Host Firewall
This document serves as an introduction to Cilium’s host firewall, to enforce security policies for Kubernetes nodes.
Video
You can also watch a video of Cilium’s host firewall in action on eCHO Episode 40: Cilium Host Firewall.
Enable the Host Firewall in Cilium
Download the Cilium release tarball and change to the kubernetes install directory:
curl -LO https://github.com/cilium/cilium/archive/main.tar.gz tar xzf main.tar.gz cd cilium-main/install/kubernetes
Deploy Cilium release via Helm:
helm install cilium ./cilium \
--namespace kube-system \
--set hostFirewall.enabled=true \
--set devices='{ethX,ethY}'
The devices flag refers to the network devices Cilium is configured on,
such as eth0. If you omit this option, Cilium auto-detects what interfaces
the host firewall applies to.
At this point, the Cilium-managed nodes are ready to enforce network policies.
Attach a Label to the Node
In this guide, host policies only apply to nodes with the label
node-access=ssh. Therefore, you first need to attach this label to a node
in the cluster:
$ export NODE_NAME=k8s1
$ kubectl label node $NODE_NAME node-access=ssh
node/k8s1 labeled
Enable Policy Audit Mode for the Host Endpoint
Host Policies enforce access control over connectivity to and from nodes.
Particular care must be taken to ensure that when host policies are imported,
Cilium does not block access to the nodes or break the cluster’s normal
behavior (for example by blocking communication with kube-apiserver).
To avoid such issues, switch the host firewall in audit mode and validate the impact of host policies before enforcing them.
Warning
When Policy Audit Mode is enabled, no network policy is enforced so this setting is not recommended for production deployment.
Enable and check status for the Policy Audit Mode on the host endpoint for a given node with the following commands:
$ CILIUM_NAMESPACE=kube-system
$ CILIUM_POD_NAME=$(kubectl -n $CILIUM_NAMESPACE get pods -l "k8s-app=cilium" -o jsonpath="{.items[?(@.spec.nodeName=='$NODE_NAME')].metadata.name}")
$ alias kexec="kubectl -n $CILIUM_NAMESPACE exec $CILIUM_POD_NAME --"
$ HOST_EP_ID=$(kexec cilium-dbg endpoint list -o jsonpath='{[?(@.status.identity.id==1)].id}')
$ kexec cilium-dbg endpoint config $HOST_EP_ID PolicyAuditMode=Enabled
Endpoint 3353 configuration updated successfully
$ kexec cilium-dbg endpoint config $HOST_EP_ID | grep PolicyAuditMode
PolicyAuditMode : Enabled
Apply a Host Network Policy
Host Policies match on node labels using a Node Selector to identify the nodes to which the policies applies. They apply only to the host namespace, including host-networking pods. They don’t apply to communications between pods or between pods and the outside of the cluster, except if those pods are host-networking pods.
The following policy applies to all nodes with the node-access=ssh label.
It allows communications from outside the cluster only for TCP/22 and for ICMP
(ping) echo requests. All communications from the cluster to the hosts are
allowed.
apiVersion: "cilium.io/v2"
kind: CiliumClusterwideNetworkPolicy
metadata:
name: "demo-host-policy"
spec:
description: ""
nodeSelector:
matchLabels:
node-access: ssh
ingress:
- fromEntities:
- cluster
- toPorts:
- ports:
- port: "22"
protocol: TCP
- icmps:
- fields:
- type: EchoRequest
family: IPv4
To apply this policy, run:
$ kubectl create -f https://raw.githubusercontent.com/cilium/cilium/HEAD/examples/policies/host/demo-host-policy.yaml ciliumclusterwidenetworkpolicy.cilium.io/demo-host-policy created
The host is represented as a special endpoint, with label reserved:host, in
the output of command cilium-dbg endpoint list. Use this command to inspect
the status of host policies:
$ kexec cilium-dbg endpoint list
ENDPOINT POLICY (ingress) POLICY (egress) IDENTITY LABELS (source:key[=value]) IPv6 IPv4 STATUS
ENFORCEMENT ENFORCEMENT
266 Disabled Disabled 104 k8s:io.cilium.k8s.policy.cluster=default f00d::a0b:0:0:ef4e 10.16.172.63 ready
k8s:io.cilium.k8s.policy.serviceaccount=coredns
k8s:io.kubernetes.pod.namespace=kube-system
k8s:k8s-app=kube-dns
1687 Disabled (Audit) Disabled 1 k8s:node-access=ssh ready
reserved:host
3362 Disabled Disabled 4 reserved:health f00d::a0b:0:0:49cf 10.16.87.66 ready
In this example, one can observe that policy enforcement on the host endpoint is in audit mode for ingress traffic, and disabled for egress traffic.
