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| Author | SHA1 | Date | |
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  claude-botandClaude Opus 5
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f0701370db | ||
 k.renner
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9131f73d6c | ||
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claude-botandClaude Opus 5
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k.renner
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41556cbb16 |
@@ -0,0 +1,117 @@
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# Traffic classes on the k8s nodes
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Issue #576. Three of the four classes are separated; management is not.
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## Where each class runs
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| class | link | mechanism |
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|---|---|---|
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| Ceph replication | `ceph-san`, VLAN 49 | the whole link is handed to the OSD pod (Multus `host-device`) |
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| world→pod | `ingress0`, VLAN 47 | BGP session sourced there, so the advertised next hop is that address |
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| pod→world | `ingress0`, VLAN 47 | routing rule on the pod source prefix → table 47 |
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| pod↔pod | `pod0`, VLAN 48 | routing rule on pod source **and** destination → table 48 |
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| management | `mgmt0`, VLAN 40 | not started |
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Hard constraint, set by the owner: inter-node and pod traffic never traverses
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the UDM. Everything above stays on the 10G switch.
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## Why policy routing rather than moving the node IP
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Cilium reaches a peer's pods at that peer's Kubernetes InternalIP, in native
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and tunnel mode alike. `--ipv4-node` is overwritten from the Node object, and
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`nodePort.directRoutingDevice` selects the BPF NodePort device, not a next hop.
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Both were established by test (#837, #838), not by reading.
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So the InternalIP decides where pod traffic goes — unless the lookup happens in
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a different table. The rules do that, and nothing about the node's identity
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moves. The routing decision runs before Cilium's masquerade hook, so a rule
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matching the pod source sees the pod address, and the masquerade then rewrites
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it to the egress link's.
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## Rule order
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Lower priority runs first.
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| prio | match | table |
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|---|---|---|
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| 980 | src pod, dst pod | 48 |
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| 981 | src pod, dst pod (v4) | 48 |
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| 990 | dst `fd00::/8` | main |
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| 991 | dst `10.0.0.0/8` | main |
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| 1000 | src pod | 47 |
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| 1001 | src pod (v4) | 47 |
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980/981 match source **and** destination. Source alone would also catch the
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node's own traffic to a pod, which would then leave with a `pod0` source — an
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address `CiliumNode.spec.addresses` does not list, so Cilium classifies it as
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`world` rather than `host`.
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990/991 are Cilium's `ipv4/ipv6NativeRoutingCIDR`, and they are what keeps
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cluster-internal traffic out of table 47. Without them a pod's packet to a
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service matches the source rule, finds only a default route, and leaves for the
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UDM — measured, in-cluster DNS stopped resolving.
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Traffic to a pod on the same node falls through on its own: table 48 holds only
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the peers' CIDRs, so the lookup misses and 990/991 send it to main.
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## Where each table comes from
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- **47** — two default routes declared per node in `talos/patches/k8s-*.yaml`.
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The IPv6 gateway is the UDM's configured address on the segment, not the
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RA-learned link-local; `accept_ra_defrtr` stays `0` on `ingress0` so the RA
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default does not land in main.
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- **48** — filled by the `bird` DaemonSet: an iBGP mesh over `pod0`, one route
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per peer pod CIDR with the peer's `pod0` address as next hop.
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## The bird mesh
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`kubernetes/infrastructure/bird/`. Each node advertises only its own pod CIDR
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and installs what it learns into table 48. Cilium's routes in main are
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untouched, which is why the two coexist.
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No address is written into this repo twice. Each node publishes its `pod0`
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addresses as `nodeAnnotations`, beside the `VLANConfig` that assigns them; the
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pod CIDRs come from the Node objects. An init container renders both from the
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API with `kubectl -o go-template-file`, excludes the node itself with a field
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selector, and ends with `bird -p` so BIRD's own parser gates startup.
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The node's own CIDR is **originated**, not read back from the kernel. Reading
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it back made BIRD depend on the shape Cilium installs, and the IPv4 route is
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rejected outright: its next hop sits inside the prefix it describes, which KRT
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refuses with `strange next-hop`. The IPv6 route is a device route and passed,
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so the failure was silent on one family only.
