When an agent joins a
k3s cluster, the agent generates a password that the server stores for future authentication requests, based on the hostname. Reinstalling
k3s to that agent will throw
403s as the newly generated password obviously won’t match what the server has stored from the previous installation.
Delete the relevant password stored in
/var/lib/rancher/k3s/server/cred/passwd so that the new agent installation can successfully hand the server the newly generated password.