Kubernetes without kube-proxy

This guide explains how to provision a Kubernetes cluster without kube-proxy, and to use Cilium to fully replace it. For simplicity, we will use kubeadm to bootstrap the cluster.

For installing kubeadm and for more provisioning options please refer to the official kubeadm documentation.

Note

Cilium’s kube-proxy replacement depends on the Host-Reachable Services feature, therefore a v4.19.57, v5.1.16, v5.2.0 or more recent Linux kernel is required. Linux kernels v5.3 and v5.8 add additional features that Cilium can use to further optimize the kube-proxy replacement implementation.

Note that v5.0.y kernels do not have the fix required to run the kube-proxy replacement since at this point in time the v5.0.y stable kernel is end-of-life (EOL) and not maintained anymore on kernel.org. For individual distribution maintained kernels, the situation could differ. Therefore, please check with your distribution.

Quick-Start

Initialize the control-plane node via kubeadm init, set a pod network CIDR and skip the kube-proxy add-on:

kubeadm init --skip-phases=addon/kube-proxy

In K8s 1.15 and older it is not yet possible to disable kube-proxy via --skip-phases=addon/kube-proxy in kubeadm, therefore the below workaround for manually removing the kube-proxy DaemonSet and cleaning the corresponding iptables rules after kubeadm initialization is still necessary (kubeadm#1733).

Initialize control-plane as first step:

kubeadm init

Then delete the kube-proxy DaemonSet and remove its iptables rules as following:

kubectl -n kube-system delete ds kube-proxy
iptables-restore <(iptables-save | grep -v KUBE)

For existing installations with kube-proxy running as a DaemonSet, remove it by using the following commands:

kubectl -n kube-system delete ds kube-proxy
# Run on each node:
iptables-restore <(iptables-save | grep -v KUBE)

Afterwards, join worker nodes by specifying the control-plane node IP address and the token returned by kubeadm init:

kubeadm join <..>

Note

Please ensure that kubelet’s --node-ip is set correctly on each worker if you have multiple interfaces. Cilium’s kube-proxy replacement may not work correctly otherwise. You can validate this by running kubectl get nodes -o wide to see whether each node has an InternalIP which is assigned to a device with the same name on each node.

Note

First, make sure you have Helm 3 installed.

If you have (or planning to have) Helm 2 charts (and Tiller) in the same cluster, there should be no issue as both version are mutually compatible in order to support gradual migration. Cilium chart is targeting Helm 3 (v3.0.3 and above).

Setup Helm repository:

helm repo add cilium https://helm.cilium.io/

Next, generate the required YAML files and deploy them. Important: Replace REPLACE_WITH_API_SERVER_IP and REPLACE_WITH_API_SERVER_PORT below with the concrete control-plane node IP address and the kube-apiserver port number reported by kubeadm init (usually, it is port 6443).

Specifying this is necessary as kubeadm init is run explicitly without setting up kube-proxy and as a consequence while it exports KUBERNETES_SERVICE_HOST and KUBERNETES_SERVICE_PORT with a ClusterIP of the kube-apiserver service to the environment, there is no kube-proxy in our setup provisioning that service. The Cilium agent therefore needs to be made aware of this information through below configuration.

helm install cilium cilium/cilium --version 1.8.5 \
    --namespace kube-system \
    --set global.kubeProxyReplacement=strict \
    --set global.k8sServiceHost=REPLACE_WITH_API_SERVER_IP \
    --set global.k8sServicePort=REPLACE_WITH_API_SERVER_PORT

This will install Cilium as a CNI plugin with the BPF kube-proxy replacement to implement handling of Kubernetes services of type ClusterIP, NodePort, LoadBalancer and services with externalIPs. On top of that the BPF kube-proxy replacement also supports hostPort for containers such that using portmap is not necessary anymore.

Finally, as a last step, verify that Cilium has come up correctly on all nodes and is ready to operate:

kubectl -n kube-system get pods -l k8s-app=cilium
NAME                READY     STATUS    RESTARTS   AGE
cilium-fmh8d        1/1       Running   0          10m
cilium-mkcmb        1/1       Running   0          10m

Note, in above helm configuration the kubeProxyReplacement has been set to strict mode. This means that the Cilium agent will bail out in case the underlying Linux kernel support is missing.

Without explicitly specifying a kubeProxyReplacement option, helm uses kubeProxyReplacement with probe by default which would automatically disable a subset of the features to implement the kube-proxy replacement instead of bailing out if the kernel support is missing. This makes the assumption that Cilium’s BPF kube-proxy replacement would co-exist with kube-proxy on the system to optimize Kubernetes services. Given we’ve used kubeadm to explicitly deploy a kube-proxy-free setup, the strict mode has been used instead to ensure that we do not rely on a (non-existing) fallback.