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## Failure behaviour
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Benign at every layer. An empty or absent table 48 makes 980/981 fall through
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to main, and pod traffic returns to VLAN 40 — unseparated, not broken. The same
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holds if the DaemonSet cannot start, which is the case during a cold rebuild
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until Gitea serves its image.
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## Management, the remaining class
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Not started. The levers differ per service and none of them is the node IP:
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| service | can leave the node IP? | lever |
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|---|---|---|
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| etcd | yes | `cluster.etcd.advertisedSubnets`; needs a reboot per node |
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| kube-apiserver endpoint | yes | it is a VIP — `Layer2VIPConfig.link` |
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| Talos API | n/a | `apid` answers on every node address; a firewall question |
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| kubelet | no | it *is* the node IP |
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Two approaches were rejected by the owner and are not to be proposed again:
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moving the node IP and etcd to `pod0` (#838), and relabelling VLAN 40 as the
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cluster VLAN while moving etcd and the API VIP to a new management VLAN.
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Replacing the CNI (#839, Antrea) was shelved.
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Note that the reasoning which produced that list also concluded pod↔pod was
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blocked, which policy routing disproved. Treat it as a record of decisions, not
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as an exhaustive analysis.
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## Sources
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Cilium v1.20.1 `pkg/datapath/linux/node.go`, `pkg/node/types/node.go`,
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`pkg/node/sync/local_node_sync.go`; BIRD 2.17 user manual (kernel protocol,
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`learn all`, `strict bind`, `direct`); Talos v1.13 `RoutingRuleConfig` and
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`machine.nodeAnnotations`. PRs #831, #833, #835, #836, #837, #842, #852, #854,
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#855; closed unmerged: #830, #838, #839.
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@@ -1,194 +0,0 @@
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# Proposal — separate the four traffic classes onto their own VLANs
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Status: draft. The question this started with is **answered** — from the Cilium
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source and flag reference, not from a test — and the answer changes the shape
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of the proposal rather than confirming it.
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Supersedes the framing in issue #576, which described this as "give node
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management its own NIC, and Ceph public its own VLAN". That was two of four
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classes and one of them turned out already solved.
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## The four classes
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| class | what it is | where it goes today |
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|---|---|---|
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| **Ceph replication** | OSD-to-OSD heartbeat, replication, recovery | VLAN 49, its own X710 port — **separated** |
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| **cluster-internal** | pod-to-pod east-west, including Ceph client I/O | pod network, VXLAN over `mgmt0` |
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| **cluster-external** | ingress to LoadBalancer VIPs, egress to LAN and internet | `mgmt0` |
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| **management** | Talos API, etcd, kube-apiserver, kubelet | `mgmt0` |
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Three of four share one interface. That is not a design decision — until the
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bare-metal conversion there was one NIC to work with.
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Ceph client I/O living on the pod network is correct rather than a leftover:
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that traffic *is* cluster-internal. Ceph is done.
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## Principle
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**Each class gets its own VLAN. Which physical interface a VLAN lands on is a
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separate, changeable decision.**
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Defining classes by VLAN means the separation survives recabling, port failures
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and capacity changes, and it does not require one port per class. Defining them
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by interface would freeze a capacity decision into the architecture.
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## The finding that shapes everything else
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The original open question was whether `nodePort.directRoutingDevice` moves the
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next-hop of Cilium's direct routes, or only selects an interface. It is
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answerable from the source, and the answer is: **only the interface.**
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`installDirectRoute` takes the next-hop as a parameter:
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```go
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func installDirectRoute(log *slog.Logger, prefix netip.Prefix, nodeIP net.IP,
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skipUnreachable bool) (routeSpec *netlink.Route, err error)
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```
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and `nodeUpdate` supplies it as `newNode.GetNodeIP(false)`. `GetNodeIP` returns,
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in priority order, `NodeInternalIP` → `NodeExternalIP` → anything else. The
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same `newIP4` is what tunnel mode uses as the VXLAN endpoint.
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`NodeInternalIP` comes from the Kubernetes Node object. `--ipv4-node` looks like
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an override but is not one: `initFromConfig()` calls `SetNodeInternalIP` and
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`initFromK8s()` runs **after** it and overwrites the value. In a Kubernetes
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cluster there is no path by which Cilium's node IP differs from the kubelet's
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`InternalIP`.
