OpenResty rate limiter example

nginx.conf

worker_processes 1;
error_log logs/error.log;
events {
    worker_connections 1024;
}
http {
    lua_shared_dict token_bucket 10m;

    init_by_lua '
        ngx.shared.token_bucket:set("tokens_avail", 0)
        ngx.shared.token_bucket:set("last_timestamp", os.time())
    ';

    server {
        listen 8098;
        location / {
            default_type text/html;
            access_by_lua '
                local TOKEN_ACCUM_RATE = 0.1
                local BUCKET_SIZE = 5
                local TOKENS_PER_REQ = 1
                local last_timestamp = ngx.shared.token_bucket:get("last_timestamp")
                local cur_timestamp = os.time()
                local time_elapsed = cur_timestamp - last_timestamp
                local tokens_accum = time_elapsed * TOKEN_ACCUM_RATE
                local tokens_avail = ngx.shared.token_bucket:get("tokens_avail")
                tokens_avail = math.min(tokens_avail + tokens_accum, BUCKET_SIZE)
                if tokens_avail >= TOKENS_PER_REQ then
                    ngx.shared.token_bucket:set("tokens_avail", tokens_avail - TOKENS_PER_REQ)
                    ngx.shared.token_bucket:set("last_timestamp", cur_timestamp)
                    ngx.exit(ngx.OK)
                else
                    -- we have to set the status here because we call ngx.say(),
                    -- forcing response headers to be sent immediately
                    -- https://github.com/openresty/lua-resty-redis/issues/15#issuecomment-14747652
                    ngx.status = 429
                    ngx.say(tokens_avail)
                    ngx.say("Request failed")
                    ngx.exit(429)
                end
            ';

            content_by_lua '
                ngx.say(ngx.shared.token_bucket:get("tokens_avail"))
                ngx.say("Request successful")
            ';
        }
    }
}