Cilium’s BPF kube-proxy replacement is supported in direct routing as well as in tunneling mode.

Validate the Setup

After deploying Cilium with above Quick-Start guide, we can first validate that the Cilium agent is running in the desired mode:

kubectl exec -it -n kube-system cilium-fmh8d -- cilium status | grep KubeProxyReplacement
KubeProxyReplacement:   Strict      [eth0 (DR), eth1]       [NodePort (SNAT, 30000-32767, XDP: NONE), HostPort, ExternalIPs, HostReachableServices (TCP, UDP)]

As a next, optional step, we deploy nginx pods, create a new NodePort service and validate that Cilium installed the service correctly.

The following yaml is used for the backend pods:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-nginx
spec:
  selector:
    matchLabels:
      run: my-nginx
  replicas: 2
  template:
    metadata:
      labels:
        run: my-nginx
    spec:
      containers:
      - name: my-nginx
        image: nginx
        ports:
        - containerPort: 80

Verify that the nginx pods are up and running:

kubectl get pods -l run=my-nginx -o wide
NAME                        READY   STATUS    RESTARTS   AGE   IP             NODE   NOMINATED NODE   READINESS GATES
my-nginx-756fb87568-gmp8c   1/1     Running   0          62m   10.217.0.149   apoc   <none>           <none>
my-nginx-756fb87568-n5scv   1/1     Running   0          62m   10.217.0.107   apoc   <none>           <none>

In the next step, we create a NodePort service for the two instances:

kubectl expose deployment my-nginx --type=NodePort --port=80
service/my-nginx exposed

Verify that the NodePort service has been created:

kubectl get svc my-nginx
NAME       TYPE       CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
my-nginx   NodePort   10.104.239.135   <none>        80:31940/TCP   24m

With the help of the cilium service list command, we can validate that Cilium’s BPF kube-proxy replacement created the new NodePort services under port 31940 (one for each of devices eth0 and eth1):

kubectl exec -it -n kube-system cilium-fmh8d -- cilium service list
ID   Frontend               Service Type   Backend
[...]
4    10.104.239.135:80      ClusterIP      1 => 10.217.0.107:80
                                           2 => 10.217.0.149:80
5    0.0.0.0:31940          NodePort       1 => 10.217.0.107:80
                                           2 => 10.217.0.149:80
6    192.168.178.29:31940   NodePort       1 => 10.217.0.107:80
                                           2 => 10.217.0.149:80
7    172.16.0.29:31940      NodePort       1 => 10.217.0.107:80
                                           2 => 10.217.0.149:80

At the same time we can inspect through iptables in the host namespace that no iptables rule for the service is present:

iptables-save | grep KUBE-SVC
[ empty line ]

Last but not least, a simple curl test shows connectivity for the exposed NodePort port 31940 as well as for the ClusterIP:

curl 127.0.0.1:31940
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
[....]
curl 192.168.178.29:31940
<!doctype html>
<html>
<head>
<title>welcome to nginx!</title>
[....]
curl 172.16.0.29:31940
<!doctype html>
<html>
<head>
<title>welcome to nginx!</title>
[....]
curl 10.104.239.135:80
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
[....]

As can be seen, the Cilium’s BPF kube-proxy replacement is set up correctly.

Advanced Configuration

This section covers a few advanced configuration modes for the kube-proxy replacement that go beyond the above Quick-Start guide and are entirely optional.

Client Source IP Preservation

Cilium’s BPF kube-proxy replacement implements a number of options in order to avoid performing SNAT on NodePort requests where the client source IP address would otherwise be lost on its path to the service endpoint.

  • externalTrafficPolicy=Local: The Local policy is generally supported through the BPF implementation. In-cluster connectivity for services with externalTrafficPolicy=Local is possible and can also be reached from nodes which have no local backends, meaning, given SNAT does not need to be performed, all service endpoints are available for load balancing from in-cluster side.
  • externalTrafficPolicy=Cluster: For the Cluster policy which is the default upon service creation, multiple options exist for achieving client source IP preservation for external traffic, that is, operating the kube-proxy replacement in DSR or Hybrid mode if only TCP-based services are exposed to the outside world for the latter.

Direct Server Return (DSR)

By default, Cilium’s BPF NodePort implementation operates in SNAT mode. That is, when node-external traffic arrives and the node determines that the backend for the LoadBalancer, NodePort or services with externalIPs is at a remote node, then the node is redirecting the request to the remote backend on its behalf by performing SNAT. This does not require any additional MTU changes at the cost that replies from the backend need to make the extra hop back that node in order to perform the reverse SNAT translation there before returning the packet directly to the external client.

This setting can be changed through the global.nodePort.mode helm option to dsr in order to let Cilium’s BPF NodePort implementation operate in DSR mode. In this mode, the backends reply directly to the external client without taking the extra hop, meaning, backends reply by using the service IP/port as a source. DSR currently requires Cilium to be deployed in Native-Routing, i.e. it will not work in either tunneling mode.

