Debugging connection issues


Generally, connection issues fall into one of the following three areas:

  • Connecting - are you able to reach your instance over the network?
  • Authorizing - are you authorized to connect to the instance?
  • Authenticating - does the database accept your database credentials?

Each of those can be further broken down into different paths for investigation. The following section includes examples of questions you can ask yourself to help further narrow down the issue:

Connection issues checklist

Error messages

For specific API error messages, see the Error messages reference page.

Additional connectivity troubleshooting

For other issues, see the Connectivity section in the troubleshooting page.

Common connection issues

Verify that your application is closing connections properly

If you see errors containing "Aborted connection nnnn to db:", it usually indicates that your application is not stopping connections properly. Network issues can also cause this error. The error does not mean that there are problems with your Cloud SQL instance. You are also encouraged to run tcpdump to inspect the packets to track down the source of the problem.

For examples of best practices for connection management, see Managing database connections.

Verify that your certificates have not expired

If your instance is configured to use SSL, go to the Cloud SQL Instances page in the Cloud Console and open the instance. Open its Connections page, select the Security tab and make sure that your server certificate is valid. If it has expired, you must add a new certificate and rotate to it.

Verify that you are authorized to connect

If your connections are failing, check that you are authorized to connect:

  • If you are having trouble connecting using an IP address, for example, you are connecting from your on-premises environment with the mysql client, then make sure that the IP address you are connecting from is authorized to connect to the Cloud SQL instance.

    Connections to a Cloud SQL instance using a private IP address are automatically authorized for RFC 1918 address ranges. This way, all private clients can access the database without going through the Cloud SQL Auth proxy. Non-RFC 1918 address ranges must be configured as authorized networks.

    Cloud SQL doesn't learn Non-RFC 1918 subnet routes from your VPC by default. You need to update the network peering to Cloud SQL to export any Non-RFC 1918 routes. For example:

    gcloud compute networks peerings update cloudsql-mysql-googleapis-com \
    --network=NETWORK \
    --export-subnet-routes-with-public-ip \
  • Here's your current IP address.

  • Try the gcloud sql connect command to connect to your instance. This command authorizes your IP address for a short time. You can run this command in an environment with Cloud SDK and mysql client installed. You can also run this command in Cloud Shell, which is available in the Google Cloud Console and has Cloud SDK and the mysql client pre-installed. Cloud Shell provides a Compute Engine instance that you can use to connect to Cloud SQL.
  • Temporarily allow all IP addresses to connect to an instance. For IPv4 authorize (for IPv6, authorize ::/0.

Verify how you connect

If you get an error message like:

ERROR 1045 (28000): Access denied for user 'root'@'' (using password: NO)

when you connect, verify that you are providing a password.

If you get an error message like:

ERROR 1045 (28000): Access denied for user 'root'@'' (using password: YES)

when you connect, verify that you are using the correct password and that you are connecting over SSL if the instance requires it.

Determining how connections are being initiated

You can see information about your current connections by connecting to your database and running the following command:


Connections that show an IP address, such as, are connecting using IP. Connections with cloudsqlproxy~ are using the Cloud SQL Auth proxy, or else they originated from App Engine. Connections from localhost may be used by some internal Cloud SQL processes.

Understanding connection limits

There are no QPS limits for Cloud SQL instances. However, there are connection, size, and App Engine specific limits in place. See Quotas and Limits.

Database connections consume resources on the server and the connecting application. Always use good connection management practices to minimize your application's footprint and reduce the likelihood of exceeding Cloud SQL connection limits. For more information, see Managing database connections.

Show connections and threads

If you get the "too many connections" error message, or want to find out what is happening on an instance, you can show the number of connections and threads with SHOW PROCESSLIST.

From a MySQL client, run:


You get output similar to the following:

| Id | User      | Host         | db        | Command | Time | State | Info                 |
|  3 | user-name | client-IP    | NULL      | Query   |    0 | NULL  | SHOW processlist     |
|  5 | user-name | client-IP    | guestbook | Sleep   |    1 |       | SELECT * from titles |
| 17 | user-name | client-IP    | employees | Query   |    0 | NULL  | SHOW processlist     |
3 rows in set (0.09 sec)

For information about how to interpret the columns returned from PROCESSLIST, see the MySQL reference.

To get a thread count, you can use:

mysql> SHOW STATUS WHERE Variable_name = 'Threads_connected';

You get output similar to the following:

| Variable_name     | Value |
| Threads_connected | 7     |
1 row in set (0.08 sec)

Connections timeout (from Compute Engine)

Connections with a Compute Engine instance timeout after 10 minutes of inactivity, which can affect long-lived unused connections between your Compute Engine instance and your Cloud SQL instance. For more information, see Networking and Firewalls in the Compute Engine documentation.

To keep long-lived unused connections alive, you can set the TCP keepalive. The following commands set the TCP keepalive value to one minute and make the configuration permanent across instance reboots.

