What causes "no target shards specified for workflow %s " in vitessio/vitess?

List valid shards with `vtctl GetShardNames ` and correct the target shard specification

no target shards specified for workflow %s

Error message

no target shards specified for workflow %s

What it means

buildMaterializer requires at least one target shard in the target keyspace. After applying the ms.TargetShards filter, if the target shard list is empty, the workflow has nowhere to write and this error is returned.

Source

Thrown at go/vt/vtctl/workflow/materializer.go:546

	// that would be filtered out by the vindex anyway.
	var specifiedTargetShards []string
	switch {
	case mz.IsMultiTenantMigration():
		specifiedTargetShards = ms.WorkflowOptions.Shards
	case len(ms.SourceShards) > 0: // shard-by-shard migration
		specifiedTargetShards = ms.SourceShards
	}
	if len(specifiedTargetShards) > 0 {
		var targetShards2 []*topo.ShardInfo
		for _, shard := range targetShards {
			if slices.Contains(specifiedTargetShards, shard.ShardName()) {
				targetShards2 = append(targetShards2, shard)
			}
		}
		targetShards = targetShards2
	}
	if len(targetShards) == 0 {
		return fmt.Errorf("no target shards specified for workflow %s ", ms.Workflow)
	}

	sourceTs := mz.ts
	if ms.ExternalCluster != "" { // when the source is an external mysql cluster mounted using the Mount command
		externalTopo, err := mz.ts.OpenExternalVitessClusterServer(ctx, ms.ExternalCluster)
		if err != nil {
			return fmt.Errorf("failed to open external topo: %v", err)
		}
		sourceTs = externalTopo
	}
	differentPVs := false
	sourceVSchema, err := sourceTs.GetVSchema(ctx, ms.SourceKeyspace)
	if err != nil {
		return fmt.Errorf("failed to get source keyspace vschema: %v", err)
	}
	differentPVs = primaryVindexesDiffer(ms, sourceVSchema.Keyspace, vschema.Keyspace)

	mz.targetVSchema = targetVSchema

View on GitHub (pinned to 01a25a7d17)

Solutions

List valid shards with `vtctl GetShardNames <target-keyspace>` and correct the target shard specification
Omit the target-shards filter to use all target shards
Initialize the target keyspace with shards before creating the workflow

Example fix

// before
MoveTables --target-keyspace=copy --target-shards=xyz
// after
MoveTables --target-keyspace=copy --target-shards=0-

Defensive patterns

Strategy: validation

Validate before calling

shards, err := ts.GetShardNames(ctx, targetKeyspace)
if err != nil { return err }
if len(shards) == 0 {
    return fmt.Errorf("target keyspace %s has no shards; init them first", targetKeyspace)
}

Try / catch

if err := createWorkflow(ctx, req); err != nil {
    if strings.Contains(err.Error(), "no target shards specified") {
        // verify target keyspace shards and fix --target-shards
    }
    return err
}

Prevention

Initialize target keyspace shards and tablets before workflow creation
Validate --target-shards against GetShardNames output
Use reshard planning tools that generate valid shard ranges

When it happens

Trigger: createWorkflowStreamels or WorkflowAddTables builds a materializer where ms.TargetShards was specified but filtered to an empty set, or the target keyspace has no serving shards.

Common situations: --target-shards flag typo; target keyspace freshly created with no shards yet; shard names not matching topo convention; target keyspace name misspelled.

Related errors

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/67b426afb0269787. Report an issue: GitHub.