Another advantage in DSR mode is that the client’s source IP is preserved, so policy can match on it at the backend node. In the SNAT mode this is not possible. Given a specific backend can be used by multiple services, the backends need to be made aware of the service IP/port which they need to reply with. Therefore, Cilium encodes this information in a Cilium-specific IPv4 option or IPv6 Destination Option extension header at the cost of advertising a lower MTU. For TCP services, Cilium only encodes the service IP/port for the SYN packet, but not subsequent ones. The latter also allows to operate Cilium in a hybrid mode as detailed in the next subsection where DSR is used for TCP and SNAT for UDP in order to avoid an otherwise needed MTU reduction.

Note that usage of DSR mode might not work in some public cloud provider environments due to the Cilium-specific IP options that could be dropped by an underlying fabric. Therefore, in case of connectivity issues to services where backends are located on a remote node from the node that is processing the given NodePort request, it is advised to first check whether the NodePort request actually arrived on the node containing the backend. If this was not the case, then switching back to the default SNAT mode would be advised as a workaround.

Also, in some public cloud provider environments, which implement a source / destination IP address checking (e.g. AWS), the checking has to be disabled in order for the DSR mode to work.

Above helm example configuration in a kube-proxy-free environment with DSR-only mode enabled would look as follows:

helm install cilium cilium/cilium --version 1.8.5 \
    --namespace kube-system \
    --set global.tunnel=disabled \
    --set global.autoDirectNodeRoutes=true \
    --set global.kubeProxyReplacement=strict \
    --set global.nodePort.mode=dsr \
    --set global.k8sServiceHost=REPLACE_WITH_API_SERVER_IP \
    --set global.k8sServicePort=REPLACE_WITH_API_SERVER_PORT

Hybrid DSR and SNAT Mode

Cilium also supports a hybrid DSR and SNAT mode, that is, DSR is performed for TCP and SNAT for UDP connections. This has the advantage that it removes the need for manual MTU changes in the network while still benefiting from the latency improvements through the removed extra hop for replies, in particular, when TCP is the main transport for workloads.

The mode setting global.nodePort.mode allows to control the behavior through the options dsr, snat and hybrid. By default the snat mode is used in the agent.

A helm example configuration in a kube-proxy-free environment with DSR enabled in hybrid mode would look as follows:

helm install cilium cilium/cilium --version 1.8.5 \
    --namespace kube-system \
    --set global.tunnel=disabled \
    --set global.autoDirectNodeRoutes=true \
    --set global.kubeProxyReplacement=strict \
    --set global.nodePort.mode=hybrid \
    --set global.k8sServiceHost=REPLACE_WITH_API_SERVER_IP \
    --set global.k8sServicePort=REPLACE_WITH_API_SERVER_PORT

LoadBalancer & NodePort XDP Acceleration

Cilium has built-in support for accelerating NodePort, LoadBalancer services and services with externalIPs for the case where the arriving request needs to be pushed back out of the node when the backend is located on a remote node. This ability to act as a “one-legged” / hairpin load balancer can be handled by Cilium starting from version 1.8 at the XDP (eXpress Data Path) layer where BPF is operating directly in the networking driver instead of a higher layer.

The mode setting global.nodePort.acceleration allows to enable this acceleration through the option native. The option disabled is the default and disables the acceleration. The majority of drivers supporting 10G or higher rates also support native XDP on a recent kernel. For cloud based deployments most of these drivers have SR-IOV variants that support native XDP as well. For on-prem deployments the Cilium XDP acceleration can be used in combination with LoadBalancer service implementations for Kubernetes such as MetalLB. The acceleration can be enabled only on a single device which is used for direct routing.

For high-scale environments, also consider tweaking the default map sizes to a larger number of entries e.g. through setting a higher config.bpfMapDynamicSizeRatio. See eBPF Maps for further details.

The global.nodePort.acceleration setting is supported for DSR, SNAT and hybrid modes and can be enabled as follows for nodePort.mode=hybrid in this example:

helm install cilium cilium/cilium --version 1.8.5 \
    --namespace kube-system \
    --set global.tunnel=disabled \
    --set global.autoDirectNodeRoutes=true \
    --set global.kubeProxyReplacement=strict \
    --set global.nodePort.acceleration=native \
    --set global.nodePort.mode=hybrid \
    --set global.k8sServiceHost=REPLACE_WITH_API_SERVER_IP \
    --set global.k8sServicePort=REPLACE_WITH_API_SERVER_PORT

In case of a multi-device environment, where Cilium’s device auto-detection selects more than a single device to expose NodePort, for example, the helm option global.devices=eth0 must be additionally specified for the enablement, where eth0 is the native XDP supported networking device. In that case, the device name eth0 must be the same on all Cilium managed nodes. Similarly, the underlying driver for eth0 must have native XDP support on all Cilium managed nodes.