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`--direct-routing-device` is documented as "Device name used to connect nodes in
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direct routing mode" — a device, not an address.
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**So cluster-internal traffic is welded to the node IP, and the node IP is the
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kubelet InternalIP.** Two consequences:
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- The class cannot be moved off whatever VLAN the node IP lives on.
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- **Routing mode is irrelevant to this problem.** Tunnel mode sources the VXLAN
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from the node IP; native mode uses it as the direct-route next-hop. Native
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routing buys nothing here, so the disruptive, non-rolling step this proposal
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previously contained is simply gone.
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## Consequence: draw the line the other way
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If cluster-internal cannot leave the node IP, then separation has to come from
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moving *management services* off it — and each one has to be checked
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individually, because they do not share a mechanism.
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| management service | can it leave the node IP? | lever |
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|---|---|---|
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| etcd | **yes** | `cluster.etcd.advertisedSubnets` (+ `listenSubnets`, which defaults to it) |
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| kube-apiserver endpoint | **yes** | already a VIP — `Layer2VIPConfig` with a `link:` field |
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| Talos API | **n/a** | `apid` answers on every node address (measured); a client and firewall choice, not a bind setting |
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| kubelet | **no** | it *is* the node IP, by definition |
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So four VLANs are reachable, but the boundary does not fall where the class
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names suggest: **kubelet stays with cluster-internal.** That is the honest
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result, and it is worth stating plainly rather than filing kubelet under
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management and hoping.
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The remaining classes keep the levers established earlier:
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- **cluster-external ingress** — `CiliumBGPNodeConfigOverride.spec.bgpInstances[].peers[].localAddress`.
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For eBGP the session source is the next-hop, so pinning the session pins
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where return traffic arrives. The session to the UDM has been running for
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months.
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- **cluster-external egress** — eBPF masquerading follows the output device, so
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this is a default-route decision plus `enable-masquerade-to-route-source`
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(today `false`).
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- **Ceph replication** — Multus macvlan on VLAN 49, done.
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## The general escape hatch
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Ceph is separated because its OSDs got a second interface and stopped using the
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pod network for replication. That is the *only* mechanism that fully detaches a
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workload from the node IP, and it generalises: anything that must not ride the
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node IP gets its own `NetworkAttachmentDefinition`.
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It is also expensive per workload — an attachment, an IPAM pool, a pod spec
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change. Worth it for Ceph replication. Not worth it for east-west traffic in
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general.
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## Recommended mapping
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Two ways to arrange this, and they differ only in which VLAN gets relabelled:
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**A — move the node IP to a new cluster VLAN.** VLAN 40 keeps etcd, the API VIP
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and Talos API. Cleanest match to the class names, but it changes every node's
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identity, which is the one address the whole cluster is administered through.
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**B (recommended) — leave the node IP on VLAN 40 and move management off it.**
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VLAN 40 becomes the cluster VLAN; a new VLAN carries etcd and the API VIP.
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Identical end state, and no node ever changes its InternalIP.
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Under B:
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| VLAN | carries |
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|---|---|
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| 49 | Ceph replication |
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| 40 (relabelled *cluster*) | pod east-west, kubelet |
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| new *management* | etcd, kube-apiserver VIP, Talos API by convention |
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| new *external* | LoadBalancer ingress, egress default route |
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The property the user asked for — management carries only management traffic —
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holds under B. The label moves; the property is what matters.
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## Migration shape
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Every step is rolling and reversible. The routing-mode change is gone.
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1. **New VLANs** on the switch, trunked to the X710. Nothing uses them.
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2. **Addresses** on the new VLANs via Talos, one node at a time, `--mode=try`.
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Still unused; this only proves the L2 works.
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3. **etcd** to the management VLAN via `advertisedSubnets`. One node at a time,
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waiting for a healthy quorum between each.
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4. **API VIP** to the management VLAN via `Layer2VIPConfig.link`. DNS for
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`k8s.renner.uno` follows.
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5. **cluster-external**: BGP `localAddress`, default route, masquerade flag.
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Reversible by reverting the override; failure is visible immediately in
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`cilium-dbg shell -- bgp/peers`.
