googleapis/mcp-toolbox · error

unable to create session: %v

Error message

unable to create session: %v

What it means

This error wraps any failure that occurs while creating the Cassandra session during source initialization in the MCP Toolbox. Config.Initialize calls initCassandraSession, and if the cluster cannot be contacted or configured incorrectly, the underlying gocql error is wrapped with this message.

Source

Thrown at internal/sources/cassandra/cassandra.go:62

type Config struct {
	Name                   string   `yaml:"name" validate:"required"`
	Type                   string   `yaml:"type" validate:"required"`
	Hosts                  []string `yaml:"hosts" validate:"required"`
	Keyspace               string   `yaml:"keyspace"`
	ProtoVersion           int      `yaml:"protoVersion"`
	Username               string   `yaml:"username"`
	Password               string   `yaml:"password"`
	CAPath                 string   `yaml:"caPath"`
	CertPath               string   `yaml:"certPath"`
	KeyPath                string   `yaml:"keyPath"`
	EnableHostVerification bool     `yaml:"enableHostVerification"`
}

// Initialize implements sources.SourceConfig.
func (c Config) Initialize(ctx context.Context, tracer trace.Tracer) (sources.Source, error) {
	session, err := initCassandraSession(ctx, tracer, c)
	if err != nil {
		return nil, fmt.Errorf("unable to create session: %v", err)
	}
	s := &Source{
		Config:  c,
		Session: session,
	}
	return s, nil
}

// SourceConfigType implements sources.SourceConfig.
func (c Config) SourceConfigType() string {
	return SourceType
}

var _ sources.SourceConfig = Config{}

type Source struct {
	Config
	Session *gocql.Session

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Check that the Cassandra cluster is reachable from the toolbox host (hosts list, port 9042, firewall).
2. Verify username/password are both set together and correct.
3. Confirm ProtoVersion matches your Cassandra/ScyllaDB server version.
4. Verify the keyspace exists; omit it if you don't need one.
5. Inspect the wrapped inner error (%v) for the root cause.

Example fix

// before
c := cassandra.Config{Hosts: []string{"wrong-host"}}
// after
c := cassandra.Config{Hosts: []string{"127.0.0.1"}, Username: "cassandra", Password: "cassandra", Keyspace: "myks"}

if len(cfg.Hosts) == 0 { return errors.New("cassandra hosts required") }
if cfg.Password != "" && cfg.Username == "" { return errors.New("password requires username") }

src, err := cfg.Initialize(ctx, tracer)
if err != nil {
    var netErr net.Error
    if errors.As(err, &netErr) { /* handle connectivity */ }
    return fmt.Errorf("cassandra init failed: %w", err)
}

When it happens

Trigger: Calling Initialize on a cassandra.Config when initCassandraSession fails: invalid auth config, unreachable hosts, bad protocol version, or keyspace issues.

Common situations: Cassandra cluster down or wrong host/port, wrong ProtoVersion for the server, keyspace that does not exist, network/firewall blocking the CQL port 9042.

Related errors

• failed to create Cassandra session: %w
• unable to create db connection: %w
• unable to initialize source %q: %w
• error initializing Valkey client: %s
• failed to initialize resources: %w

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/51efb76cc9065ab8. Report an issue: GitHub.