Docker Swarm’s default network MTU is 1500 , and if the underlying network has a lower MTU than this then any containers on the overlay network will fail to communicate with each other. This would affect all Swarm services.
The solution to this is to adjust Docker Swarm’s MTU to match that of the underlying network. First, you’ll want to determine what the MTU of your network is. On Linux, you can find this with the following command: ip a
This will list the networks available on your server. Locate the network that your nodes communicate over and note the value after mtu . For example:
5: ens10: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc pfifo_fast state UP group default qlen 1000
In the above, the MTU is set to 1450
To use this new MTU, you will first need to remove and recreate the ingress network with the new value. You can use the following commands to achieve this:
docker network rm ingress
docker network create -d overlay --ingress --opt com.docker.network.driver.mtu=1450 ingress
Then, when you are creating new networks you will need to set the MTU to match. For example, in a compose file:
networks:
default:
driver: overlay
driver_opts:
com.docker.network.driver.mtu: 1450