A list of drivers supporting native XDP can be found in the table below. The corresponding network driver name of an interface can be determined as follows:

# ethtool -i eth0
driver: nfp
[...]
Vendor Driver XDP Support
Amazon ena >= 5.6
Broadcom bnxt_en >= 4.11
Cavium thunderx >= 4.12
Freescale dpaa2 >= 5.0
Intel ixgbe >= 4.12
ixgbevf >= 4.17
i40e >= 4.13
ice >= 5.5
Marvell mvneta >= 5.5
Mellanox mlx4 >= 4.8
mlx5 >= 4.9
Microsoft hv_netvsc >= 5.6
Netronome nfp >= 4.10
Others virtio_net >= 4.10
tun/tap >= 4.14
Qlogic qede >= 4.10
Socionext netsec >= 5.3
Solarflare sfc >= 5.5
Texas Instruments cpsw >= 5.3

The current Cilium kube-proxy XDP acceleration mode can also be introspected through the cilium status CLI command. If it has been enabled successfully, XDP: NATIVE is shown:

kubectl exec -it -n kube-system cilium-xxxxx -- cilium status | grep KubeProxyReplacement
KubeProxyReplacement:   Strict      [eth0 (DR)]     [NodePort (SNAT, 30000-32767, XDP: NATIVE), HostPort, ExternalIPs, HostReachableServices (TCP, UDP)]

In the example above, the NodePort XDP acceleration is enabled on the eth0 device which is also used for direct routing (DR).

Note that packets which have been pushed back out of the device for NodePort handling right at the XDP layer are not visible in tcpdump since packet taps come at a much later stage in the networking stack. Cilium’s monitor or metric counters can be used instead for gaining visibility.

NodePort XDP on AWS

In order to run with NodePort XDP on AWS, follow the instructions in the Installation on AWS EKS guide to set up an EKS cluster or use any other method of your preference to set up a Kubernetes cluster.

If you are following the EKS guide, make sure to create a node group with SSH access, since we need few additional setup steps as well as create a larger instance type which supports the Elastic Network Adapter (ena). As an instance example, m5n.xlarge is used in the config nodegroup-config.yaml:

apiVersion: eksctl.io/v1alpha5
kind: ClusterConfig

metadata:
  name: test-cluster
  region: us-west-2

nodeGroups:
  - name: ng-1
    instanceType: m5n.xlarge
    desiredCapacity: 2
    ssh:
      allow: true

The nodegroup is created with:

eksctl create nodegroup -f nodegroup-config.yaml

Each of the nodes need the kernel-ng and ethtool package installed. The former is needed in order to run a sufficiently recent kernel for eBPF in general and native XDP support on the ena driver. The latter is needed to configure channel parameters for the NIC.

IPS=$(kubectl get no -o jsonpath='{$.items[*].status.addresses[?(@.type=="ExternalIP")].address }{"\n"}' | tr ' ' '\n')

for ip in $IPS ; do ssh ec2-user@$ip "sudo amazon-linux-extras install -y kernel-ng && sudo yum install -y ethtool && sudo reboot"; done

Once the nodes come back up their kernel version should say 5.4.58-27.104.amzn2.x86_64 or similar through uname -r. In order to run XDP on ena, make sure the driver version is at least 2.2.8. The driver version can be inspected through ethtool -i eth0. For the given kernel version the driver version should be reported as 2.2.10g.

Before Cilium’s XDP acceleration can be deployed, there are two settings needed on the network adapter side, that is, MTU needs to be lowered in order to be able to operate with XDP, and number of combined channels need to be adapted.

The default MTU is set to 9001 on the ena driver. Given XDP buffers are linear, they operate on a single page. A driver typically reserves some headroom for XDP as well (e.g. for encapsulation purpose), therefore, the highest possible MTU for XDP would be 3818.

In terms of ena channels, the settings can be gathered via ethtool -l eth0. For the m5n.xlarge instance, the default output should look like:

Channel parameters for eth0:
Pre-set maximums:
RX:             0
TX:             0
Other:          0
Combined:       4
Current hardware settings:
RX:             0
TX:             0
Other:          0
Combined:       4

In order to use XDP the channels must be set to at most 1/2 of the value from Combined above. Both, MTU and channel changes are applied as follows:

for ip in $IPS ; do ssh ec2-user@$ip "sudo ip link set dev eth0 mtu 3818"; done
for ip in $IPS ; do ssh ec2-user@$ip "sudo ethtool -L eth0 combined 2"; done

In order to deploy Cilium, the Kubernetes API server IP and port is needed:

export API_SERVER_IP=$(kubectl get ep kubernetes -o jsonpath='{$.subsets[0].addresses[0].ip}')
export API_SERVER_PORT=443

