found duplicate container name %s in custom action. Containe

Error message

found duplicate container name %s in custom action. Container names must be unique

What it means

This validation error comes from Skaffold's schema validation pass. It fires when a `customAction` defines two or more `containers` entries with the same `name`. Custom actions require unique container names so that exec/step references can resolve unambiguously, and validateCustomActionsNames rejects duplicates during ProcessWithRunContext.

Source

Thrown at pkg/skaffold/schema/validation/validation.go:750

// - makes sure that each custom action name is unique
// - makes sure that each custom action container name is unique
func validateCustomActionsNames(runCtx *runcontext.RunContext) (errs []error) {
	acs := []latest.Action{}
	seenAcs := map[string]bool{}
	seenConts := map[string]bool{}

	for _, pipeline := range runCtx.GetPipelines() {
		acs = append(acs, pipeline.CustomActions...)
	}

	for _, a := range acs {
		if _, found := seenAcs[a.Name]; found {
			errs = append(errs, fmt.Errorf("found duplicate custom action %s. Custom action names must be unique", a.Name))
		}

		for _, c := range a.Containers {
			if _, found := seenConts[c.Name]; found {
				errs = append(errs, fmt.Errorf("found duplicate container name %s in custom action. Container names must be unique", c.Name))
			}
			seenConts[c.Name] = true
		}

		seenAcs[a.Name] = true
	}

	return
}

// validateCustomActionsLists
// - makes sure that each custom action has one or more containers
func validateCustomActionsLists(runCtx *runcontext.RunContext) (errs []error) {
	acs := []latest.Action{}

	for _, pipeline := range runCtx.GetPipelines() {
		acs = append(acs, pipeline.CustomActions...)
	}

View on GitHub (pinned to a1189de023)

Solutions

Rename one of the duplicate container entries in the customAction so every container name within a single action is unique
Check for copy-pasted container blocks in skaffold.yaml under customActions and give each a distinct name
Run `skaffold config` or re-run the command after edits to confirm validation passes

Example fix

# before
customActions:
- name: deploy-check
  containers:
  - name: runner
    image: alpine
  - name: runner
    image: busybox
# after
customActions:
- name: deploy-check
  containers:
  - name: runner
    image: alpine
  - name: verifier
    image: busybox

Defensive patterns

Strategy: validation

Validate before calling

func validateContainerNames(action CustomAction) error {
	seen := map[string]bool{}
	for _, c := range action.Containers {
		if seen[c.Name] {
			return fmt.Errorf("duplicate container name %q in custom action %q", c.Name, action.Name)
		}
		seen[c.Name] = true
	}
	return nil
}

Type guard

null

Try / catch

null

Prevention

Give each container in an action a unique, descriptive name
Review copy-pasted container blocks for unrenamed name fields
Template-generated configs: assert name uniqueness in your generator
Run schema validation locally before CI

When it happens

Trigger: Running any skaffold command that processes the config (via ProcessWithRunContext) when a customActions entry in skaffold.yaml lists two containers sharing the same name field within the same action.

Common situations: Copy-pasting a container stanza inside a customAction and forgetting to rename it; generating skaffold.yaml programmatically where names are templated incorrectly; merging config fragments that both define a container named e.g. 'build' in the same action.

Related errors

AI-assisted analysis of GoogleContainerTools/skaffold@a1189de023 (2026-09-05). Data as JSON: /api/errors/ab2d8ff4329278fa. Report an issue: GitHub.