortunately.

yq accepts something like this:

.spec.template.spec.containers.0.env[] | select(.name == "TRACING_COLLECTOR_HOST").value

Here are some of the things I tried with kustomize:

  path: /spec/template/spec/containers/0/env/(.name == 'TRACING_COLLECTOR_HOST')/value
  path: /spec/template/spec/containers/0/env[](.name == 'TRACING_COLLECTOR_HOST')/value
  path: /spec/template/spec/containers/0/env/(.name == 'TRACING_COLLECTOR_HOST')/value
  path: /spec/template/spec/containers/0/env/(name == 'TRACING_COLLECTOR_HOST')/value
  path: /spec/template/spec/containers/0/env/(/name == 'TRACING_COLLECTOR_HOST')/value
  path: /spec/template/spec/containers/0/env/name == 'TRACING_COLLECTOR_HOST'/value
...

[ChristianCiach]

This is simply not possible with patchesJson6902.

What is commonly done instead is to use the test operation to make sure that you are actually patching the expected element. Something like that:

- op: test
  path: /spec/template/spec/containers/0/env/1/name
  value: TRACING_COLLECTOR_HOST
- op: replace
  path: /spec/template/spec/containers/0/env/1/value
  value: newvalue

You should probably also add a test for /spec/template/spec/containers/0/name to make sure that you are patching the expected container.

[ChristianCiach]

If/when #5630 gets merged, you could probably use the replacement feature to patch this element, because the replacement feature supports a mightier syntax for selecting the target element.