Adjust the Host Policy to Your Environment
As long as the host endpoint runs in audit mode, communications disallowed by
the policy are not dropped. Nevertheless, they are reported by cilium-dbg
monitor, as action audit. With these reports, the audit mode allows you
to adjust the host policy to your environment in order to avoid unexpected
connection breakages.
$ kexec cilium-dbg monitor -t policy-verdict --related-to $HOST_EP_ID
Policy verdict log: flow 0x0 local EP ID 1687, remote ID 6, proto 1, ingress, action allow, match L3-Only, 192.168.60.12 -> 192.168.60.11 EchoRequest
Policy verdict log: flow 0x0 local EP ID 1687, remote ID 6, proto 6, ingress, action allow, match L3-Only, 192.168.60.12:37278 -> 192.168.60.11:2379 tcp SYN
Policy verdict log: flow 0x0 local EP ID 1687, remote ID 2, proto 6, ingress, action audit, match none, 10.0.2.2:47500 -> 10.0.2.15:6443 tcp SYN
For details on deriving the network policies from the output of cilium
monitor, refer to Observe policy verdicts and Create the Network Policy in
the Creating Policies from Verdicts guide.
Note that Entities Based rules are convenient when combined with host
policies, for example to allow communication to entire classes of destinations,
such as all remotes nodes (remote-node) or the entire cluster
(cluster).
Warning
Make sure that none of the communications required to access the cluster or
for the cluster to work properly are denied. Ensure they all appear as
action allow before disabling the audit mode.
Disable Policy Audit Mode
Once you are confident all required communications to the host from outside the cluster are allowed, disable the policy audit mode to enforce the host policy:
$ kexec cilium-dbg endpoint config $HOST_EP_ID PolicyAuditMode=Disabled
Endpoint 3353 configuration updated successfully
Ingress host policies should now appear as enforced:
$ kexec cilium-dbg endpoint list
ENDPOINT POLICY (ingress) POLICY (egress) IDENTITY LABELS (source:key[=value]) IPv6 IPv4 STATUS
ENFORCEMENT ENFORCEMENT
266 Disabled Disabled 104 k8s:io.cilium.k8s.policy.cluster=default f00d::a0b:0:0:ef4e 10.16.172.63 ready
k8s:io.cilium.k8s.policy.serviceaccount=coredns
k8s:io.kubernetes.pod.namespace=kube-system
k8s:k8s-app=kube-dns
1687 Enabled Disabled 1 k8s:node-access=ssh ready
reserved:host
3362 Disabled Disabled 4 reserved:health f00d::a0b:0:0:49cf 10.16.87.66 ready
Communications that are not explicitly allowed by the host policy are now dropped:
$ kexec cilium-dbg monitor -t policy-verdict --related-to $HOST_EP_ID
Policy verdict log: flow 0x0 local EP ID 1687, remote ID 2, proto 6, ingress, action deny, match none, 10.0.2.2:49038 -> 10.0.2.15:21 tcp SYN
Clean up
$ kubectl delete ccnp demo-host-policy
$ kubectl label node $NODE_NAME node-access-
Further Reading
Read the documentation on Host Policies for additional details on how to use the policies. In particular, refer to the Troubleshooting Host Policies subsection to understand how to debug issues with Host Policies, or to the section on Host Policies known issues to understand the current limitations of the feature.