Display the current tcp_keepalive_time value.

cat /proc/sys/net/ipv4/tcp_keepalive_time

Set tcp_keepalive_time to 60 seconds and make it permanent across reboots.

echo 'net.ipv4.tcp_keepalive_time = 60' | sudo tee -a /etc/sysctl.conf

Apply the change.

sudo /sbin/sysctl --load=/etc/sysctl.conf

Display the tcp_keepalive_time value to verify the change was applied.

cat /proc/sys/net/ipv4/tcp_keepalive_time

Connecting with IPv6

If you get either of the error messages

Can't connect to MySQL server on '2001:1234::4321' (10051)
Can't connect to MySQL server on '2001:1234::4321' (101)

when you connect it is likely that you are attempting to connect to the IPv6 address of your instance but do not have IPv6 available on your workstation. You can verify whether IPv6 is functional on your workstation by going to If it does not load then you do not have IPv6 available. Connect to the IPv4 address or your Cloud SQL instance instead. You may need to add an IPv4 address to your instance first.

Occasional connection failures (Legacy HA)

When Cloud SQL restarts an instance due to maintenance events, connections might be routed to the failover replica. When connecting to the failover replica:

  • Read requests from clients using unencrypted connections succeed as normal. However, write requests fail and return an error message, such as 'Error 1290: The MySQL server is running with the --read-only option so it cannot execute this statement.'
  • Read and write requests from clients using encrypted connections fail and return an error message, such as 'x509: certificate is valid for master-instance, not failover-instance.'

After the event is over, Cloud SQL resets the connection. Retry the connection. We recommend that you design your applications to handle occasional connection failures by implementing an error handling strategy like exponential backoff. See Application implementation for more information.

Tools for debugging connectivity


The tcpdump is a tool to capture packets. It is highly encouraged to run tcpdump to capture and inspect the packets between your host and the CloudSQL instances when you are debugging the connectivity problems.

Locate your local IP address

If you don't know the local address of your host, then run the ip -br address show command. On Linux, this shows the network interface, the status of the interface, the local IP, and MAC addresses. For example: eth0 UP fe80::4001:aff:fe80:7/64.

Alternatively, you can run ipconfig or ifconfig to see the status of your network interfaces.

Testing with Connectivity Test

Connectivity Test is a diagnostics tool that lets you check connectivity between endpoints in your network. It analyzes your configuration and in some cases performs run-time verification. It supports Cloud SQL now. Follow these instructions to run tests with your Cloud SQL instances.

Testing your connection

You can use the mysql client to test your ability to connect from your local environment. For more information, see Connecting the mysql client using IP addresses and Connecting the mysql client using the Cloud SQL Auth proxy.

Determining the IP address for your application

To determine the IP address of a computer running your application so you can authorize access to your Cloud SQL instance from that address, use one of the following options:

  • If the computer is not behind a proxy or firewall, log in to the computer and use the What is my IP? site to determine its IP address.
  • If the computer is behind a proxy or firewall, log in to the computer and use a tool or service like to determine its true IP address.

Open local ports

To verify that your host is listening on the ports you think it is, run the ss -tunlp4 command. This tells you what ports are open and listening. For example, if you have a MySQL database running, then port 3306 should be up and listening. For SSH, you should see port 22.

All local port activity

Use the netstat command to see all the local port activity. For example, netstat -lt shows all the currently active ports.

Connect to your Cloud SQL instance using telnet

To verify that you can connect to your Cloud SQL instance using TCP, run the telnet command. Telnet attempts to connect to the IP address and port you give it.

If your Cloud SQL instance is running a MySQL database, for example, then you should be able to telnet to it on port 3306: telnet 3306.

On success, you see the following:


Connected to .

On failure, you see telnet hangs until you force-close the attempt:


^C. .

Cloud Logging

Cloud SQL and Cloud SQL use Cloud Logging. See the Cloud Logging documentation for complete information and review the Cloud SQL sample queries.

View logs

You can view logs for Cloud SQL instances and other Google Cloud projects such as Cloud VPN or Compute Engine instances. To view logs for your Cloud SQL instance log entries:


  1. In the Google Cloud Console, go to the Cloud Logging page.

    Go to Cloud Logging

  2. Select an existing Cloud SQL project at the top of the page.
  3. In the Query builder, add the following:
    • Resource: Select Cloud SQL Database. In the dialog, select a Cloud SQL instance.
    • Log names: Scroll to the Cloud SQL section and select appropriate log files for your instance. For example:
    • Severity: Select a log level.
    • Time range: Select a preset or create a custom range.


Use the gcloud logging command to view log entries. In the example below, replace PROJECT_ID. The limit flag is an optional parameter that indicates the maximum number of entries to return.

gcloud logging read "projects/PROJECT_ID/logs/" \

Private IP addresses

Connections to a Cloud SQL instance using a private IP address are automatically authorized for RFC 1918 address ranges. Non-RFC 1918 address ranges must be configured in Cloud SQL as authorized networks. You also need to update the network peering to Cloud SQL to export any Non-RFC 1918 routes. For example:

gcloud compute networks peerings update cloudsql-mysql-googleapis-com 

The IP range is reserved for the Docker bridge network. Any Cloud SQL instances created with an IP address in that range will be unreachable. Connections from any IP address within that range to Cloud SQL instances using private IP address will fail.

VPN troubleshooting

See the Cloud VPN troubleshooting page.