Project: Antrea (Runtime / Cloud Native Network)
File: service-loadbalancer.md

<!-- toc --> - - - - - - - <!-- /toc --> In Kubernetes, implementing Services of type LoadBalancer usually requires an external load balancer. On cloud platforms (including public clouds and platforms like NSX-T) that support load balancers, Services of type LoadBalancer can be implemented by the Kubernetes Cloud Provider, which configures the cloud load balancers for the Services. However, the load balancer support is not available on all platforms, or in some cases, it is complex or has extra cost to deploy external load balancers. This document describes two options for supporting Services of type LoadBalancer with Antrea, without an external load balancer: Using Antrea's built-in external IP management for Services of type LoadBalancer Leveraging Antrea supports external IP management for Services of type LoadBalancer since version 1.5, which can work together with `AntreaProxy` or `kube-proxy` to implement Services of type LoadBalancer, without requiring an external load balancer. With the external IP management feature, Antrea can allocate an external IP for a Service of type LoadBalancer from an , and select a Node based on the ExternalIPPool's NodeSelector to host the external IP. Antrea configures the Service's external IP on the selected Node, and thus Service requests to the external IP will get to the Node, and they are then handled by `AntreaProxy` or `kube-proxy` on the Node and distributed to the Service's Endpoints. Antrea also implements a Node failover mechanism for Service external IPs. When Antrea detects a Node hosting an external IP is down, it will move the external IP to another available Node of the ExternalIPPool. If you are using `kube-proxy` in IPVS mode, you need to make sure `strictARP` is enabled in the `kube-proxy` configuration. For more information about how to configure `kube-proxy`, please refer to the [Interoperability with kube-proxy IPVS mode](#interoperability-with-kube-proxy-ipvs-mode) section. If you are using `kube-proxy` iptables mode or , no extra configuration change is needed. At this moment, external IP management for Services is an alpha feature of Antrea. The `ServiceExternalIP` feature gate of `antrea-agent` and `antrea-controller` must be enabled for the feature to work. You can enable the `ServiceExternalIP` feature gate in the `antrea-config` ConfigMap in the Antrea deployment YAML: ```yaml apiVersion: v1 kind: ConfigMap metadata: name: antrea-config namespace: kube-system data: antrea-agent.conf: | featureGates: ServiceExternalIP: true antrea-controller.conf: | featureGates: ServiceExternalIP: true ``` The feature works with both `AntreaProxy` and `kube-proxy`, including the following configurations: `AntreaProxy` without `proxyAll` enabled - this is `antrea-agent`'s default configuration, in which `kube-proxy` serves the request traffic for Services of type LoadBalancer (while `AntreaProxy` handles Service requests from Pods). `AntreaProxy` with `proxyAll` enabled - in this case, `AntreaProxy` handles all Service traffic, including Services of type LoadBalancer. `AntreaProxy` disabled - `kube-proxy` handles all Service traffic, including Services of type LoadBalancer. Service external IPs are allocated from an ExternalIPPool, which defines a pool of external IPs and the set of Nodes to which the external IPs can be assigned. To learn more information about ExternalIPPool, please refer to [the Egress documentation](egress.md#the-externalippool-resource). The example below defines an ExternalIPPool with IP range "10.10.0.2 -

and it selects the Nodes with label "network-role: ingress-node" to host the external IPs: ```yaml apiVersion: crd.antrea.io/v1beta1 kind: ExternalIPPool metadata: name: service-external-ip-pool spec: ipRanges: start: 10.10.0.2 end: 10.10.0.10 nodeSelector: matchLabels: network-role: ingress-node ``` For Antrea to manage the externalIP for a Service of type LoadBalancer, the Service should be annotated with `service.antrea.io/external-ip-pool`. For example: ```yaml apiVersion: v1 kind: Service metadata: name: my-service annotations: service.antrea.io/external-ip-pool: "service-external-ip-pool" spec: selector: app: MyApp ports: protocol: TCP port: 80 targetPort: 9376 type: LoadBalancer ``` You can also request a particular IP from an ExternalIPPool by setting the loadBalancerIP field in the Service spec to that specific IP available in the ExternalIPPool, Antrea will allocate the IP from the ExternalIPPool for the Service. For example: ```yaml apiVersion: v1 kind: Service metadata: name: my-service annotations: service.antrea.io/external-ip-pool: "service-external-ip-pool" spec: selector: app: MyApp loadBalancerIP: "10.10.0.2" ports: protocol: TCP port: 80 targetPort: 9376 type: LoadBalancer ``` Once Antrea allocates an external IP for a Service of type LoadBalancer, it will set the IP to the `loadBalancer.ingress` field in the Service resource `status`. For example: ```yaml apiVersion: v1 kind: Service metadata: name: my-service annotations: service.antrea.io/external-ip-pool: "service-external-ip-pool" spec: selector: app: MyApp ports: protocol: TCP port: 80 targetPort: 9376 clusterIP: 10.96.0.11 type: LoadBalancer status: loadBalancer: ingress: ip: 10.10.0.2 hostname: node-1 ``` You can validate that the Service can be accessed from the client using the `<external IP>:<port>` (`10.10.0.2:80/TCP` in the above example). As described above, the Service externalIP management by Antrea configures a Service's external IP to a Node, so that the Node can receive Service requests. However, this requires that the externalIP on the Node be reachable through the Node network. The simplest way to achieve this is to reserve a range of IPs from the Node network subnet, and define Service ExternalIPPools with the reserved IPs, when the Nodes are connected to a layer 2 subnet. Or, another possible way might be to manually configure Node network routing (e.g. by adding a static route entry to the underlay router) to route the Service traffic to the Node that hosts the Service's externalIP. As of now, Antrea supports Service externalIP management only on Linux Nodes. Windows Nodes are not supported yet. MetalLB also implements external IP management for Services of type LoadBalancer, and it can be deployed to a Kubernetes cluster with Antrea. MetalLB supports two modes - layer 2 mode and BGP mode - to advertise an Service external IP to the Node network. The layer 2 mode is similar to what Antrea external IP management implements and has the same limitation that the external IPs must be allocated from the Node network subnet. The BGP mode leverages BGP to advertise external IPs to the Node network router. It does not have the layer 2 subnet limitation, but requires the Node network to support BGP. MetalLB will automatically allocate external IPs for every Service of type LoadBalancer, and it sets the allocated IP to the `loadBalancer.ingress` field in the Service resource `status`. MetalLB also supports user specified `loadBalancerIP` in the Service spec. For more information, please refer to the . To learn more about MetalLB concepts and functionalities, you can read the

