Skaffold: volume structures (mountPath, persistentVolumeClaim) must be lower-case to avoid unmarshal error

Created on 14 May 2020 · 8Comments · Source: GoogleContainerTools/skaffold

Follow-up to the issue reported in the comments of this question - https://github.com/GoogleContainerTools/skaffold/issues/3883

Expected behavior

Skaffold parses the config and builds the image.

Actual behavior

Fails to parse the config

parsing skaffold config: unable to parse config: yaml: unmarshal errors:
  line 7: field mountPath not found in type v1.VolumeMount
  line 12: field persistentVolumeClaim not found in type v1.Volume

Information

Skaffold version: v1.9.0-25-gd7d0e8713-dirty
Operating system: Ubuntu 18.04.4 LTS
Contents of skaffold.yaml:

apiVersion: skaffold/v2beta3
kind: Config
build:
  artifacts:
  - image: gcr.io/k8s-skaffold/example
    kaniko:
      volumeMounts:
      - name: pvc1
        mountPath: /path
  cluster:
    volumes:
    - name: pvc1
      persistentVolumeClaim:
        claimName: kaniko-workspace

Steps to reproduce the behavior

skaffold build

I'm not a big expert in golang and learned while debugging this issue so any help would be appreciated. So far it looks like this issue with go-yaml library.

Volume-ish structs come from the k8s api and doesn't have yaml tags.
for exampe,

type VolumeMount struct {
    Name string `json:"name" protobuf:"bytes,1,opt,name=name"`
    ReadOnly bool `json:"readOnly,omitempty" protobuf:"varint,2,opt,name=readOnly"`
    MountPath string `json:"mountPath" protobuf:"bytes,3,opt,name=mountPath"`
    SubPath string `json:"subPath,omitempty" protobuf:"bytes,4,opt,name=subPath"`
    MountPropagation *MountPropagationMode `json:"mountPropagation,omitempty" protobuf:"bytes,5,opt,name=mountPropagation,casttype=MountPropagationMode"`
    SubPathExpr string `json:"subPathExpr,omitempty" protobuf:"bytes,6,opt,name=subPathExpr"`
}

whereas all skaffold structs have the yaml tag

type KanikoArtifact struct {
    AdditionalFlags []string `yaml:"flags,omitempty"`
    DockerfilePath string `yaml:"dockerfile,omitempty"`
    Target string `yaml:"target,omitempty"`
    BuildArgs map[string]*string `yaml:"buildArgs,omitempty"`
    Env []v1.EnvVar `yaml:"env,omitempty"`
    InitImage string `yaml:"initImage,omitempty"`
    Image string `yaml:"image,omitempty"`
    Cache *KanikoCache `yaml:"cache,omitempty"`
    Reproducible bool `yaml:"reproducible,omitempty"`
    SkipTLS bool `yaml:"skipTLS,omitempty"`
    VolumeMounts []v1.VolumeMount `yaml:"volumeMounts,omitempty"`
}

go-yaml ignores external structs with the json tag only and doesn't add them to the schema.

I made a quick change to verify my finding and added yaml tags in all used sctructs in vendor/k8s.io/api/core/v1/types.go, then rebuilt skaffold and reran it against the attached config. The error was gone.

Example

type VolumeMount struct {
    Name string `yaml:"name" json:"name" protobuf:"bytes,1,opt,name=name"`
    ReadOnly bool `json:"readOnly,omitempty" protobuf:"varint,2,opt,name=readOnly"`
    MountPath string `yaml:"mountPath" json:"mountPath" protobuf:"bytes,3,opt,name=mountPath"`
    SubPath string `json:"subPath,omitempty" protobuf:"bytes,4,opt,name=subPath"`
    MountPropagation *MountPropagationMode `json:"mountPropagation,omitempty" protobuf:"bytes,5,opt,name=mountPropagation,casttype=MountPropagationMode"`
    SubPathExpr string `json:"subPathExpr,omitempty" protobuf:"bytes,6,opt,name=subPathExpr"`
}

Can anyone help me verify and confirm my finding please? Also any idea on how to fix it would be appreciated.

kinbug kindocumentation prioritp3

Source

angry-cellophane

All 8 comments

There is an open PR in go-yaml to support json tags https://github.com/go-yaml/yaml/pull/564

angry-cellophane on 14 May 2020

I ran into this issue too but looking around found this other issue
https://github.com/go-yaml/yaml/issues/320#issuecomment-359259319

Basically, from the documentation, they stated:

Struct fields are only unmarshalled if they are exported (have an upper case first letter), and are unmarshalled using the field name lowercased as the default key.

so you could lowercase your fields and it should work, for example:

build:
  artifacts:
  - image: image1
    context: ./examples/app1
    kaniko:
      volumeMounts:
      - name: data
        mountpath: /data
        readonly: true

I wrote down two tests to observe this behavior that at this time I don't know if it is a bug or intended.

Failing Test:
https://travis-ci.org/github/dranes/skaffold/jobs/687835268#L325
Diff:
https://github.com/dranes/skaffold/commit/edd55c3320c1bfc98a732253a0cff6a78783105e

Passing test:
https://travis-ci.org/github/dranes/skaffold/jobs/687846445
Diff:
https://github.com/dranes/skaffold/commit/849bcbf68a596509ed438f0851ddfa9620f3c1cc

I hope this gives you some guidance or help you in some way

dranes on 17 May 2020

@dranes - Thank you for the workaround and root causing!

I believe this will be considered a documentation bug rather than a code bug, but I've added the discuss label so that we can chat about it next week.