Finally, the deployment can be upgraded and later rolled-out with the global.nodePort.acceleration=native setting to enable XDP in Cilium:

helm upgrade cilium cilium/cilium --version 1.8.5 \
      --namespace kube-system \
      --reuse-values \
      --set global.autoDirectNodeRoutes=true \
      --set global.kubeProxyReplacement=strict \
      --set global.nodePort.acceleration=native \
      --set global.nodePort.mode=snat \
      --set global.k8sServiceHost=$API_SERVER_IP \
      --set global.k8sServicePort=$API_SERVER_PORT

NodePort XDP on Azure

To enable NodePort XDP on a self-managed Kubernetes running on Azure, the virtual machines running Kubernetes must have Accelerated Networking enabled. In addition, the Linux kernel on the nodes must also have support for native XDP in the hv_netvsc driver, which is available in kernel >= 5.6.

To enable accelerated networking when creating a virtual machine or virtual machine scale set, pass the --accelerated-networking option to the Azure CLI. Please refer to the guide on how to create a Linux virtual machine with Accelerated Networking using Azure CLI for more details.

When Accelerated Networking is enabled, lspci will show a Mellanox ConnectX-3 or ConnectX-4 Lx NIC:

$ lspci | grep Ethernet
2846:00:02.0 Ethernet controller: Mellanox Technologies MT27710 Family [ConnectX-4 Lx Virtual Function] (rev 80)

In order to run XDP, large receive offload (LRO) needs to be disabled on the hv_netvsc device. If not the case already, this can be achieved by:

ethtool -K eth0 lro off

NodePort XDP requires Cilium to run in direct routing mode (tunnel=disabled). It is recommended to use Azure IPAM for the pod IP address allocation, which will automatically configure your virtual network to route pod traffic correctly:

helm install cilium cilium/cilium --version 1.8.5 \
  --namespace kube-system \
  --set config.ipam=azure \
  --set global.azure.enabled=true \
  --set global.azure.resourceGroup=$AZURE_NODE_RESOURCE_GROUP \
  --set global.azure.subscriptionID=$AZURE_SUBSCRIPTION_ID \
  --set global.azure.tenantID=$AZURE_TENANT_ID \
  --set global.azure.clientID=$AZURE_CLIENT_ID \
  --set global.azure.clientSecret=$AZURE_CLIENT_SECRET \
  --set global.tunnel=disabled \
  --set global.masquerade=false \
  --set global.kubeProxyReplacement=strict \
  --set global.nodePort.acceleration=native \
  --set global.nodePort.mode=hybrid \
  --set global.k8sServiceHost=REPLACE_WITH_API_SERVER_IP \
  --set global.k8sServicePort=REPLACE_WITH_API_SERVER_PORT

When running Azure IPAM on a self-managed Kubernetes cluster, each v1.Node must have the resource ID of its VM in the spec.providerID field. Refer to the Azure IPAM (beta) reference for more information.

NodePort Devices, Port and Bind settings

When running Cilium’s BPF kube-proxy replacement, by default, a NodePort or LoadBalancer service or a service with externalIPs will be accessible through the IP addresses of native devices which have the default route on the host or have Kubernetes InternalIP or ExternalIP assigned. InternalIP is preferred over ExternalIP if both exist. To change the devices, set their names in the global.devices helm option, e.g. global.devices='{eth0,eth1,eth2}'. Each listed device has to be named the same on all Cilium managed nodes.

When multiple devices are used, only one device can be used for direct routing between Cilium nodes. By default, if a single device was detected or specified via global.devices then Cilium will use that device for direct routing. Otherwise, Cilium will use a device with Kubernetes InternalIP or ExternalIP being set. InternalIP is preferred over ExternalIP if both exist. To change the direct routing device, set the global.nodePort.directRoutingDevice helm option, e.g. global.nodePort.directRoutingDevice=eth1. If the direct routing device does not exist within global.devices, Cilium will add the device to the latter list. The direct routing device is used for the NodePort XDP acceleration as well (if enabled).

In addition, thanks to the Host-Reachable Services feature, the NodePort service can be accessed by default from a host or a pod within a cluster via its public, any local (except for docker* prefixed names) or loopback address, e.g. 127.0.0.1:NODE_PORT.

If kube-apiserver was configured to use a non-default NodePort port range, then the same range must be passed to Cilium via the global.nodePort.range option, for example, as global.nodePort.range="10000\,32767" for a range of 10000-32767. The default Kubernetes NodePort range is 30000-32767.

If the NodePort port range overlaps with the ephemeral port range (net.ipv4.ip_local_port_range), Cilium will append the NodePort range to the reserved ports (net.ipv4.ip_local_reserved_ports). This is needed to prevent a NodePort service from hijacking traffic of a host local application which source port matches the service port. To disable the modification of the reserved ports, set global.nodePort.autoProtectPortRanges to false.

