[+] update README for Patroni as DCS type, fixes #275 (#276)

Fixes #275

Author: mbanck-cd

README.md

@@ -117,11 +117,11 @@ This is a list of all avaiable configuration items:
 `ip`                | `VIP_IP`              | yes       | 10.10.10.123              | The virtual IP address that will be managed.
 `netmask`           | `VIP_NETMASK`         | yes       | 24                        | The netmask that is associated with the subnet that the virtual IP `vip` is part of.
 `interface`         | `VIP_INTERFACE`       | yes       | eth0                      | A local network interface on the machine that runs vip-manager. Required when using `manager-type=basic`. The vip will be added to and removed from this interface.
-`trigger-key`       | `VIP_TRIGGER_KEY`     | yes       | /service/pgcluster/leader | The key in the DCS that will be monitored by vip-manager. Must match `<namespace>/<scope>/leader` from Patroni config. When the value returned by the DCS equals `trigger-value`, vip-manager will make sure that the virtual IP is registered to this machine. If it does not match, vip-manager makes sure that the virtual IP is not registered to this machine.
-`trigger-value`     | `VIP_TRIGGER_VALUE`   | no        | pgcluster_member_1        | The value that the DCS' answer for `trigger-key` will be matched to. Must match `<name>` from Patroni config. This is usually set to the name of the patroni cluster member that this vip-manager instance is associated with. Defaults to the machine's hostname.
+`trigger-key`       | `VIP_TRIGGER_KEY`     | yes       | /service/pgcluster/leader | The key in the DCS or the Patroni REST endpoint (e.g. `/leader`) that will be monitored by vip-manager. Must match `<namespace>/<scope>/leader` from Patroni config. When the value returned by the DCS equals `trigger-value`, vip-manager will make sure that the virtual IP is registered to this machine. If it does not match, vip-manager makes sure that the virtual IP is not registered to this machine.
+`trigger-value`     | `VIP_TRIGGER_VALUE`   | no        | pgcluster_member_1        | The value that the DCS' answer for `trigger-key` will be matched to. Must match `<name>` from Patroni config for DCS or the HTTP response for Patroni REST API. This is usually set to the name of the Patroni cluster member that this vip-manager instance is associated with. Defaults to the machine's hostname or to 200 for Patroni.
 `manager-type`      | `VIP_MANAGER_TYPE`    | no        | basic                     | Either `basic` or `hetzner`. This describes the mechanism that is used to manage the virtual IP. Defaults to `basic`.
 `dcs-type`          | `VIP_DCS_TYPE`        | no        | etcd                      | The type of DCS that vip-manager will use to monitor the `trigger-key`. Defaults to `etcd`.
-`dcs-endpoints`     | `VIP_DCS_ENDPOINTS`   | no        | http://10.10.11.1:2379    | A url that defines where to reach the DCS. Multiple endpoints can be passed to the flag or env variable using a comma-separated-list. In the config file, a list can be specified, see the sample config for an example. Defaults to `http://127.0.0.1:2379` for `dcs-type=etcd` and `http://127.0.0.1:8500` for `dcs-type=consul`.
+`dcs-endpoints`     | `VIP_DCS_ENDPOINTS`   | no        | http://10.10.11.1:2379    | A url that defines where to reach the DCS or Patroni REST API. Multiple endpoints can be passed to the flag or env variable using a comma-separated-list. In the config file, a list can be specified, see the sample config for an example. Defaults to `http://127.0.0.1:2379` for `dcs-type=etcd`, `http://127.0.0.1:8500` for `dcs-type=consul` and `http://127.0.0.1:8008` for `dcs-type=patroni`.
 `etcd-user`         | `VIP_ETCD_USER`       | no        | patroni                   | A username that is allowed to look at the `trigger-key` in an etcd DCS. Optional when using `dcs-type=etcd` .
 `etcd-password`     | `VIP_ETCD_PASSWORD`   | no        | snakeoil                  | The password for `etcd-user`. Optional when using `dcs-type=etcd` . Requires that `etcd-user` is also set.
 `consul-token`      | `VIP_CONSUL_TOKEN`    | no        | snakeoil                  | A token that can be used with the consul-API for authentication. Optional when using `dcs-type=consul` .
@@ -133,6 +133,8 @@ This is a list of all avaiable configuration items:
 `etcd-key-file`     | `VIP_ETCD_KEY_FILE`   | no        | /etc/etcd/client.key.pem  | A private key for the client certificate, used to decrypt messages sent by etcd endpoints. Required when `etcd-cert-file` is specified.
 `verbose`           | `VIP_VERBOSE`         | no        | true                      | Enable more verbose logging. Currently only the manager-type=hetzner provides additional logs.
 
+## Configuration - Patroni REST API
+To directly use the Patroni REST API, simply set `dcs-type` to `patroni` and `trigger-key` to `/leader`. The defaults for `dcs-endpoints` (`http://127.0.0.1:8008`) and `trigger-value` (200) for the Patroni checker should work in most cases.
 
 ## Configuration - Hetzner
 To use vip-manager with Hetzner Robot API you need a Credential file, set `hosting_type` to `hetzner` in `/etc/default/vip-manager.yml`