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add blog for feature LoadBalancerIPMode
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...en/blog/_posts/2023-12-18-kubernetes-1-29-feature-loadbalancer-ip-mode-alpha.md
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| --- | ||
| layout: blog | ||
| title: "Kubernetes 1.29: New (alpha) Feature, Load Balancer IP Mode for Services" | ||
| date: 2023-12-18 | ||
| slug: kubernetes-1-29-feature-loadbalancer-ip-mode-alpha | ||
| --- | ||
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| **Author:** [Aohan Yang](https://github.com/RyanAoh) | ||
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| This blog introduces a new alpha feature in Kubernetes 1.29. | ||
| It provides a configurable approach to define how Service implementations, | ||
| exemplified in this blog by kube-proxy, | ||
| handle traffic from pods to the Service, within the cluster. | ||
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| ## Background | ||
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| In older Kubernetes releases, the kube-proxy would intercept traffic that was destined for the IP | ||
| address associated with a Service of `type: LoadBalancer`. This happened whatever mode you used | ||
| for `kube-proxy`. | ||
| The interception implemented the expected behavior (traffic eventually reaching the expected | ||
| endpoints behind the Service). The mechanism to make that work depended on the mode for kube-proxy; | ||
| on Linux, kube-proxy in iptables mode would redirecting packets directly to the endpoint; in ipvs mode, | ||
| kube-proxy would configure the load balancer's IP address to one interface on the node. | ||
| The motivation for implementing that interception was for two reasons: | ||
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| 1. **Traffic path optimization:** Efficiently redirecting pod traffic - when a container in a pod sends an outbound | ||
| packet that is destined for the load balancer's IP address - | ||
| directly to the backend service by bypassing the load balancer. | ||
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| 2. **Handling load balancer packets:** Some load balancers send packets with the destination IP set to | ||
| the load balancer's IP address. As a result, these packets need to be routed directly to the correct backend (which | ||
| might not be local to that node), in order to avoid loops. | ||
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| ## Problems | ||
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| However, there are several problems with the aforementioned behavior: | ||
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| 1. **[Source IP](https://github.com/kubernetes/kubernetes/issues/79783):** | ||
| Some cloud providers use the load balancer's IP as the source IP when | ||
| transmitting packets to the node. In the ipvs mode of kube-proxy, | ||
| there is a problem that health checks from the load balancer never return. This occurs because the reply packets | ||
| would be forward to the local interface `kube-ipvs0`(where the load balancer's IP is bound to) | ||
| and be subsequently ignored. | ||
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| 2. **[Feature loss at load balancer level](https://github.com/kubernetes/kubernetes/issues/66607):** | ||
| Certain cloud providers offer features(such as TLS termination, proxy protocol, etc.) at the | ||
| load balancer level. | ||
| Bypassing the load balancer results in the loss of these features when the packet reaches the service | ||
| (leading to protocol errors). | ||
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| Even with the new alpha behaviour disabled (the default), there is a | ||
| [workaround](https://github.com/kubernetes/kubernetes/issues/66607#issuecomment-474513060) | ||
| that involves setting `.status.loadBalancer.ingress.hostname` for the Service, in order | ||
| to bypass kube-proxy binding. | ||
| But this is just a makeshift solution. | ||
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| ## Solution | ||
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| In summary, providing an option for cloud providers to disable the current behavior would be highly beneficial. | ||
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| To address this, Kubernetes v1.29 introduces a new (alpha) `.status.loadBalancer.ingress.ipMode` | ||
| field for a Service. | ||
| This field specifies how the load balancer IP behaves and can be specified only when | ||
| the `.status.loadBalancer.ingress.ip` field is also specified. | ||
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| Two values are possible for `.status.loadBalancer.ingress.ipMode`: `"VIP"` and `"Proxy"`. | ||
| The default value is "VIP", meaning that traffic delivered to the node | ||
| with the destination set to the load balancer's IP and port will be redirected to the backend service by kube-proxy. | ||
| This preserves the existing behavior of kube-proxy. | ||
| The "Proxy" value is intended to prevent kube-proxy from binding the load balancer's IP address | ||
| to the node in both ipvs and iptables modes. | ||
| Consequently, traffic is sent directly to the load balancer and then forwarded to the destination node. | ||
| The destination setting for forwarded packets varies depending on how the cloud provider's load balancer delivers traffic: | ||
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| - If the traffic is delivered to the node then DNATed to the pod, the destination would be set to the node's IP and node port; | ||
| - If the traffic is delivered directly to the pod, the destination would be set to the pod's IP and port. | ||
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| ## Usage | ||
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| Here are the necessary steps to enable this feature: | ||
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| - Download the [latest Kubernetes project](https://kubernetes.io/releases/download/) (version `v1.29.0` or later). | ||
| - Enable the feature gate with the command line flag `--feature-gates=LoadBalancerIPMode=true` | ||
| on kube-proxy, kube-apiserver, and cloud-controller-manager. | ||
| - For Services with `type: LoadBalancer`, set `ipMode` to the appropriate value. | ||
| This step is likely handled by your chosen cloud-controller-manager during the `EnsureLoadBalancer` process. | ||
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| ## More information | ||
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| - Read [Specifying IPMode of load balancer status](/docs/concepts/services-networking/service/#load-balancer-ip-mode). | ||
| - Read [KEP-1860](https://kep.k8s.io/1860) - [Make Kubernetes aware of the LoadBalancer behaviour](https://github.com/kubernetes/enhancements/tree/b103a6b0992439f996be4314caf3bf7b75652366/keps/sig-network/1860-kube-proxy-IP-node-binding#kep-1860-make-kubernetes-aware-of-the-loadbalancer-behaviour) _(sic)_. | ||
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| ## Getting involved | ||
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| Reach us on [Slack](https://slack.k8s.io/): [#sig-network](https://kubernetes.slack.com/messages/sig-network), | ||
| or through the [mailing list](https://groups.google.com/forum/#!forum/kubernetes-sig-network). | ||
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| ## Acknowledgments | ||
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| Huge thanks to [@Sh4d1](https://github.com/Sh4d1) for the original KEP and initial implementation code. | ||
| I took over midway and completed the work. Similarly, immense gratitude to other contributors | ||
| who have assisted in the design, implementation, and review of this feature (alphabetical order): | ||
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| - [@aojea](https://github.com/aojea) | ||
| - [@danwinship](https://github.com/danwinship) | ||
| - [@sftim](https://github.com/sftim) | ||
| - [@tengqm](https://github.com/tengqm) | ||
| - [@thockin](https://github.com/thockin) | ||
| - [@wojtek-t](https://github.com/wojtek-t) |