feat: support setting default http lua_shared_dict

[dennispan]

This addresses the need from #769

[bzp2010]

This solves problems partially, but does not include the prometheus-metrics mentioned in the comment

[bzp2010]

This example is inappropriate, prometheus is defined using the special command for meta { lua_shared_dict }, which cannot be overridden by http { lua_shared_dict }, but it does override other dict values, such as those used by limit-count.

ref: https://github.com/apache/apisix/blob/master/conf/config.yaml.example#L165-L168

This is a special case for creating shared memory between the HTTP subsystem and the stream subsystem.

[dennispan]

@bzp2010 I actually tried meta but it doesn't work. And overriding it under http does

At least it didn't work for me. Maybe I'm missing something.

[bzp2010]

@dennispan

Maybe we can move to another example case that is sure to be ok, so we can merge it first, and if it works on prometheus-metrics, that would solve your problem, and you can report it to community

[Baoyuantop]

@dennispan, can you provide your test steps? Maybe we can find the problem from them.

[dennispan]

I used this to test (after a re-deployment to pick up the configuration changes):

/usr/local/openresty/nginx/sbin/nginx -T \
  -p /usr/local/apisix/ \
  -c conf/nginx.conf \
| grep lua_shared_dict

[dennispan]

@Baoyuantop @bzp2010 any update on this? Anything else needed from me to move this forward?

[nic-6443]

When the Prometheus plugin is not enabled under the stream subsystem (default behavior), http { lua_shared_dict } is useful: https://github.com/apache/apisix/blob/58066abc88df37a490f6c04011ed9588a0bda0d1/apisix/cli/ngx_tpl.lua#L329-L331
so this example can be retained.
@dennispan can you fix CI of this PR? you can run make helm-docs in your local and commit changes of docs.

[swapnil-omni]

This does not work.
The nginx config is like this

lua_shared_dict:
     prometheus-metrics: 20m

This created config like this

lua_shared_dict:
      - prometheus-metrics: 20m

so this should be

{{- range $dict := .Values.apisix.nginx.luaSharedDicts }}
         {{ $dict.name }}: {{ $dict.size }}

https://github.com/apache/apisix/blob/master/conf/config.yaml.example#L250-L276

[dennispan]

Indeed. Here's the pr: #832