--- title: Using Source IP content_template: templates/tutorial --- {{% capture overview %}} Applications running in a Kubernetes cluster find and communicate with each other, and the outside world, through the Service abstraction. This document explains what happens to the source IP of packets sent to different types of Services, and how you can toggle this behavior according to your needs. {{% /capture %}} {{% capture prerequisites %}} {{< include "task-tutorial-prereqs.md" >}} {{< version-check >}} ## Terminology This document makes use of the following terms: * [NAT](https://en.wikipedia.org/wiki/Network_address_translation): network address translation * [Source NAT](https://en.wikipedia.org/wiki/Network_address_translation#SNAT): replacing the source IP on a packet, usually with a node's IP * [Destination NAT](https://en.wikipedia.org/wiki/Network_address_translation#DNAT): replacing the destination IP on a packet, usually with a pod IP * [VIP](/docs/concepts/services-networking/service/#virtual-ips-and-service-proxies): a virtual IP, such as the one assigned to every Kubernetes Service * [Kube-proxy](/docs/concepts/services-networking/service/#virtual-ips-and-service-proxies): a network daemon that orchestrates Service VIP management on every node ## Prerequisites You must have a working Kubernetes 1.5 cluster to run the examples in this document. The examples use a small nginx webserver that echoes back the source IP of requests it receives through an HTTP header. You can create it as follows: ```console $ kubectl run source-ip-app --image=k8s.gcr.io/echoserver:1.4 deployment "source-ip-app" created ``` {{% /capture %}} {{% capture objectives %}} * Expose a simple application through various types of Services * Understand how each Service type handles source IP NAT * Understand the tradeoffs involved in preserving source IP {{% /capture %}} {{% capture lessoncontent %}} ## Source IP for Services with Type=ClusterIP Packets sent to ClusterIP from within the cluster are never source NAT'd if you're running kube-proxy in [iptables mode](/docs/concepts/services-networking/service/#proxy-mode-iptables), which is the default since Kubernetes 1.2. Kube-proxy exposes its mode through a `proxyMode` endpoint: ```console $ kubectl get nodes NAME STATUS AGE VERSION kubernetes-minion-group-6jst Ready 2h v1.6.0+fff5156 kubernetes-minion-group-cx31 Ready 2h v1.6.0+fff5156 kubernetes-minion-group-jj1t Ready 2h v1.6.0+fff5156 kubernetes-minion-group-6jst $ curl localhost:10249/proxyMode iptables ``` You can test source IP preservation by creating a Service over the source IP app: ```console $ kubectl expose deployment source-ip-app --name=clusterip --port=80 --target-port=8080 service "clusterip" exposed $ kubectl get svc clusterip NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE clusterip 10.0.170.92 80/TCP 51s ``` And hitting the `ClusterIP` from a pod in the same cluster: ```console $ kubectl run busybox -it --image=busybox --restart=Never --rm Waiting for pod default/busybox to be running, status is Pending, pod ready: false If you don't see a command prompt, try pressing enter. # ip addr 1: lo: mtu 65536 qdisc noqueue link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet6 ::1/128 scope host valid_lft forever preferred_lft forever 3: eth0: mtu 1460 qdisc noqueue link/ether 0a:58:0a:f4:03:08 brd ff:ff:ff:ff:ff:ff inet 10.244.3.8/24 scope global eth0 valid_lft forever preferred_lft forever inet6 fe80::188a:84ff:feb0:26a5/64 scope link valid_lft forever preferred_lft forever # wget -qO - 10.0.170.92 CLIENT VALUES: client_address=10.244.3.8 command=GET ... ``` If the client pod and server pod are in the same node, the client_address is the client pod's IP address. However, if the client pod and server pod are in different nodes, the client_address is the client pod's node flannel IP address. ## Source IP for Services with Type=NodePort As of Kubernetes 1.5, packets sent to Services with [Type=NodePort](/docs/concepts/services-networking/service/#type-nodeport) are source NAT'd by default. You can test this by creating a `NodePort` Service: ```console $ kubectl expose deployment source-ip-app --name=nodeport --port=80 --target-port=8080 --type=NodePort service "nodeport" exposed $ NODEPORT=$(kubectl get -o jsonpath="{.spec.ports[0].nodePort}" services nodeport) $ NODES=$(kubectl get nodes -o jsonpath='{ $.items[*].status.addresses[?(@.type=="ExternalIP")].address }') ``` If you're running on a cloudprovider, you may need to open up a firewall-rule for the `nodes:nodeport` reported above. Now you can try reaching the Service from outside the cluster through the node port allocated above. ```console $ for node in $NODES; do curl -s $node:$NODEPORT | grep -i client_address; done client_address=10.180.1.1 client_address=10.240.0.5 client_address=10.240.0.3 ``` Note that these are not the correct client IPs, they're cluster internal IPs. This is what happens: * Client sends packet to `node2:nodePort` * `node2` replaces the source IP address (SNAT) in the packet with its own IP address * `node2` replaces the destination IP on the packet with the pod IP * packet is routed to node 1, and then to the endpoint * the pod's reply is routed back to node2 * the pod's reply is sent back to the client Visually: ``` client \ ^ \ \ v \ node 1 <--- node 2 | ^ SNAT | | ---> v | endpoint ``` To avoid this, Kubernetes has a feature to preserve the client source IP [(check here for feature