### What this PR does / why we need it?
For the proxy, we should remove instances when the proxy are not
processing requests.
But sometimes, We need to **isolate** some faulty nodes when a large
number of **requests** are coming in.
So we support to **isolate** faulty nodes by **lowering their priority**
and **deleted** them when the proxy does not process requests.
### Does this PR introduce _any_ user-facing change?
For
`examples/disaggregated_prefill_v1/load_balance_proxy_server_example.py`,
when using `/instances/remove` API to delete the node from the proxy
server:
```txt
curl -X POST http://localhost:9000/instances/remove \
-H "Content-Type: application/json" \
-d '{
"type": "decode",
"instances": "127.0.0.1:8201"
}'
```
There are 2 situations:
* 【New】When the proxy is processing requests, isolate the nodes and
remove them when the proxy is free.
```txt
{"message": "Instances ['127.0.0.1:8201'] are isolated and waiting to be removed.", "current_prefill_instances": ['127.0.0.1:8100', '127.0.0.1:8101'], "current_decode_instances": ['127.0.0.1:8200', '127.0.0.1:8201']}
```
* When the proxy is free, remove the nodes directly.
```txt
{"message": "remove decode instances: ['127.0.0.1:8201'].", "current_prefill_instances": ['127.0.0.1:8100', '127.0.0.1:8101'], "current_decode_instances": ['127.0.0.1:8200']}
```
### How was this patch tested?
- vLLM version: v0.13.0
- vLLM main:
11b6af5280
Signed-off-by: yuxinshan <syx_ctyg@126.com>
7d119df2a9