Bandwidth Manager

This guide explains how to configure Cilium’s bandwidth manager to optimize TCP and UDP workloads and efficiently rate limit individual Pods if needed through the help of EDT (Earliest Departure Time) and eBPF. Cilium’s bandwidth manager is also prerequisite for enabling BBR congestion control for Pods as outlined below.

The bandwidth manager does not rely on CNI chaining and is natively integrated into Cilium instead. Hence, it does not make use of the bandwidth CNI plugin. Due to scalability concerns in particular for multi-queue network interfaces, it is not recommended to use the bandwidth CNI plugin which is based on TBF (Token Bucket Filter) instead of EDT.

Cilium’s bandwidth manager supports the kubernetes.io/egress-bandwidth Pod annotation which is enforced on egress at the native host networking devices. The bandwidth enforcement is supported for direct routing as well as tunneling mode in Cilium.

The kubernetes.io/ingress-bandwidth annotation is not supported and also not recommended to use. Limiting bandwidth happens natively at the egress point of networking devices in order to reduce or pace bandwidth usage on the wire. Enforcing at ingress would add yet another layer of buffer queueing right in the critical fast-path of a node via ifb device where ingress traffic first needs to be redirected to the ifb’s egress point in order to perform shaping before traffic can go up the stack. At this point traffic has already occupied the bandwidth usage on the wire, and the node has already spent resources on processing the packet. kubernetes.io/ingress-bandwidth annotation is ignored by Cilium’s bandwidth manager.

Note

Bandwidth Manager requires a v5.1.x or more recent Linux kernel.

Note

Make sure you have Helm 3 installed. Helm 2 is no longer supported.

Setup Helm repository:

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

Cilium’s bandwidth manager is disabled by default on new installations. To install Cilium with the bandwidth manager enabled, run

helm install cilium cilium/cilium --version 1.12.2 \
  --namespace kube-system \
  --set bandwidthManager.enabled=true

To enable the bandwidth manager on an existing installation, run

helm upgrade cilium cilium/cilium --version 1.12.2 \
  --namespace kube-system \
  --reuse-values \
  --set bandwidthManager.enabled=true
kubectl -n kube-system rollout restart ds/cilium

The native host networking devices are auto detected as 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 and manually specify the devices, set their names in the devices helm option (e.g. devices='{eth0,eth1,eth2}'). Each listed device has to be named the same on all Cilium-managed nodes.

Verify that the Cilium Pods have come up correctly:

$ kubectl -n kube-system get pods -l k8s-app=cilium
NAME                READY     STATUS    RESTARTS   AGE
cilium-crf7f        1/1       Running   0          10m
cilium-db21a        1/1       Running   0          10m

In order to verify whether the bandwidth manager feature has been enabled in Cilium, the cilium status CLI command provides visibility through the BandwidthManager info line. It also dumps a list of devices on which the egress bandwidth limitation is enforced:

$ kubectl -n kube-system exec ds/cilium -- cilium status | grep BandwidthManager
BandwidthManager:       EDT with BPF [BBR] [eth0]

To verify that egress bandwidth limits are indeed being enforced, one can deploy two netperf Pods in different nodes — one acting as a server and one acting as the client:

---
apiVersion: v1
kind: Pod
metadata:
  annotations:
    # Limits egress bandwidth to 10Mbit/s.
    kubernetes.io/egress-bandwidth: "10M"
  labels:
    # This pod will act as server.
    app.kubernetes.io/name: netperf-server
  name: netperf-server
spec:
  containers:
  - name: netperf
    image: cilium/netperf
    ports:
    - containerPort: 12865
---
apiVersion: v1
kind: Pod
metadata:
  # This Pod will act as client.
  name: netperf-client
spec:
  affinity:
    # Prevents the client from being scheduled to the
    # same node as the server.
    podAntiAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
      - labelSelector:
          matchExpressions:
          - key: app.kubernetes.io/name
            operator: In
            values:
            - netperf-server
        topologyKey: kubernetes.io/hostname
  containers:
  - name: netperf
    args:
    - sleep
    - infinity
    image: cilium/netperf

Once up and running, the netperf-client Pod can be used to test egress bandwidth enforcement on the netperf-server Pod. As the test streaming direction is from the netperf-server Pod towards the client, we need to check TCP_MAERTS:

$ NETPERF_SERVER_IP=$(kubectl get pod netperf-server -o jsonpath='{.status.podIP}')
$ kubectl exec netperf-client -- \
    netperf -t TCP_MAERTS -H "${NETPERF_SERVER_IP}"
MIGRATED TCP MAERTS TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.217.0.254 () port 0 AF_INET
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

 87380  16384  16384    10.00       9.56

As can be seen, egress traffic of the netperf-server Pod has been limited to 10Mbit per second.