By default, the NodePort implementation prevents application bind(2) requests to NodePort service ports. In such case, the application will typically see a bind: Operation not permitted error. This happens either globally for older kernels or starting from v5.7 kernels only for the host namespace by default and therefore not affecting any application pod bind(2) requests anymore. In order to opt-out from this behavior in general, this setting can be changed for expert users by switching global.nodePort.bindProtection to false.

Container hostPort support

Although not part of kube-proxy, Cilium’s BPF kube-proxy replacement also natively supports hostPort service mapping without having to use the Helm CNI chaining option of global.cni.chainingMode=portmap.

By specifying global.kubeProxyReplacement=strict or global.kubeProxyReplacement=probe the native hostPort support is automatically enabled and therefore no further action is required. Otherwise global.hostPort.enabled=true can be used to enable the setting.

If the hostPort is specified without an additional hostIP, then the Pod will be exposed to the outside world with the same local addresses from the node that were detected and used for exposing NodePort services, e.g. the Kubernetes InternalIP or ExternalIP if set. Additionally, the Pod is also accessible through the loopback address on the node such as 127.0.0.1:hostPort. If in addition to hostPort also a hostIP has been specified for the Pod, then the Pod will only be exposed on the given hostIP instead. A hostIP of 0.0.0.0 will have the same behavior as if a hostIP was not specified. The hostPort must not reside in the configured NodePort port range to avoid collisions.

An example deployment in a kube-proxy-free environment therefore is the same as in the earlier getting started deployment:

helm install cilium cilium/cilium --version 1.8.5 \
    --namespace kube-system \
    --set global.kubeProxyReplacement=strict \
    --set global.k8sServiceHost=REPLACE_WITH_API_SERVER_IP \
    --set global.k8sServicePort=REPLACE_WITH_API_SERVER_PORT

Also, ensure that each node IP is known via INTERNAL-IP or EXTERNAL-IP, for example:

kubectl get nodes -o wide
NAME   STATUS   ROLES    AGE     VERSION   INTERNAL-IP      EXTERNAL-IP   [...]
apoc   Ready    master   6h15m   v1.17.3   192.168.178.29   <none>        [...]
tank   Ready    <none>   6h13m   v1.17.3   192.168.178.28   <none>        [...]

If this is not the case, then kubelet needs to be made aware of it through specifying --node-ip through KUBELET_EXTRA_ARGS. Assuming eth0 is the public facing interface, this can be achieved by:

echo KUBELET_EXTRA_ARGS="--node-ip=$(ip -4 -o a show eth0 | awk '{print $4}' | cut -d/ -f1)" | tee -a /etc/default/kubelet

After updating /etc/default/kubelet, kubelet needs to be restarted.

In order to verify whether the HostPort feature has been enabled in Cilium, the cilium status CLI command provides visibility through the KubeProxyReplacement info line. If it has been enabled successfully, HostPort is shown, for example:

kubectl exec -it -n kube-system cilium-xxxxx -- cilium status | grep KubeProxyReplacement
KubeProxyReplacement:   Strict   [eth0 (DR)]   [NodePort (SNAT, 30000-32767, XDP: DISABLED), HostPort, ExternalIPs, HostReachableServices (TCP, UDP), SessionAffinity]

The following modified example yaml from the setup validation with an additional hostPort: 8080 parameter can be used to verify the mapping:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-nginx
spec:
  selector:
    matchLabels:
      run: my-nginx
  replicas: 1
  template:
    metadata:
      labels:
        run: my-nginx
    spec:
      containers:
      - name: my-nginx
        image: nginx
        ports:
        - containerPort: 80
          hostPort: 8080

After deployment, we can validate that Cilium’s BPF kube-proxy replacement exposed the container as HostPort under the specified port 8080:

kubectl exec -it -n kube-system cilium-fmh8d -- cilium service list
ID   Frontend               Service Type   Backend
[...]
5    192.168.178.29:8080    HostPort       1 => 10.29.207.199:80

Similarly, we can inspect through iptables in the host namespace that no iptables rule for the HostPort service is present:

iptables-save | grep HOSTPORT
[ empty line ]

Last but not least, a simple curl test shows connectivity for the exposed HostPort container under the node’s IP:

curl 192.168.178.29:8080
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
[....]

Removing the deployment also removes the corresponding HostPort from the cilium service list dump:

kubectl delete deployment my-nginx

kube-proxy Hybrid Modes

Cilium’s BPF kube-proxy replacement can be configured in several modes, i.e. it can replace kube-proxy entirely or it can co-exist with kube-proxy on the system if the underlying Linux kernel requirements do not support a full kube-proxy replacement.

