diaosj opened a new issue, #10992:
URL: https://github.com/apache/apisix/issues/10992
### Description
Hi,
I have some questions about the `least_conn` load balancing algorithm and
would appreciate some clarification:
1. I want to confirm my understanding: When using least_conn, the metric
used is the number of **connections** in Nginx rather than the actual number of
**requests** to the upstream servers.
To achieve load balancing **based on the number of requests**, would it be
necessary to configure Nginx to use a single worker and disable `keepalive`?
Specifically, are these the configurations to adjust?
```yaml
nginx_config:
worker_processes: 1
enable_cpu_affinity: false
worker_rlimit_nofile: 20480
worker_shutdown_timeout: 240s
event:
worker_connections: 10620
http:
keepalive_timeout: 0s
upstream:
keepalive: 320
keepalive_requests: 1000
keepalive_timeout: 0s
```
By doing so, would this effectively balance the load based on the number of
requests received by the upstream servers?
2. Upon reviewing the code for the `least_conn` algorithm, I noticed that
the weight is updated in the `after_balance()` method, which is called during
the `http_log_phase`.
[init.lua](https://github.com/apache/apisix/blob/release/2.7/apisix/init.lua#L681-L683)
```lua
if api_ctx.server_picker and api_ctx.server_picker.after_balance then
api_ctx.server_picker.after_balance(api_ctx, false)
end
```
[least_conn.lua](https://github.com/apache/apisix/blob/release/2.7/apisix/balancer/least_conn.lua#L84-L86)
```lua
local info = servers_heap:valueByPayload(server)
info.score = info.score - info.effect_weight
servers_heap:update(server, info)
```
At this stage, has the request/connection already been released? Could
updating at this time cause a brief inaccuracy in the connection count? Might
this lead to a slight imbalance in the distribution of a small number of
requests?
Thank you for your time and assistance.
### Environment
- APISIX version (run `apisix version`): 2.7
- Operating system (run `uname -a`): Linux
ti-ai-gateway-yuewen-84f46c6c74-2s5qt 5.4.119-1-tlinux4-0009-eks #1 SMP Wed Jan
3 17:12:20 CST 2024 x86_64 x86_64 x86_64 GNU/Linux
- OpenResty / Nginx version (run `openresty -V` or `nginx -V`):
```
nginx version: openresty/1.19.3.2
built by gcc 9.3.1 20200408 (Red Hat 9.3.1-2) (GCC)
built with OpenSSL 1.1.1k 25 Mar 2021
TLS SNI support enabled
configure arguments: --prefix=/usr/local/openresty/nginx --with-cc-opt='-O2
-DNGX_LUA_ABORT_AT_PANIC -I/usr/local/openresty/zlib/include
-I/usr/local/openresty/pcre/include -I/usr/local/openresty/openssl111/include'
--add-module=../ngx_devel_kit-0.3.1 --add-module=../echo-nginx-module-0.62
--add-module=../xss-nginx-module-0.06 --add-module=../ngx_coolkit-0.2
--add-module=../set-misc-nginx-module-0.32
--add-module=../form-input-nginx-module-0.12
--add-module=../encrypted-session-nginx-module-0.08
--add-module=../srcache-nginx-module-0.32 --add-module=../ngx_lua-0.10.19
--add-module=../ngx_lua_upstream-0.07
--add-module=../headers-more-nginx-module-0.33
--add-module=../array-var-nginx-module-0.05
--add-module=../memc-nginx-module-0.19 --add-module=../redis2-nginx-module-0.15
--add-module=../redis-nginx-module-0.3.7 --add-module=../ngx_stream_lua-0.0.9
--with-ld-opt='-Wl,-rpath,/usr/local/openresty/luajit/lib
-L/usr/local/openresty/zlib/lib -L/usr/local/openresty/pcre/lib -L/usr/loca
l/openresty/openssl111/lib
-Wl,-rpath,/usr/local/openresty/zlib/lib:/usr/local/openresty/pcre/lib:/usr/local/openresty/openssl111/lib'
--with-cc='ccache gcc -fdiagnostics-color=always' --with-pcre-jit
--with-stream --with-stream_ssl_module --with-stream_ssl_preread_module
--with-http_v2_module --without-mail_pop3_module --without-mail_imap_module
--without-mail_smtp_module --with-http_stub_status_module
--with-http_realip_module --with-http_addition_module
--with-http_auth_request_module --with-http_secure_link_module
--with-http_random_index_module --with-http_gzip_static_module
--with-http_sub_module --with-http_dav_module --with-http_flv_module
--with-http_mp4_module --with-http_gunzip_module --with-threads --with-compat
--with-stream --with-http_ssl_module```
- etcd version, if relevant (run `curl
http://127.0.0.1:9090/v1/server_info`):
- APISIX Dashboard version, if relevant:
- Plugin runner version, for issues related to plugin runners:
- LuaRocks version, for installation issues (run `luarocks --version`):
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