Update Force Leave docs (#6550)

Fixes #2742

Previously the docs didn't clarify that if a server restarts as a client then force-leave won't lead to removing the node from the raft config. This is because the node, which is alive after a restart, will refute messages about it having left . These messages about members leaving are in turn what trigger Consul's leader to remove a server from raft.
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@ -11,19 +11,23 @@ description: |-
Command: `consul force-leave` Command: `consul force-leave`
The `force-leave` command forces a member of a Consul cluster to enter the The `force-leave` command forces a member of a Consul cluster to enter the
"left" state. If the member is still actually alive, it will "left" state. The purpose of this method is to force-remove a node that has failed or
eventually rejoin the cluster. The true purpose of this method is to force was shutdown without a [graceful leave](https://www.consul.io/docs/commands/leave.html).
remove "failed" nodes.
Consul periodically tries to reconnect to "failed" nodes in case it is a Consul periodically tries to reconnect to "failed" nodes in case failure was due
network partition. After some configured amount of time (by default 72 hours), to a network partition. After some configured amount of time (by default 72 hours),
Consul will reap "failed" nodes and stop trying to reconnect. The `force-leave` Consul will reap "failed" nodes and stop trying to reconnect. The `force-leave`
command can be used to transition the "failed" nodes to "left" nodes more command can be used to transition the "failed" nodes to a "left" state more
quickly. quickly, as reported by [`consul memebers`](https://www.consul.io/docs/commands/members.html).
This can be particularly useful for a node that was running as a server, This can be particularly useful for a node that was running as a server,
as it will be removed from the Raft quorum. Note that `force-leave` cannot be as it will eventually be removed from the Raft configuration by the leader.
used to force removal of nodes that are outside of the datacenter.
~> Note that for `force-leave` to take full effect the target node's agent must have
shutdown permanently. If the agent is alive and reachable then it will not be removed
from the datacenter's member list nor from the raft configuration. Additionally,
if the agent returns after transitioning to the "left" state, but before it is reaped
from the member list, then it will rejoin the cluster.
## Usage ## Usage
@ -33,3 +37,22 @@ Usage: `consul force-leave [options] node`
<%= partial "docs/commands/http_api_options_client" %> <%= partial "docs/commands/http_api_options_client" %>
## Examples
Remove a node named `ec2-001-staging` from the local agent's datacenter:
```
consul force-leave ec2-001-staging
```
When run on a server that is part of a
[WAN gossip pool](https://learn.hashicorp.com/consul/security-networking/datacenters),
`force-leave` can remove failed servers in other datacenters from the WAN pool.
The identifying node-name in a WAN pool is `[node-name].[datacenter]`.
Therefore, to remove a failed server node named `server1` from
datacenter `us-east1`, run:
```
consul force-leave server1.us-east1
```