In order to introspect current endpoint bandwidth settings from BPF side, the following command can be run (replace cilium-xxxxx with the name of the Cilium Pod that is co-located with the netperf-server Pod):

$ kubectl exec -it -n kube-system cilium-xxxxxx -- cilium bpf bandwidth list
IDENTITY   EGRESS BANDWIDTH (BitsPerSec)
491        10M

Each Pod is represented in Cilium as an Endpoint which has an identity. The above identity can then be correlated with the cilium endpoint list command.

Note

Bandwidth limits apply on a per-Pod scope. In our example, if multiple replicas of the Pod are created, then each of the Pod instances receives a 10M bandwidth limit.

BBR for Pods

The base infrastructure around MQ/FQ setup provided by Cilium’s bandwidth manager also allows for use of TCP BBR congestion control for Pods.

BBR is in particular suitable when Pods are exposed behind Kubernetes Services which face external clients from the Internet. BBR achieves higher bandwidths and lower latencies for Internet traffic, for example, it has been shown that BBR’s throughput can reach as much as 2,700x higher than today’s best loss-based congestion control and queueing delays can be 25x lower.

Note

BBR for Pods requires a v5.18.x or more recent Linux kernel.

To enable the bandwidth manager with BBR congestion control, deploy with the following:

helm upgrade cilium cilium/cilium --version 1.12.2 \
  --namespace kube-system \
  --reuse-values \
  --set bandwidthManager.enabled=true \
  --set bandwidthManager.bbr=true
kubectl -n kube-system rollout restart ds/cilium

In order for BBR to work reliably for Pods, it requires a 5.18 or higher kernel. As outlined in our Linux Plumbers 2021 talk, this is needed since older kernels do not retain timestamps of network packets when switching from Pod to host network namespace. Due to the latter, the kernel’s pacing infrastructure does not function properly in general (not specific to Cilium).

We helped with fixing this issue for recent kernels to retain timestamps and therefore to get BBR for Pods working. Prior to that kernel, BBR was only working for sockets which are in the initial network namespace (hostns). BBR also needs eBPF Host-Routing in order to retain the network packet’s socket association all the way until the packet hits the FQ queueing discipline on the physical device in the host namespace. (Without eBPF Host-Routing the packet’s socket association would otherwise be orphaned inside the host stacks forwarding/routing layer.)

In order to verify whether the bandwidth manager with BBR has been enabled in Cilium, the cilium status CLI command provides visibility again through the BandwidthManager info line:

$ kubectl -n kube-system exec ds/cilium -- cilium status | grep BandwidthManager
BandwidthManager:       EDT with BPF [BBR] [eth0]

Once this setting is enabled, it will use BBR as a default for all newly spawned Pods. Ideally, BBR is selected upon initial Cilium installation when the cluster is created such that all nodes and Pods in the cluster homogeneously use BBR as otherwise there could be potential unfairness issues for other connections still using CUBIC. Also note that due to the nature of BBR’s probing you might observe a higher rate of TCP retransmissions compared to CUBIC.

We recommend to use BBR in particular for clusters where Pods are exposed as Services which serve external clients connecting from the Internet.

Limitations

  • Bandwidth enforcement currently does not work in combination with L7 Cilium Network Policies. In case they select the Pod at egress, then the bandwidth enforcement will be disabled for those Pods.

  • Bandwidth enforcement doesn’t work with nested network namespace environments like Kind. This is because they typically don’t have access to the global sysctl under /proc/sys/net/core and the bandwidth enforcement depends on them.

Video

For more insights on Cilium’s bandwidth manager, check out this KubeCon talk on Better Bandwidth Management with eBPF.