Boost Web Performance with OpenResty: Nginx‑Lua Caching, Compression, and Auto‑Refresh

1. OpenResty

OpenResty is a high‑performance web platform built on Nginx and Lua, bundling many Lua libraries, third‑party modules and dependencies. It is used to build dynamic web applications, services and gateways that can handle massive concurrency.

2. Nginx + Redis

Typical architecture: HTTP request → Nginx load balancer → Tomcat → Redis. The chain is serial; if Tomcat fails or its threads are exhausted, responses stall.

By using OpenResty’s lua-resty-redis module, Nginx can read/write Redis directly, bypassing Tomcat threads, so the service remains available even when Tomcat is down, reducing latency and increasing concurrency.

3. Compression to Reduce Bandwidth

For payloads larger than 1 KB, Nginx compresses the data before storing it in Redis, which speeds up Redis reads and saves bandwidth. Compression adds CPU overhead, so data smaller than 1 KB is left uncompressed for higher TPS.

Improves Redis read speed

Reduces bandwidth usage

OpenResty does not provide a built‑in Redis connection pool; a custom Lua implementation is required. Example reference:

http://wiki.jikexueyuan.com/project/openresty/redis/out_package.html

Redis values are stored as JSON objects, e.g. {length:xxx,content:yyy}, where content is the compressed page and length records the original size to decide whether decompression is needed on read.

Compression is performed with the lua-zlib library.

4. Timed Updates

A Lua timer in Nginx periodically fetches the original Tomcat page, stores the HTML in Redis, and refreshes the cache. Cache TTL can be set long (e.g., 1 hour) to survive Tomcat outages, while the timer interval can be short (e.g., 1 minute) for rapid updates.

5. Request Forwarding

When a browser requests a page, Nginx first tries to read the HTML from Redis. If the key is missing, Nginx fetches the page from Tomcat, stores it in Redis, and returns the content to the client.

Nginx reads page HTML from Redis

If Redis miss, fetch from Tomcat and update Redis

Return HTML to browser

6. Single‑Process Timed Update

All Nginx workers can serve front‑end requests, but only worker 0 runs the periodic update. The worker ID is obtained with ngx.worker.id().

7. Configurability

Cache URLs, TTL, and update intervals can be configured via a management backend. An example request:

modify?url=index&&expire=3600000&&intervaltime=300000&&sign=xxxx

The sign is a signature generated from the same parameters using a secret key; Nginx validates the signature before applying the configuration.