dd82ed2a1f
Fix mismatch in code and docs, see https://github.com/kubespray/kargo/pull/528 Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>
109 lines
4.7 KiB
Markdown
109 lines
4.7 KiB
Markdown
HA endpoints for K8s
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====================
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The following components require a highly available endpoints:
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* etcd cluster,
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* kube-apiserver service instances.
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The former provides the
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[etcd-proxy](https://coreos.com/etcd/docs/latest/proxy.html) service to access
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the cluster members in HA fashion.
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The latter relies on a 3rd side reverse proxies, like Nginx or HAProxy, to
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achieve the same goal.
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Etcd
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----
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Etcd proxies are deployed on each node in the `k8s-cluster` group. A proxy is
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a separate etcd process. It has a `localhost:2379` frontend and all of the etcd
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cluster members as backends. Note that the `access_ip` is used as the backend
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IP, if specified. Frontend endpoints cannot be accessed externally as they are
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bound to a localhost only.
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The `etcd_access_endpoint` fact provides an access pattern for clients. And the
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`etcd_multiaccess` (defaults to `false`) group var controlls that behavior.
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When enabled, it makes deployed components to access the etcd cluster members
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directly: `http://ip1:2379, http://ip2:2379,...`. This mode assumes the clients
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do a loadbalancing and handle HA for connections. Note, a pod definition of a
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flannel networking plugin always uses a single `--etcd-server` endpoint!
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Kube-apiserver
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--------------
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K8s components require a loadbalancer to access the apiservers via a reverse
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proxy. Kargo includes support for an nginx-based proxy that resides on each
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non-master Kubernetes node. This is referred to as localhost loadbalancing. It
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is less efficient than a dedicated load balancer because it creates extra
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health checks on the Kubernetes apiserver, but is more practical for scenarios
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where an external LB or virtual IP management is inconvenient.
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This option is configured by the variable `loadbalancer_apiserver_localhost`.
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you will need to configure your own loadbalancer to achieve HA. Note that
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deploying a loadbalancer is up to a user and is not covered by ansible roles
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in Kargo. By default, it only configures a non-HA endpoint, which points to
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the `access_ip` or IP address of the first server node in the `kube-master`
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group. It can also configure clients to use endpoints for a given loadbalancer
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type. The following diagram shows how traffic to the apiserver is directed.
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Note: Kubernetes master nodes still use insecure localhost access because
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there are bugs in Kubernetes <1.5.0 in using TLS auth on master role
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services. This makes backends receiving unencrypted traffic and may be a
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security issue when interconnecting different nodes, or maybe not, if those
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belong to the isolated management network without external access.
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A user may opt to use an external loadbalancer (LB) instead. An external LB
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provides access for external clients, while the internal LB accepts client
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connections only to the localhost, similarly to the etcd-proxy HA endpoints.
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Given a frontend `VIP` address and `IP1, IP2` addresses of backends, here is
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an example configuration for a HAProxy service acting as an external LB:
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```
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listen kubernetes-apiserver-https
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bind <VIP>:8383
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option ssl-hello-chk
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mode tcp
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timeout client 3h
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timeout server 3h
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server master1 <IP1>:443
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server master2 <IP2>:443
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balance roundrobin
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```
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And the corresponding example global vars config:
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```
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apiserver_loadbalancer_domain_name: "lb-apiserver.kubernetes.local"
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loadbalancer_apiserver:
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address: <VIP>
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port: 8383
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```
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This domain name, or default "lb-apiserver.kubernetes.local", will be inserted
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into the `/etc/hosts` file of all servers in the `k8s-cluster` group. Note that
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the HAProxy service should as well be HA and requires a VIP management, which
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is out of scope of this doc. Specifying an external LB overrides any internal
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localhost LB configuration.
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Note: In order to achieve HA for HAProxy instances, those must be running on
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the each node in the `k8s-cluster` group as well, but require no VIP, thus
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no VIP management.
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Access endpoints are evaluated automagically, as the following:
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| Endpoint type | kube-master | non-master |
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|------------------------------|---------------|---------------------|
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| Local LB | http://lc:p | https://lc:sp |
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| External LB, no internal | https://lb:lp | https://lb:lp |
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| No ext/int LB (default) | http://lc:p | https://m[0].aip:sp |
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Where:
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* `m[0]` - the first node in the `kube-master` group;
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* `lb` - LB FQDN, `apiserver_loadbalancer_domain_name`;
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* `lc` - localhost;
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* `p` - insecure port, `kube_apiserver_insecure_port`
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* `sp` - secure port, `kube_apiserver_port`;
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* `lp` - LB port, `loadbalancer_apiserver.port`, defers to the secure port;
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* `ip` - the node IP, defers to the ansible IP;
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* `aip` - `access_ip`, defers to the ip.
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