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Creating multi-server clusters

Important note

For the best results (and less unexpected issues), choose 1, 3, 5, … server nodes. (Read more on etcd quorum on At least 2 cores and 4GiB of RAM are recommended.

Embedded etcd

Create a cluster with 3 server nodes using k3s’ embedded etcd database. The first server to be created will use the --cluster-init flag and k3d will wait for it to be up and running before creating (and connecting) the other server nodes.

k3d cluster create multiserver --servers 3

Restarting cluster may fail

When you restart the cluster, each node’s IP (meaning the underlying container’s IP) could change. In this situation, a node might fail to join the existing cluster and consequently fail to start. To address this, you can use the experimental IPAM (IP Address Management) feature to assign each container a static IP. To enable this, create the cluster with the --subnet auto or --subnet (or whatever subnet you need) flags. With --subnet auto, k3d will create a fake docker network to get an available subnet.

See the relavent issue #550 for more details.

Adding server nodes to a running cluster

In theory (and also in practice in most cases), this is as easy as executing the following command:

k3d node create newserver --cluster multiserver --role server

There’s a trap!

If your cluster was initially created with only a single server node, then this will fail.
That’s because the initial server node was not started with the --cluster-init flag and thus is not using the etcd backend.

Last update: July 4, 2024