This section therefore elaborates on the various global.kubeProxyReplacement options:

  • global.kubeProxyReplacement=strict: This option expects a kube-proxy-free Kubernetes setup where Cilium is expected to fully replace all kube-proxy functionality. Once the Cilium agent is up and running, it takes care of handling Kubernetes services of type ClusterIP, NodePort, LoadBalancer, services with externalIPs as well as HostPort. If the underlying kernel version requirements are not met (see Kubernetes without kube-proxy note), then the Cilium agent will bail out on start-up with an error message.

  • global.kubeProxyReplacement=probe: This option is intended for a hybrid setup, that is, kube-proxy is running in the Kubernetes cluster where Cilium partially replaces and optimizes kube-proxy functionality. Once the Cilium agent is up and running, it probes the underlying kernel for the availability of needed BPF kernel features and, if not present, disables a subset of the functionality in BPF by relying on kube-proxy to complement the remaining Kubernetes service handling. The Cilium agent will emit an info message into its log in such case. For example, if the kernel does not support Host-Reachable Services, then the ClusterIP translation for the node’s host-namespace is done through kube-proxy’s iptables rules.

  • global.kubeProxyReplacement=partial: Similarly to probe, this option is intended for a hybrid setup, that is, kube-proxy is running in the Kubernetes cluster where Cilium partially replaces and optimizes kube-proxy functionality. As opposed to probe which checks the underlying kernel for available BPF features and automatically disables components responsible for the BPF kube-proxy replacement when kernel support is missing, the partial option requires the user to manually specify which components for the BPF kube-proxy replacement should be used. When global.kubeProxyReplacement is set to partial make sure to also set global.enableHealthCheckNodeport to false, so that the Cilium agent does not start the NodePort health check server. Similarly to strict mode, the Cilium agent will bail out on start-up with an error message if the underlying kernel requirements are not met. For fine-grained configuration, global.hostServices.enabled, global.nodePort.enabled, global.externalIPs.enabled and global.hostPort.enabled can be set to true. By default all four options are set to false. A few example configurations for the partial option are provided below.

    The following helm setup below would be equivalent to global.kubeProxyReplacement=strict in a kube-proxy-free environment:

    helm install cilium cilium/cilium --version 1.8.5 \
        --namespace kube-system \
        --set global.kubeProxyReplacement=partial \
        --set global.hostServices.enabled=true \
        --set global.nodePort.enabled=true \
        --set global.externalIPs.enabled=true \
        --set global.hostPort.enabled=true \
        --set global.k8sServiceHost=REPLACE_WITH_API_SERVER_IP \
        --set global.k8sServicePort=REPLACE_WITH_API_SERVER_PORT
    

    The following helm setup below would be equivalent to the default Cilium service handling in v1.6 or earlier in a kube-proxy environment, that is, serving ClusterIP for pods:

    helm install cilium cilium/cilium --version 1.8.5 \
        --namespace kube-system \
        --set global.kubeProxyReplacement=partial
    

    The following helm setup below would optimize Cilium’s ClusterIP handling for TCP in a kube-proxy environment (global.hostServices.protocols default is tcp,udp):

    helm install cilium cilium/cilium --version 1.8.5 \
        --namespace kube-system \
        --set global.kubeProxyReplacement=partial \
        --set global.hostServices.enabled=true \
        --set global.hostServices.protocols=tcp
    

    The following helm setup below would optimize Cilium’s NodePort, LoadBalancer and services with externalIPs handling for external traffic ingressing into the Cilium managed node in a kube-proxy environment:

    helm install cilium cilium/cilium --version 1.8.5 \
        --namespace kube-system \
        --set global.kubeProxyReplacement=partial \
        --set global.nodePort.enabled=true \
        --set global.externalIPs.enabled=true
    
  • global.kubeProxyReplacement=disabled: This option disables any Kubernetes service handling by fully relying on kube-proxy instead, except for ClusterIP services accessed from pods if cilium-agent’s flag --disable-k8s-services is set to false (pre-v1.6 behavior).

In Cilium’s helm chart, the default mode is global.kubeProxyReplacement=probe for new deployments.

For existing Cilium deployments in version v1.6 or prior, please consult the 1.7 Upgrade Notes.

The current Cilium kube-proxy replacement mode can also be introspected through the cilium status CLI command:

kubectl exec -it -n kube-system cilium-xxxxx -- cilium status | grep KubeProxyReplacement
KubeProxyReplacement:   Strict      [eth0 (DR)]     [NodePort (SNAT, 30000-32767, XDP: NONE), HostPort, ExternalIPs, HostReachableServices (TCP, UDP)]

Session Affinity

Cilium’s BPF kube-proxy replacement supports Kubernetes service session affinity. Each connection from the same pod or host to a service configured with sessionAffinity: ClientIP will always select the same service endpoint. The default timeout for the affinity is three hours (updated by each request to the service), but it can be configured through Kubernetes’ sessionAffinityConfig if needed.

