SUSE Cloud/Docker

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MTU problems

When deploying SUSE OpenStack Cloud with the default settings, you get openvswitch with gre tunnels. The gre headers eat away some byte of your maximum transfer unit (MTU), so VMs will then only be able to transmit 1450 byte at a time instead of 1500. This causes some issues with docker.

using docker in a cloud

Workaround1

edit /etc/sysconfig/docker and set

DOCKER_OPTS="--mtu=1450"

Workaround2

Use iptables to limit tcp sizes in the cloud instance VM - probably like this:

iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS  --clamp-mss-to-pmtu


or something like

iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 1320


using docker-compose in a cloud

see https://github.com/docker/docker/issues/22297#issuecomment-242934050