invalidate Nginx cache via ngx-lua

backend.conf

server {
  listen 80;

  server_name backend;

  root /usr/share/nginx/www;
  index index.html index.html;

  location / {
    header_filter_by_lua '
      ngx.header["X-Expire-Content"] = "/random"
    ';
    content_by_lua '
      ngx.say("Adding /random URL to the invalidation queue.")
    ';
  }

  location = /random {
    content_by_lua '
      ngx.say(math.random(100))
    ';
  }
}

frontend.conf

lua_shared_dict expire_queue 10m;

proxy_cache_path  /dev/shm/nginx/ levels=1:2   keys_zone=default:10m;

server {
  listen   80;

  root /usr/share/nginx/www;
  index index.html index.htm;

  server_name frontend;

  location / {
    header_filter_by_lua '
      if ngx.header["X-Expire-Content"] then
        ngx.log(ngx.INFO, "Backend sent invalidation header, adding to the queue " .. ngx.header["X-Expire-Content"])
        ngx.shared.expire_queue:add(ngx.header["X-Expire-Content"],1)
      end
    ';
    
    set_by_lua $http_cache_purge '
      local expire = ngx.shared.expire_queue:get(ngx.var.uri)
        if expire then
          ngx.log(ngx.INFO, "Removing URL from queue and invalidating, " .. ngx.var.uri)
          ngx.shared.expire_queue:delete(ngx.var.uri)
        end
        return expire
      ';

    add_header X-Cached $upstream_cache_status;
    proxy_cache_bypass $http_cache_purge;
    proxy_cache default;
    proxy_cache_valid 200 302 72h;
    proxy_pass http://backend/;
  }
}

test-output

root@precise32:~# wget -S -q -O - frontend/random # Missed request
  HTTP/1.1 200 OK
  Server: nginx/1.1.19
  Date: Fri, 29 Nov 2013 05:24:21 GMT
  Content-Type: application/octet-stream
  Content-Length: 3
  Connection: keep-alive
  X-Cached: MISS
54
root@precise32:~# wget -S -q -O - frontend/random # Cached request
  HTTP/1.1 200 OK
  Server: nginx/1.1.19
  Date: Fri, 29 Nov 2013 05:24:23 GMT
  Content-Type: application/octet-stream
  Content-Length: 3
  Connection: keep-alive
  X-Cached: HIT
54
root@precise32:~# wget -S -q -O - frontend/ # Invalidation queue access
  HTTP/1.1 200 OK
  Server: nginx/1.1.19
  Date: Fri, 29 Nov 2013 05:24:27 GMT
  Content-Type: application/octet-stream
  Content-Length: 44
  Connection: keep-alive
  X-Expire-Content: /random
  X-Cached: MISS
Adding /random URL to the invalidation queue.
root@precise32:~# wget -S -q -O - frontend/random # Cache invalidation request using bypass
  HTTP/1.1 200 OK
  Server: nginx/1.1.19
  Date: Fri, 29 Nov 2013 05:24:31 GMT
  Content-Type: application/octet-stream
  Content-Length: 2
  Connection: keep-alive
  X-Cached: BYPASS
1
root@precise32:~# wget -S -q -O - frontend/random # Cached request
  HTTP/1.1 200 OK
  Server: nginx/1.1.19
  Date: Fri, 29 Nov 2013 05:24:32 GMT
  Content-Type: application/octet-stream
  Content-Length: 2
  Connection: keep-alive
  X-Cached: HIT
1