HA endpoints for K8s ==================== The following components require a highly available endpoints: * etcd cluster, * kube-apiserver service instances. The latter relies on a 3rd side reverse proxies, like Nginx or HAProxy, to achieve the same goal. Etcd ---- The `etcd_access_endpoint` fact provides an access pattern for clients. And the `etcd_multiaccess` (defaults to `True`) group var controls that behavior. It makes deployed components to access the etcd cluster members directly: `http://ip1:2379, http://ip2:2379,...`. This mode assumes the clients do a loadbalancing and handle HA for connections. Kube-apiserver -------------- K8s components require a loadbalancer to access the apiservers via a reverse proxy. Kubespray includes support for an nginx-based proxy that resides on each non-master Kubernetes node. This is referred to as localhost loadbalancing. It is less efficient than a dedicated load balancer because it creates extra health checks on the Kubernetes apiserver, but is more practical for scenarios where an external LB or virtual IP management is inconvenient. This option is configured by the variable `loadbalancer_apiserver_localhost` (defaults to `True`. Or `False`, if there is an external `loadbalancer_apiserver` defined). You may also define the port the local internal loadbalancer uses by changing, `nginx_kube_apiserver_port`. This defaults to the value of `kube_apiserver_port`. It is also important to note that Kubespray will only configure kubelet and kube-proxy on non-master nodes to use the local internal loadbalancer. If you choose to NOT use the local internal loadbalancer, you will need to configure your own loadbalancer to achieve HA. Note that deploying a loadbalancer is up to a user and is not covered by ansible roles in Kubespray. By default, it only configures a non-HA endpoint, which points to the `access_ip` or IP address of the first server node in the `kube-master` group. It can also configure clients to use endpoints for a given loadbalancer type. The following diagram shows how traffic to the apiserver is directed. ![Image](figures/loadbalancer_localhost.png?raw=true) Note: Kubernetes master nodes still use insecure localhost access because there are bugs in Kubernetes <1.5.0 in using TLS auth on master role services. This makes backends receiving unencrypted traffic and may be a security issue when interconnecting different nodes, or maybe not, if those belong to the isolated management network without external access. A user may opt to use an external loadbalancer (LB) instead. An external LB provides access for external clients, while the internal LB accepts client connections only to the localhost. Given a frontend `VIP` address and `IP1, IP2` addresses of backends, here is an example configuration for a HAProxy service acting as an external LB: ``` listen kubernetes-apiserver-https bind :8383 option ssl-hello-chk mode tcp timeout client 3h timeout server 3h server master1 :6443 server master2 :6443 balance roundrobin ``` Note: That's an example config managed elsewhere outside of Kubespray. And the corresponding example global vars for such a "cluster-aware" external LB with the cluster API access modes configured in Kubespray: ``` apiserver_loadbalancer_domain_name: "my-apiserver-lb.example.com" loadbalancer_apiserver: address: port: 8383 ``` Note: The default kubernetes apiserver configuration binds to all interfaces, so you will need to use a different port for the vip from that the API is listening on, or set the `kube_apiserver_bind_address` so that the API only listens on a specific interface (to avoid conflict with haproxy binding the port on the VIP adddress) This domain name, or default "lb-apiserver.kubernetes.local", will be inserted into the `/etc/hosts` file of all servers in the `k8s-cluster` group and wired into the generated self-signed TLS/SSL certificates as well. Note that the HAProxy service should as well be HA and requires a VIP management, which is out of scope of this doc. There is a special case for an internal and an externally configured (not with Kubespray) LB used simultaneously. Keep in mind that the cluster is not aware of such an external LB and you need no to specify any configuration variables for it. Note: TLS/SSL termination for externally accessed API endpoints' will **not** be covered by Kubespray for that case. Make sure your external LB provides it. Alternatively you may specify an externally load balanced VIPs in the `supplementary_addresses_in_ssl_keys` list. Then, kubespray will add them into the generated cluster certifactes as well. Aside of that specific case, the `loadbalancer_apiserver` considered mutually exclusive to `loadbalancer_apiserver_localhost`. Access API endpoints are evaluated automagically, as the following: | Endpoint type | kube-master | non-master | external | |------------------------------|----------------|---------------------|---------------------| | Local LB (default) | https://bip:sp | https://lc:nsp | https://m[0].aip:sp | | Local LB + Unmanaged here LB | https://bip:sp | https://lc:nsp | https://ext | | External LB, no internal | https://bip:sp | https://lb:lp | https://lb:lp | | No ext/int LB | https://bip:sp | https://m[0].aip:sp | https://m[0].aip:sp | Where: * `m[0]` - the first node in the `kube-master` group; * `lb` - LB FQDN, `apiserver_loadbalancer_domain_name`; * `ext` - Externally load balanced VIP:port and FQDN, not managed by Kubespray; * `lc` - localhost; * `bip` - a custom bind IP or localhost for the default bind IP '0.0.0.0'; * `nsp` - nginx secure port, `nginx_kube_apiserver_port`, defers to `sp`; * `sp` - secure port, `kube_apiserver_port`; * `lp` - LB port, `loadbalancer_apiserver.port`, defers to the secure port; * `ip` - the node IP, defers to the ansible IP; * `aip` - `access_ip`, defers to the ip. A second and a third column represent internal cluster access modes. The last column illustrates an example URI to access the cluster APIs externally. Kubespray has nothing to do with it, this is informational only. As you can see, the masters' internal API endpoints are always contacted via the local bind IP, which is `https://bip:sp`. **Note** that for some cases, like healthchecks of applications deployed by Kubespray, the masters' APIs are accessed via the insecure endpoint, which consists of the local `kube_apiserver_insecure_bind_address` and `kube_apiserver_insecure_port`.