availability)](/docs/tasks/access-application-cluster/create-external-load-balancer/#preserving-the-client-source-ip). Setting `service.spec.externalTrafficPolicy` to the value `Local` will only proxy requests to local endpoints, never forwarding traffic to other nodes and thereby preserving the original source IP address. If there are no local endpoints, packets sent to the node are dropped, so you can rely on the correct source-ip in any packet processing rules you might apply a packet that make it through to the endpoint. Set the `service.spec.externalTrafficPolicy` field as follows: ```console $ kubectl patch svc nodeport -p '{"spec":{"externalTrafficPolicy":"Local"}}' service "nodeport" patched ``` Now, re-run the test: ```console $ for node in $NODES; do curl --connect-timeout 1 -s $node:$NODEPORT | grep -i client_address; done client_address=104.132.1.79 ``` Note that you only got one reply, with the *right* client IP, from the one node on which the endpoint pod is running. This is what happens: * client sends packet to `node2:nodePort`, which doesn't have any endpoints * packet is dropped * client sends packet to `node1:nodePort`, which *does* have endpoints * node1 routes packet to endpoint with the correct source IP Visually: ``` client ^ / \ / / \ / v X node 1 node 2 ^ | | | | v endpoint ``` ## Source IP for Services with Type=LoadBalancer As of Kubernetes 1.5, packets sent to Services with [Type=LoadBalancer](/docs/concepts/services-networking/service/#type-loadbalancer) are source NAT'd by default, because all schedulable Kubernetes nodes in the `Ready` state are eligible for loadbalanced traffic. So if packets arrive at a node without an endpoint, the system proxies it to a node *with* an endpoint, replacing the source IP on the packet with the IP of the node (as described in the previous section). You can test this by exposing the source-ip-app through a loadbalancer ```console $ kubectl expose deployment source-ip-app --name=loadbalancer --port=80 --target-port=8080 --type=LoadBalancer service "loadbalancer" exposed $ kubectl get svc loadbalancer NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE loadbalancer 10.0.65.118 104.198.149.140 80/TCP 5m $ curl 104.198.149.140 CLIENT VALUES: client_address=10.240.0.5 ... ``` However, if you're running on Google Kubernetes Engine/GCE, setting the same `service.spec.externalTrafficPolicy` field to `Local` forces nodes *without* Service endpoints to remove themselves from the list of nodes eligible for loadbalanced traffic by deliberately failing health checks. Visually: ``` client | lb VIP / ^ v / health check ---> node 1 node 2 <--- health check 200 <--- ^ | ---> 500 | V endpoint ``` You can test this by setting the annotation: ```console $ kubectl patch svc loadbalancer -p '{"spec":{"externalTrafficPolicy":"Local"}}' ``` You should immediately see the `service.spec.healthCheckNodePort` field allocated by Kubernetes: ```console $ kubectl get svc loadbalancer -o yaml | grep -i healthCheckNodePort healthCheckNodePort: 32122 ``` The `service.spec.healthCheckNodePort` field points to a port on every node serving the health check at `/healthz`. You can test this: ``` $ kubectl get pod -o wide -l run=source-ip-app NAME READY STATUS RESTARTS AGE IP NODE source-ip-app-826191075-qehz4 1/1 Running 0 20h 10.180.1.136 kubernetes-minion-group-6jst kubernetes-minion-group-6jst $ curl localhost:32122/healthz 1 Service Endpoints found kubernetes-minion-group-jj1t $ curl localhost:32122/healthz No Service Endpoints Found ``` A service controller running on the master is responsible for allocating the cloud loadbalancer, and when it does so, it also allocates HTTP health checks pointing to this port/path on each node. Wait about 10 seconds for the 2 nodes without endpoints to fail health checks, then curl the lb ip: ```console $ curl 104.198.149.140 CLIENT VALUES: client_address=104.132.1.79 ... ``` __Cross platform support__ As of Kubernetes 1.5, support for source IP preservation through Services with Type=LoadBalancer is only implemented in a subset of cloudproviders (GCP and Azure). The cloudprovider you're running on might fulfill the request for a loadbalancer in a few different ways: 1. With a proxy that terminates the client connection and opens a new connection to your nodes/endpoints. In such cases the source IP will always be that of the cloud LB, not that of the client. 2. With a packet forwarder, such that requests from the client sent to the loadbalancer VIP end up at the node with the source IP of the client, not an intermediate proxy. Loadbalancers in the first category must use an agreed upon protocol between the loadbalancer and backend to communicate the true client IP such as the HTTP [X-FORWARDED-FOR](https://en.wikipedia.org/wiki/X-Forwarded-For) header, or the [proxy protocol](http://www.haproxy.org/download/1.5/doc/proxy-protocol.txt). Loadbalancers in the second category can leverage the feature described above by simply creating an HTTP health check pointing at the port stored in the `service.spec.healthCheckNodePort` field on the Service. {{% /capture %}} {{% capture cleanup %}} Delete the Services: ```console $ kubectl delete svc -l run=source-ip-app ``` Delete the Deployment, ReplicaSet and Pod: ```console $ kubectl delete deployment source-ip-app ``` {{% /capture %}} {{% capture whatsnext %}} * Learn more about [connecting applications via services](/docs/concepts/services-networking/connect-applications-service/) * Learn more about [loadbalancing](/docs/user-guide/load-balancer) {{% /capture %}}