106 lines
4.5 KiB
Markdown
106 lines
4.5 KiB
Markdown
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
|
|
----
|
|
|
|
Etcd proxies are deployed on each node in the `k8s-cluster` group. A proxy is
|
|
a separate etcd process. It has a `localhost:2379` frontend and all of the etcd
|
|
cluster members as backends. Note that the `access_ip` is used as the backend
|
|
IP, if specified. Frontend endpoints cannot be accessed externally as they are
|
|
bound to a localhost only.
|
|
|
|
The `etcd_access_endpoint` fact provides an access pattern for clients. And the
|
|
`etcd_multiaccess` (defaults to `false`) group var controlls that behavior.
|
|
When enabled, 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. Note, a pod definition of a
|
|
flannel networking plugin always uses a single `--etcd-server` endpoint!
|
|
|
|
|
|
Kube-apiserver
|
|
--------------
|
|
|
|
K8s components require a loadbalancer to access the apiservers via a reverse
|
|
proxy. Kargo 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`.
|
|
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 Kargo. 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.
|
|
|
|
|
|
|
|
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 <VIP>:8383
|
|
option ssl-hello-chk
|
|
mode tcp
|
|
timeout client 3h
|
|
timeout server 3h
|
|
server master1 <IP1>:443
|
|
server master2 <IP2>:443
|
|
balance roundrobin
|
|
```
|
|
|
|
And the corresponding example global vars config:
|
|
```
|
|
apiserver_loadbalancer_domain_name: "lb-apiserver.kubernetes.local"
|
|
loadbalancer_apiserver:
|
|
address: <VIP>
|
|
port: 8383
|
|
```
|
|
|
|
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. Note that
|
|
the HAProxy service should as well be HA and requires a VIP management, which
|
|
is out of scope of this doc. Specifying an external LB overrides any internal
|
|
localhost LB configuration.
|
|
|
|
Note: In order to achieve HA for HAProxy instances, those must be running on
|
|
the each node in the `k8s-cluster` group as well, but require no VIP, thus
|
|
no VIP management.
|
|
|
|
Access endpoints are evaluated automagically, as the following:
|
|
|
|
| Endpoint type | kube-master | non-master |
|
|
|------------------------------|---------------|---------------------|
|
|
| Local LB | http://lc:p | https://lc:sp |
|
|
| External LB, no internal | https://lb:lp | https://lb:lp |
|
|
| No ext/int LB (default) | http://lc:p | https://m[0].aip:sp |
|
|
|
|
Where:
|
|
* `m[0]` - the first node in the `kube-master` group;
|
|
* `lb` - LB FQDN, `apiserver_loadbalancer_domain_name`;
|
|
* `lc` - localhost;
|
|
* `p` - insecure port, `kube_apiserver_insecure_port`
|
|
* `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.
|