Upgrading your database client libraries can bring performance improvements, bug fixes, and better compatibility with cloud environments—but sometimes, they break things in unexpected ways. A common hiccup developers face after upgrading the MySQL client for use with Google Cloud SQL is a connection failure accompanied by the cryptic error: ER_NOT_SUPPORTED_AUTH_MODE. This issue stems from changes in authentication plugin support and how user credentials are managed in MySQL. Let’s untangle what causes this problem, how to fix it, and what lessons can be learned from it.
TL;DR
Upgrading a MySQL client to a newer version can provoke a connection error (ER_NOT_SUPPORTED_AUTH_MODE) when trying to connect to Google Cloud SQL. This occurs because the new client no longer supports the old mysql_native_password plugin used by default in some older Cloud SQL user accounts. The fix involves migrating affected users to the caching_sha2_password authentication plugin. This article walks you through the why and the how, offering insight to prevent future similar mishaps.
Understanding the Error: ER_NOT_SUPPORTED_AUTH_MODE
The error message ER_NOT_SUPPORTED_AUTH_MODE translates to “Client does not support authentication protocol requested by server; consider upgrading MySQL client.” The irony, of course, is that the client has just been upgraded—which causes it to reject the login method used by the user account you’re trying to connect with.
The root cause lies in authentication plugin compatibility between the MySQL client and server. Upgraded clients, particularly those post-MySQL 8.0, drop support for older and less secure auth mechanisms, particularly mysql_native_password in favor of caching_sha2_password. When the Cloud SQL user is still configured to use the outdated plugin, the connection fails.
Why This Happens with Google Cloud SQL
Google Cloud SQL, being a managed service, limits direct control over server configurations for security and stability. While this simplifies many operations, it introduces complexity when client behavior changes—as in the case of authentication plugins. Older Cloud SQL users may have been created when mysql_native_password was the default. Unless explicitly updated, these user configurations remain unchanged.
When a client that no longer supports mysql_native_password attempts a connection, it negotiates with the server expecting a modern auth workflow. Instead, it receives an outdated method and gracefully refuses, resulting in the error.
Key Symptoms and Clues
- Error occurs immediately after upgrading the database client library on your application or local environment
- Cloud SQL instance is accessible, but authentication fails with ER_NOT_SUPPORTED_AUTH_MODE
- Error message clearly indicates an unsupported authentication plugin
- Other users or instances that haven’t been upgraded continue to work fine
These clues tell us the problem isn’t with the Cloud SQL instance, but rather with account configuration and how it interacts with the newer client. This makes solving it relatively straightforward—once you’re aware of the underlying mechanics.
Authentication Plugins in MySQL: A Quick Overview
MySQL supports multiple authentication plugins, each offering varying levels of security and performance. Understanding what each plugin does helps clarify why the newer clients behave differently. Here are the two key players relevant to this error:
- mysql_native_password: Once the default, this plugin hashes user passwords using older algorithms. Compatible with many older clients but now considered less secure.
- caching_sha2_password: The more secure and modern plugin, adopted as default starting with MySQL 8.0. Offers better password security and faster reauthentication for clients that support it.
Developers upgrading from MySQL 5.6/5.7 clients to 8.0+ might face this friction point, as the client silently refuses to use an outdated plugin.
Resolving the Issue: Migrating the Auth Plugin
The most effective solution is to switch your user account in Cloud SQL to use the supported and secure caching_sha2_password plugin. Follow this simple process to enable compatibility with your upgraded clients:
- Connect to your Cloud SQL instance using an existing compatible client (if necessary, downgrade temporarily)
- Run the following SQL command to update the plugin:
ALTER USER 'your_user'@'%' IDENTIFIED WITH 'caching_sha2_password' BY 'your_secure_password';
- Flush privileges to ensure the changes take effect immediately:
FLUSH PRIVILEGES;
This change tells MySQL to store and verify passwords using the newer authentication method. Your upgraded MySQL client should now connect successfully without any issues.
Alternative Workarounds (Not Recommended)
While updating the authentication plugin is the most robust and forward-proof approach, developers sometimes fall back on quicker, riskier fixes. These include:
- Downgrading the MySQL client – Retains compatibility with the existing server setup but reintroduces old security vulnerabilities.
- Creating a new user with the updated plugin – May work as a short-term measure but leaves legacy users behind and unmanaged.
- Modifying client connection libraries to force plugin usage – Hacky and undocumented; easily breaks with future updates.
It’s better to do the hard work of updating the plugin than to rely on these future headaches. Security, especially in the cloud, should be a first-class citizen in every update.
Best Practices Going Forward
Avoiding this kind of snag in the future requires a bit of planning and vigilance. Here are a few recommendations:
- Audit Authentication Plugins: Periodically review users in your Cloud SQL instances to ensure they’re using modern, supported plugins.
- Establish a Staging Environment: Test client upgrades in an environment that simulates production as closely as possible.
- Follow GCP Release Notes: Changes to default behaviors, like authentication mechanisms, are typically documented in GCP’s release notes—subscribe to them.
- Automate Plugin Enforcement: If your organization uses infrastructure-as-code, enforce plugin policies for all new users and connections.
A Broader Lesson in Cloud Interoperability
This incident is more than just a point error in an upgrade cycle—it reflects the challenge of keeping backend systems secure and up-to-date while ensuring compatibility with a rapidly evolving software ecosystem. Google Cloud SQL insulates users from server patching and updates, but authentication and access remain shared responsibilities.
For developers and DevOps teams, this underscores the importance of understanding the layers of abstraction provided by cloud providers. Some components are hands-off—and others, like user configurations, require ongoing care.
Conclusion
The ER_NOT_SUPPORTED_AUTH_MODE error encountered after upgrading a MySQL client isn’t a bug—it’s a feature that points to modernization in database authentication. While initially confusing, the fix is simple and paves the way for better security. More importantly, it reminds us that in the cloud, even automated systems still rely on deliberate human oversight to keep working smoothly.
By modernizing authentication plugins and staying proactive with compatibility reviews, you ensure your Cloud SQL environments remain secure, accessible, and free from cryptic errors that bring production traffic to a halt. Happy querying!