On Friday, April 22nd, 2022 at 12:20 UTC, Slido users experienced errors and/or increased latency for around 45 minutes. We’d like to apologize to our customers who were impacted by this disruption. There was no impact to your data and Slido’s security wasn’t breached by this incident.
Rest assured that we are taking several actions to improve the resiliency and performance of our service to prevent this type of problem happening again.
This incident was triggered by continuous, machine-generated requests sent to one of our API endpoints in our EU cluster. The nature and volume of this adverse traffic led to the
max_prepared_stmt_count limit  on our MySQL database being reached. As a result, subsequent requests started failing.
We detected the incident through our monitoring at 12:27 UTC. At 12:48 UTC, we manually blocked the source of the adverse traffic on our firewall. At this stage the value for our
max_prepared_stmt_count limit  was increased.
At 12:59 UTC, we blocked a second batch of IP addresses and the
max_prepared_stmt_count value was increased again. The incident was fully resolved at 13:05 UTC.
We are taking the following actions to ensure this does not happen again:
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