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6. Verify VLAN 40 by what is *absent* from it, not by what still works.
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Step 3 is the one that deserves care — etcd is the only step where a mistake
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costs quorum rather than connectivity.
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## What this does not buy
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Management currently shares a 10 Gb link and is not contended. Nothing observed
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today is slow because of this. The case for the split is that traffic classes
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with different failure modes and security postures should not be
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indistinguishable — not that something is broken.
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## Sources and measurements
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Source, Cilium v1.20.1 (the running version):
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- `pkg/datapath/linux/node.go` — `installDirectRoute(…, nodeIP net.IP, …)`,
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fed from `newIP4 = newNode.GetNodeIP(false)`; `createDirectRouteSpec` rejects
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a next-hop that is not directly reachable.
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- `pkg/node/types/node.go` — `GetNodeIP` prefers `NodeInternalIP`.
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- `pkg/node/sync/local_node_sync.go` — `initFromConfig()` applies
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`--ipv4-node`, `initFromK8s()` runs afterwards and overwrites it from the
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Kubernetes Node.
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- `cilium-agent` flag reference — `--direct-routing-device`: "Device name used
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to connect nodes in direct routing mode".
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Talos:
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- Multihoming guide — `cluster.etcd.advertisedSubnets`; `listenSubnets`
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defaults to it. kube-apiserver and Talos API listen addresses are not
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covered there.
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- `kubernetes/talos/patches/k8s-{1,2,3}.yaml` — `Layer2VIPConfig` for
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`10.2.40.60` with `link: mgmt0`.
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Measured on the cluster:
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- `apid` answered on a node address that is not the InternalIP, so the Talos
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API is not bound to one address.
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- k8s-1 currently holds one routable v4 address plus the VIP on `mgmt0`; its
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InternalIP had changed since the last session, which is why nothing here
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names an address as fixed.
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- Cilium runs `routing-mode: tunnel` with `enable-masquerade-to-route-source`
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unset and no direct-routing device configured.
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Not verified: whether the kube-apiserver's `--advertise-address` follows the
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node IP independently of the VIP. It does not affect the recommendation, since
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clients reach the API through the VIP either way.
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@@ -610,8 +610,8 @@ if [[ "$PHASE" == "hcloudtest" ]]; then
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# Constraints on the choice: cpx11/cpx21 are US-only and cax* are ARM, which
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# would not match the amd64 schematic this cluster installs. That leaves the
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# cx*/cpx*2 families in the German locations.
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# Today's traffic-class split, not the target one in
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# PROPOSAL-traffic-class-separation.md: the node address carries management,
|
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# Two segments only, unlike the homelab's split in
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# NETWORK-traffic-classes.md: here the node address carries management,
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# cluster-internal and external alike, and Ceph replication has its own.
|
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#
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# The order is load-bearing: it decides which kernel interface each segment
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@@ -41,6 +41,29 @@ machine:
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# Priorities are below main (32766) and clear of the rule Cilium installs at 9.
|
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# The two families are separate rule tables, so the priorities need not match;
|
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# the document name is the priority and must be unique.
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# Pod to pod between nodes goes over pod0, via table 48, which the bird mesh
|
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# fills with one route per peer pod CIDR and the peer's pod0 address as the
|
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# next hop. Ahead of 990/991 so it wins for that traffic, and matching source
|
||||
# AND destination so nothing else lands there: the node's own traffic to a pod
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# would otherwise leave with a pod0 source, which CiliumNode does not list, so
|
||||
# Cilium would classify it as world rather than host.
|
||||
#
|
||||
# Traffic to a pod on this node falls through — table 48 holds only the peers'
|
||||
# CIDRs, so the lookup misses and 990/991 send it to main and cilium_host.
|
||||
apiVersion: v1alpha1
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kind: RoutingRuleConfig
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name: "980"
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src: fd10:244::/48
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dst: fd10:244::/48
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table: "48"
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---
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apiVersion: v1alpha1
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kind: RoutingRuleConfig
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name: "981"
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src: 10.244.0.0/16
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dst: 10.244.0.0/16
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table: "48"
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---
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apiVersion: v1alpha1
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kind: RoutingRuleConfig
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name: "990"
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|
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Reference in New Issue
Block a user