You can run the following commands to install MetalLB using the YAML manifests: ```bash kubectl apply -f https://raw.githubusercontent.com/metallb/metallb/v0.13.11/config/manifests/metallb-native.yaml ``` The commands will deploy MetalLB version 0.13.11 into Namespace `metallb-system`. You can also refer to this [MetalLB installation guide](https://metallb.universe.tf/installation) for other ways of installing MetalLB. As MetalLB will allocate external IPs for all Services of type LoadBalancer, once it is running, the Service external IP management feature of Antrea should not be enabled to avoid conflicts with MetalLB. You can deploy Antrea with the default configuration (in which the `ServiceExternalIP` feature gate of `antrea-agent` is set to `false`). MetalLB can work with both `AntreaProxy` and `kube-proxy` configurations of `antrea-agent`. Similar to the case of Antrea Service external IP management, MetalLB layer 2 mode also requires `kube-proxy`'s `strictARP` configuration to be enabled, when you are using `kube-proxy` IPVS. Please refer to the [Interoperability with kube-proxy IPVS mode](#interoperability-with-kube-proxy-ipvs-mode) section for more information. MetalLB is configured through Custom Resources (since v0.13). To configure MetalLB to work in the layer 2 mode, you need to create an `L2Advertisement` resource, as well as an `IPAddressPool` resource, which provides the IP ranges to allocate external IPs from. The IP ranges should be from the Node network subnet. For example: ```yaml apiVersion: metallb.io/v1beta1 kind: IPAddressPool metadata: name: first-pool namespace: metallb-system spec: addresses: 10.10.0.2-10.10.0.10 apiVersion: metallb.io/v1beta1 kind: L2Advertisement metadata: name: example namespace: metallb-system ``` The BGP mode of MetalLB requires more configuration parameters to establish BGP peering to the router. The example resources below configure MetalLB using AS number 64500 to connect to peer router 10.0.0.1 with AS number 64501: ```yaml apiVersion: metallb.io/v1beta2 kind: BGPPeer metadata: name: sample namespace: metallb-system spec: myASN: 64500 peerASN: 64501 peerAddress: 10.0.0.1 apiVersion: metallb.io/v1beta1 kind: IPAddressPool metadata: name: first-pool namespace: metallb-system spec: addresses: 10.10.0.2-10.10.0.10 apiVersion: metallb.io/v1beta1 kind: BGPAdvertisement metadata: name: example namespace: metallb-system ``` In addition to the basic layer 2 and BGP mode configurations described in this document, MetalLB supports a few more advanced BGP configurations and supports configuring multiple IP pools which can use different modes. For more information, please refer to the . Both Antrea Service external IP management and MetalLB layer 2 mode require `kube-proxy`'s `strictARP` configuration to be enabled, to work with `kube-proxy` in IPVS mode. You can check the `strictARP` configuration in the `kube-proxy` ConfigMap: ```bash $ kubectl describe configmap -n kube-system kube-proxy | grep strictARP strictARP: false ``` You can set `strictARP` to `true` by editing the `kube-proxy` ConfigMap: ```bash kubectl edit configmap -n kube-system kube-proxy ``` Or, simply run the following command to set it: ```bash $ kubectl get configmap kube-proxy -n kube-system -o yaml | \ sed -e "s/strictARP: false/strictARP: true/" | \ kubectl apply -f - -n kube-system ``` Last, to check the change is made: ```bash $ kubectl describe configmap -n kube-system kube-proxy | grep strictARP strictARP: true ``` If you are using Antrea v1.7.0 or later, please ignore the issue. The previous implementation of Antrea Egress before v1.7.0 does not work with the `strictARP` configuration of `kube-proxy`. It means Antrea Egress cannot work together with Service external IP management or MetalLB layer 2 mode, when `kube-proxy` IPVS is used. This issue was fixed in Antrea v1.7.0.