Ethan-Zhang-ZH opened a new issue, #14022:
URL: https://github.com/apache/apisix/issues/14022
### Description
I'd like to propose two small config-surface enhancements to
`apisix/cli/ngx_tpl.lua`.
Both are currently impossible without patching the template or maintaining a
custom
nginx.conf, but nginx itself fully supports them.
**1. `backlog` for listen sockets**
Currently `node_listen` renders:
```nginx
listen {* item.ip *}:{* item.port *} default_server {% if enable_reuseport
then %} reuseport {% end %};
```
There is no way to tune `backlog=N` from `config.yaml`. Under connection
spikes the
kernel accept queue can overflow (SYN drops, `TCP: request_sock_TCP:
Possible SYN
flooding on port 9080`), and operators have to fix `net.core.somaxconn` on
the host
but still cannot raise nginx's backlog (default 511) for APISIX.
Proposal: allow an optional `backlog` field per listener:
```yaml
nginx_config:
http:
node_listen: # 9080
- ip: 0.0.0.0
port: 9080
backlog: 8192 # optional, absent -> rendered as today
```
**2. `if=` condition for access_log**
Currently the access log is rendered as:
```nginx
access_log {* http.access_log *} main buffer={* http.access_log_buffer *}
flush=3;
```
nginx supports `access_log path [format [buffer=size] [gzip[=level]]
[flush=time] [if=condition]]`
(https://nginx.org/en/docs/http/ngx_http_log_module.html). The condition is
evaluated
in the log phase and can reference variables defined by
`map`/`split_clients`, which
makes things like log sampling or per-status/per-endpoint log exclusion
possible with
plain nginx config — no Lua plugin needed.
Note that nginx's parser treats the 2nd parameter unconditionally as the
format name;
`if=` is only recognized from the 3rd parameter onward. Since the template
already
appends `main` right after the path, an optional `if=` can simply be
inserted after
`main` (before or after `buffer=`, both are accepted), which keeps the
current output
byte-for-byte identical when the option is absent.
Proposal:
```yaml
nginx_config:
http:
access_log_if: $loggable # optional; renders `... main buffer=16384
flush=3 if=$loggable;`
```
The condition variable itself would be declared by users via
`nginx_config.http_configuration_snippet`, e.g. sampling 200s into a
separate file:
```nginx
# http_configuration_snippet
map $status $loggable_200 {
~^200$ $sample_flag;
default 1;
}
map $request_id $sample_flag {
default "";
}
access_log logs/access_200_sample.log main if=$loggable_200;
```
### Motivation
- **backlog**: production gateways behind high-QPS ingress regularly hit
accept-queue
overflow during traffic spikes and restarts (warm-up), and the only
supported knob
today is the host-level `somaxconn`. Exposing `backlog` closes the gap.
- **if=**: log volume is a common operational pain. `if=` is the standard
nginx
mechanism for conditional logging (status filtering, sampling, excluding
health
checks / endpoints with sensitive query params). It would also be the
generic fix
for #10407, which asks for excluding certain endpoints from access logging.
Both changes are template-only (`ngx_tpl.lua` + `conf/config.yaml.example` +
docs),
optional fields, fully backward compatible. I'm willing to submit the PRs.
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