Listen block vs frontend/backend block problem

Help!
1

Hi, Im trying to get a ‘frontend/backend’ proxy block set up to work the same as my existing (successfully working) ‘listen’ proxy block (for kubectl access a kubernetes cluster)

The following ‘listen’ block works absolutely fine for my kubectl utility

listen k8s
  bind *:8383
  mode tcp
  option log-health-checks
  timeout client 3h
  timeout server 3h
  server lab11 10.43.9.1:6443 check check-ssl verify none inter 10000
  server lab13 10.43.9.2:6443 check check-ssl verify none inter 10000
  server lab15 10.43.9.3:6443 check check-ssl verify none inter 10000
  balance roundrobin

But when i set the following ‘frontend/backend’ proxy block up to do the same, my kubectl command returns “Unable to connect to the server: http: server gave HTTP response to HTTPS client”

frontend k8s
    mode tcp
    bind *:8383
    default_backend k8s
    timeout client 3h
    timeout server 3h
    option log-health-checks

backend k8s
    server lab11 10.43.9.1:6443 check check-ssl verify none inter 10000
    server lab13 10.43.9.2:6443 check check-ssl verify none inter 10000
    server lab15 10.43.9.3:6443 check check-ssl verify none inter 10000
    balance roundrobin

Does anyone have any idea what im doing wrong here? As far as I was aware, I can use a ‘frontend/backend’ proxy block in the same way …am i missing some parameters ?

Any help would be greatly appreciated