How to debug Helm chart errors like "error converting YAML to JSON: yaml: mapping values are not allowed in this context"?

Question

I'm using Helm 3 and microk8s. When I try a dry run:

microk8s.helm install <...> --dry-run --debug

I see errors like

Error: YAML parse error on ./templates/deployment.yaml: error converting YAML to JSON: yaml: mapping values are not allowed in this context
helm.go:76: [debug] error converting YAML to JSON: yaml: mapping values are not allowed in this context
YAML parse error on ./templates/deployment.yaml
helm.sh/helm/v3/pkg/releaseutil.(*manifestFile).sort
    /home/circleci/helm.sh/helm/pkg/releaseutil/manifest_sorter.go:129
helm.sh/helm/v3/pkg/releaseutil.SortManifests
    /home/circleci/helm.sh/helm/pkg/releaseutil/manifest_sorter.go:98
helm.sh/helm/v3/pkg/action.(*Configuration).renderResources
    /home/circleci/helm.sh/helm/pkg/action/install.go:455
helm.sh/helm/v3/pkg/action.(*Install).Run
    /home/circleci/helm.sh/helm/pkg/action/install.go:214
main.runInstall
...

I found several questions with a similar error, but the answer is usually just asking for read a chart code. I have a large chart and need to debug this error on my own. And guessing which line it complains about doesn't seem meaningful.

Is there a way to know what exactly is wrong in the config?

Answer 1

Try: helm template ... --debug > foo.yaml

This'll output the rendered chart to foo.yaml (and the helm error stacktrace to stderr). Then find the template filename in question from the helm error and look through the rendered chart for a line like # Source: the-template-name.yaml. YAML to JSON conversion is done separately for each YAML object, so you may have multiple instances of the same # Source: the-template-name.yaml.

Look n lines below each # Source: ... comment for an error, where n is the line number of the error reported by Helm render.