mysql -> "too many connections"

[philkunz]

Got some fairly popular projects on cloudron. With stuff getting more popular, I run more and more into problems where databases lock up because of "too many connections" Whats happening there?

[james]

Hello @philkunz
Can you please share the logs of the database that logs this?

[philkunz]

May 30 20:34:50 2026-05-30T18:34:50Z
May 30 20:34:50 Error Code:
May 30 20:34:50 Error Code:
May 30 20:34:50
May 30 20:34:50
May 30 20:34:50 Host '[REDACTED_IPV6]' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'
May 30 20:34:50 Host '[REDACTED_IPV6]' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'
May 30 20:34:50
May 30 20:34:50
May 30 20:34:50 ----------------------------------------
May 30 20:34:50 ----------------------------------------
May 30 20:34:50 ER_HOST_IS_BLOCKED
May 30 20:34:50 ER_HOST_IS_BLOCKED
May 30 20:34:50 Error: Host '[REDACTED_IPV6]' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'
May 30 20:34:50 Error: Host '[REDACTED_IPV6]' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'
May 30 20:34:50

[james]

Hello @philkunz
The issue is not actually to too many connections, the issue is that [REDACTED_IPV6] is getting blocked because it creating to many connection erros.
You have to figure out why this IPv6 is creating these connections errors.

[philkunz]

@james The host is the app though, or?

[philkunz]

its essentially just a sign of an app serving many requests, and thereby hammering the db? Or not?

[james]

Hello @philkunz
I can't tell what is accessing your MySQL Service, but if you use Cloudron in the default and not something out of the ordinary, it should be some app.

To get details about the hosts and connection errors, ssh into your Cloudron server, then run:

docker exec -it mysql bash -c 'mysql --user=root --password=$CLOUDRON_MYSQL_ROOT_PASSWORD --execute="SELECT * FROM performance_schema.host_cache"'

This will show all.

If you want to filter for the connection error specifically, run:

docker exec -it mysql bash -c 'mysql --user=root --password=$CLOUDRON_MYSQL_ROOT_PASSWORD --execute="SELECT HOST, SUM_CONNECT_ERRORS FROM performance_schema.host_cache WHERE SUM_CONNECT_ERRORS > 0;"'

it will create an output like:

mysql: [Warning] Using a password on the command line interface can be insecure.
+-----------------+--------------------+
| HOST            | SUM_CONNECT_ERRORS |
+-----------------+--------------------+
| my-cloudron-dev |                  1 |
+-----------------+--------------------+

You can also filter for the amount of auth errors with something like this:

docker exec mysql bash -c 'mysql --user=root --password=$CLOUDRON_MYSQL_ROOT_PASSWORD --execute="SELECT HOST, IP, SUM_CONNECT_ERRORS, COUNT_AUTHENTICATION_ERRORS FROM performance_schema.host_cache \G;"'

Which will return something like this:

*************************** 1. row ***************************
                       HOST: my-cloudron-dev
                         IP: fd00:c107:d509::1
         SUM_CONNECT_ERRORS: 0
COUNT_AUTHENTICATION_ERRORS: 40
*************************** 2. row ***************************
                       HOST: mysql
                         IP: fd00:c107:d509::5
         SUM_CONNECT_ERRORS: 0
COUNT_AUTHENTICATION_ERRORS: 17
*************************** 3. row ***************************
                       HOST: mysql
                         IP: 172.18.30.1
         SUM_CONNECT_ERRORS: 0
COUNT_AUTHENTICATION_ERRORS: 1
*************************** 4. row ***************************
                       HOST: my-cloudron-dev
                         IP: 172.18.0.1
         SUM_CONNECT_ERRORS: 1
COUNT_AUTHENTICATION_ERRORS: 2

There you can see I intentionally failed to connect many times from inside a Cloudron app by running:

for i in {1..20}; do mysql --user=${CLOUDRON_MYSQL_USERNAME} --password=WRONGPASSWORD --host=${CLOUDRON_MYSQL_HOST} ${CLOUDRON_MYSQL_DATABASE}; done

When running this again from inside a Cloudron app, I can run the above MySQL query again and can see:

*************************** 1. row ***************************
                       HOST: my-cloudron-dev
                         IP: fd00:c107:d509::1
         SUM_CONNECT_ERRORS: 0
COUNT_AUTHENTICATION_ERRORS: 60

Is now 60 and was before 40.

If this value keeps rising, without you doing anything manually.
There is some app that is failing to connect to the MySQL service for some reason.
My first suspect would be some WordPress developer app or a restored app that has old credentials from before the restore.