What causes "unsupported relabel action: %v" in thanos-io/thanos?

Remove or replace the offending rule's action with one in the supported set for that call site.

unsupported relabel action

Error message

unsupported relabel action: %v

What it means

ParseRelabelConfig optionally restricts relabel actions: when supportedActions is non-nil, any rule whose cfg.Action is not in that set causes errors.Errorf("unsupported relabel action: %v"). Callers use it to whitelist only the actions meaningful for a given subsystem (e.g. bucket verification only allows a subset).

Solutions

Remove or replace the offending rule's action with one in the supported set for that call site.
Check the supportedActions map at the call site (e.g. pkg/block/fetcher.go usages like ParsedActions for bucket verification) to see which actions are allowed.
Fix typos/casing — actions are lowercase enum values (keep, drop, replace, keep, labeldrop, labelmap, hashmod, uppercase, lowercase).
Upgrade Thanos if the action is a newer Prometheus relabel action not yet in the allow-list.

Example fix

// before
// - action: labelmap
//   regex: probe_(.*)
// after (if only keep/drop supported)
// - action: keep
//   source_labels: [probe]
//   regex: "true"

Defensive patterns

Strategy: validation

Validate before calling

// Go: check actions against the allow-list before calling ParseRelabelConfig
for _, c := range cfgs {
    if _, ok := supportedActions[c.Action]; !ok {
        return fmt.Errorf("action %q not allowed here", c.Action)
    }
}

Try / catch

cfgs, err := block.ParseRelabelConfig(contentYaml, supportedActions)
if err != nil && strings.Contains(err.Error(), "unsupported relabel action") {
    return fmt.Errorf("check allowed actions for this subsystem: %w", err)
}

Prevention

Know which actions the call site whitelists and keep dedicated config files per subsystem.
Use exact lowercase action names (keep, drop, replace, labelmap, labeldrop, hashmod, uppercase, lowercase).
Do not copy scrape-config relabel rules verbatim into bucket/tool configs.
Verify action support against the Thanos/Prometheus version you deploy.

When it happens

Trigger: Calling ParseRelabelConfig with supportedActions set (e.g. via APIs that accept only specific actions) while the YAML file contains a rule with an action outside that set — such as 'labelmap', 'hashmod', or 'lowercase' where only keep/drop/replace are allowed.

Common situations: Reusing a general-purpose relabel file (from Prometheus scrape config) in a Thanos context that whitelists actions; typos in action names ('kept', 'Drop' with wrong case); using newer Prometheus actions on an older Thanos build that doesn't know them.

Related errors

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/5ed42d6e4b516898. Report an issue: GitHub.

Appendix: source

Thrown at pkg/block/fetcher.go:1413

)

// ParseRelabelConfig parses relabel configuration.
// If supportedActions not specified, all relabel actions are valid.
func ParseRelabelConfig(contentYaml []byte, supportedActions map[relabel.Action]struct{}) ([]*relabel.Config, error) {
	var relabelConfig []*relabel.Config
	if err := yaml.Unmarshal(contentYaml, &relabelConfig); err != nil {
		return nil, errors.Wrap(err, "parsing relabel configuration")
	}
	for _, cfg := range relabelConfig {
		if err := cfg.Validate(prommodel.UTF8Validation); err != nil {
			return nil, errors.Wrap(err, "validate relabel config")
		}
	}

	if supportedActions != nil {
		for _, cfg := range relabelConfig {
			if _, ok := supportedActions[cfg.Action]; !ok {
				return nil, errors.Errorf("unsupported relabel action: %v", cfg.Action)
			}
		}
	}

	return relabelConfig, nil
}

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