pulumi/pulumi · error

failed to serialize configuration: %w

Error message

failed to serialize configuration: %w

What it means

The Pulumi NodeJS language host failed to JSON-serialize the stack configuration before launching the user's program process (constructConfig in main.go:1120). The error is wrapped with this message and returned to the engine inside RunResponse.Error instead of the program being run. This almost always means a config key in the RunRequest could not be parsed by config.ParseKey, i.e. it is malformed.

Source

Thrown at sdk/nodejs/cmd/pulumi-language-nodejs/main.go:903

			if err != nil {
				return &pulumirpc.RunResponse{Error: err.Error()}, nil
			}
		case response := <-responseChannel:
			return response, nil
		}
	}
}

// Launch the runtime process and wait for it to complete.  Report success or any errors using the
// `responseChannel` arg.
func (host *nodeLanguageHost) execRuntime(ctx context.Context, req *pulumirpc.RunRequest,
	engineClient pulumirpc.EngineClient, runtimeBin, runPath, address, pipesDirectory string,
) *pulumirpc.RunResponse {
	// Actually launch nodejs or bun and process the result of it into an appropriate response object.
	args := host.constructArguments(req, runPath, address, pipesDirectory)
	config, err := host.constructConfig(req)
	if err != nil {
		err = fmt.Errorf("failed to serialize configuration: %w", err)
		return &pulumirpc.RunResponse{Error: err.Error()}
	}
	configSecretKeys, err := host.constructConfigSecretKeys(req)
	if err != nil {
		err = fmt.Errorf("failed to serialize configuration secret keys: %w", err)
		return &pulumirpc.RunResponse{Error: err.Error()}
	}

	env := os.Environ()
	env = append(env, pulumiConfigVar+"="+config)
	env = append(env, pulumiConfigSecretKeysVar+"="+configSecretKeys)

	opts, err := parseOptions(req.Info.Options.AsMap(), host.runtime)
	if err != nil {
		return &pulumirpc.RunResponse{Error: err.Error()}
	}

	if opts.typescript {

View on GitHub (pinned to 793f7b2e16)

Solutions

1. Find the offending key in the error detail and fix it with `pulumi config set <project>:<name> <value>` using a valid '<package>:<name>' key format.
2. Run `pulumi config` to list all keys for the stack and remove/rename malformed entries with `pulumi config rm`.
3. Ensure all pulumi CLI and @pulumi/pulumi SDK versions are current, since config key format transition bugs were fixed over time.
4. If using automation API, validate config key strings before passing them to LocalWorkspace program runs.

Example fix

// before: malformed key set directly
pulumi config set mykey value

// after: fully-qualified key
pulumi config set myproject:mykey value

// Validate config keys before running pulumi
for key in $(pulumi config --show-secrets --json | jq -r 'keys[]'); do
  if ! echo "$key" | grep -qE '^[^:]+:[^:]+'; then
    echo "Malformed config key: $key"; exit 1
  fi
done

When it happens

Trigger: LanguageRuntime.Run RPC is invoked with req.Config containing a key that fails config.ParseKey (does not look like '<namespace>:<name>' with a valid namespace/name), or json.Marshal of the transformed config map fails. The failing call is host.constructConfig(req) at sdk/nodejs/cmd/pulumi-language-nodejs/main.go:901.

Common situations: Config entries written with malformed keys (e.g. 'foo' without a project/package prefix, empty names, or invalid characters) such as when setting config manually or via automation API; mismatches between old (<pkg>:config:<name>) and new config key formats; corrupted stack state config bags.

Related errors

• failed to serialize configuration secret keys: %w
• could not marshal stack configuration: %w
• unsupported runtime: %s
• could not start health check host RPC server: %w
• could not start language host RPC server: %w

AI-assisted analysis of pulumi/pulumi@793f7b2e16 (2026-08-31). Data as JSON: /api/errors/4bfd4a38fa474485. Report an issue: GitHub.