A simple openresty proxy with metrics endpoint

Dockerfile

FROM openresty/openresty:1.21.4.1-1-alpine

ENV PATH=$PATH:/usr/local/openresty/luajit/bin:/usr/local/openresty/nginx/sbin:/usr/local/openresty/bin

RUN apk update \
    && apk add curl perl \
    # install nginx-lua-openresty https://opm.openresty.org/package/knyar/nginx-lua-prometheus/
    && opm get knyar/nginx-lua-prometheus \
    && mkdir -p /var/log/nginx \
    && mkdir /var/www \
    # clean up nginx default config
    && rm /etc/nginx/conf.d/default.conf \
    && apk del curl perl \
    && rm -rf /var/cache/apk/*

COPY nginx.conf /usr/local/openresty/nginx/conf
COPY prometheus.conf /etc/nginx
COPY proxy.conf /etc/nginx/conf.d

EXPOSE 8080

nginx.conf

error_log  /var/log/nginx/error.log warn;
pid        /var/run/nginx.pid;


events {
    worker_connections  1024;
}


http {
    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';


    access_log /var/log/nginx/access.log main;
    error_log /var/log/nginx/error.log warn;

    sendfile        on;
    #tcp_nopush     on;

    keepalive_timeout  65;

    gzip on;

    include /etc/nginx/prometheus.conf;
    include /etc/nginx/conf.d/*.conf;
}

prometheus.conf

lua_package_cpath "$prefix/resty_modules/lualib/?.so;;";
lua_package_path '/usr/local/openresty/site/lualib/?.lua;;';

lua_shared_dict prometheus_metrics 10M;

init_worker_by_lua_block {
  prometheus = require("prometheus").init("prometheus_metrics")

  metric_requests = prometheus:counter(
    "nginx_http_requests_total", "Number of HTTP requests", {"host", "status"})
  metric_latency = prometheus:histogram(
    "nginx_http_request_duration_seconds", "HTTP request latency", {"host"})
  metric_connections = prometheus:gauge(
    "nginx_http_connections", "Number of HTTP connections", {"state"})
}

log_by_lua_block {
  metric_requests:inc(1, {ngx.var.server_name, ngx.var.status})
  metric_latency:observe(tonumber(ngx.var.request_time), {ngx.var.server_name})
}

proxy.conf

server {
    listen 8080;

    error_log  /var/log/nginx/error.log;
    access_log /var/log/nginx/access.log;
    index index.html;

    location / {
      proxy_pass  http://localhost:80/;
      proxy_set_header X-Forwarded-Host $host;
      proxy_set_header X-Forwarded-Proto $scheme;
    }

    location /nginx_status {
        stub_status;
    }

    location /metrics {
      content_by_lua '
        metric_connections:set(ngx.var.connections_reading, {"reading"})
        metric_connections:set(ngx.var.connections_waiting, {"waiting"})
        metric_connections:set(ngx.var.connections_writing, {"writing"})
        prometheus:collect()
      ';
    }
}