feat(spanner): Enable EEF for cloud spanner when direct access is enabled

[kinsaurralde]

No description provided.

[gemini-code-assist]

Code Review

This pull request updates the Spanner client to enable GCP fallback by default and configures a fallback period of three minutes. Feedback was provided to improve the robustness of environment variable parsing, ensuring that invalid or malformed values do not accidentally disable the fallback feature.

[gemini-code-assist]

The current implementation of environment variable parsing for GOOGLE_SPANNER_ENABLE_GCP_FALLBACK will set isFallbackEnabled to false if the environment variable is set to an invalid boolean string (e.g., a typo). Since the intended default behavior is true when the variable is unset, it is more robust to preserve that default if a malformed value is provided. This ensures that the feature remains enabled unless explicitly disabled with a valid 'false' value, adhering to the principle of not altering defaults of existing stable code paths.

isFallbackEnabled := true
if val, ok := os.LookupEnv("GOOGLE_SPANNER_ENABLE_GCP_FALLBACK"); ok {
	if b, err := strconv.ParseBool(val); err == nil {
		isFallbackEnabled = b
	}
}

References

1. When introducing new components with different default behaviors, avoid altering the defaults of existing, stable code paths to prevent breaking changes for backward compatibility.

[rahul2393]

Is there any issue/discussion for deciding 3 minute specifically?