When using docker in cloud platforms (based on OpenStack or custom platforms like Hetzner) it is common to work with MTU size less than 1500.
If you’re using docker in such an environment, connections from docker containers to outside world will be failed when using big packets.
In this case MTU must be set in docker configuration. For example if your cloud provider uses MTU size of 1400, it must be configured in /etc/docker/daemon.json as below:
{
"mtu": 1400
}