The source for the affinity depends on the origin of a request. If a request is sent from outside the cluster to the service, the request’s source IP address is used for determining the endpoint affinity. If a request is sent from inside the cluster, the client’s network namespace cookie is used. The latter was introduced in the 5.7 Linux kernel to implement the affinity at the socket layer at which Host-Reachable Services operate (a source IP is not available there, as the endpoint selection happens before a network packet has been built by the kernel).

The session affinity support is enabled by default for Cilium’s kube-proxy replacement. For users who run on older kernels which do not support the network namespace cookies, a fallback in-cluster mode is implemented, which is based on a fixed cookie value as a trade-off. This makes all applications on the host to select the same service endpoint for a given service with session affinity configured. To disable the feature, set config.sessionAffinity=false.

LoadBalancer Source Ranges Checks

When a LoadBalancer service is configured with spec.loadBalancerSourceRanges, Cilium’s eBPF kube-proxy replacement restricts access from outside (e.g. external world traffic) to the service to the white-listed CIDRs specified in the field. If the field is empty, no restrictions for the access will be applied.

When accessing the service from inside a cluster, the kube-proxy replacement will ignore the field regardless whether it is set. This means that any pod or any host process in the cluster will be able to access the LoadBalancer service internally.

The load balancer source range check feature is enabled by default, and it can be disabled by setting config.svcSourceRangeCheck=false. It makes sense to disable the check when running on some cloud providers. E.g. Amazon NLB natively implements the check, so the kube-proxy replacement’s feature can be disabled. Meanwhile GKE internal TCP/UDP load balancer does not, so the feature must be kept enabled in order to restrict the access.

Service Proxy Name Configuration

Like kube-proxy, Cilium also honors the service.kubernetes.io/service-proxy-name service annotation and only manages services that contain a matching service-proxy-name label. This name can be configured by setting global.k8s.serviceProxyName option and the behavior is identical to that of kube-proxy. The service proxy name defaults to an empty string which instructs Cilium to only manage services not having service.kubernetes.io/service-proxy-name label.

For more details on the usage of service.kubernetes.io/service-proxy-name label and its working, take a look at this KEP.

Note

If Cilium with a non-empty service proxy name is meant to manage all services in kube-proxy free mode, make sure that default Kubernetes services like kube-dns and kubernetes have the required label value.

Limitations

  • Cilium’s BPF kube-proxy replacement currently cannot be used with Transparent Encryption (stable/beta).
  • Cilium’s BPF kube-proxy replacement relies upon the Host-Reachable Services feature which uses BPF cgroup hooks to implement the service translation. The getpeername(2) hook address translation in BPF is only available for v5.8 kernels. It is known to currently not work with libceph deployments.
  • Cilium’s BPF kube-proxy acceleration in XDP can only be used in a single device setup as a “one-legged” / hairpin load balancer scenario. In case of a multi-device environment, where auto-detection selects more than a single device to expose NodePort, the option global.devices=eth0 must be specified in helm in order to work, where eth0 is the native XDP supported networking device.
  • Cilium’s DSR NodePort mode currently does not operate well in environments with TCP Fast Open (TFO) enabled. It is recommended to switch to snat mode in this situation.
  • Cilium’s BPF kube-proxy replacement does not support the SCTP transport protocol. Only TCP and UDP is supported as a transport for services at this point.
  • Cilium’s BPF kube-proxy replacement does not allow hostPort port configurations for Pods that overlap with the configured NodePort range. In such case, the hostPort setting will be ignored and a warning emitted to the Cilium agent log. Similarly, explicitly binding the hostIP to the loopback address in the host namespace is currently not supported and will log a warning to the Cilium agent log.
  • When Cilium’s kube-proxy replacement is used with Kubernetes versions(< 1.19) that have support for EndpointSlices, Services without selectors and backing Endpoints don’t work. The reason is that Cilium only monitors changes made to EndpointSlices objects if support is available and ignores Endpoints in those cases. Kubernetes 1.19 release introduces EndpointSliceMirroring controller that mirrors custom Endpoints resources to corresponding EndpointSlices and thus allowing backing Endpoints to work. For a more detailed discussion see #12438.
  • As per k8s Service, Cilium’s eBPF kube-proxy replacement disallow access of a ClusterIP service from outside a cluster.

Further Readings

The following presentations describe inner-workings of the kube-proxy replacement in BPF in great details:

  • “Liberating Kubernetes from kube-proxy and iptables” (KubeCon North America 2019, slides, video)
  • “BPF as a revolutionary technology for the container landscape” (Fosdem 2020, slides, video)
  • “Kernel improvements for Cilium socket LB” (LSF/MM/BPF 2020, slides)