dx-proxy-cache

Proxy Cache

Programmable reverse caching proxy. Use as a stand-alone app or an express middleware. Comes with TTL and MongoDB adapters.

Features

• Request pooling: multiple requests with a cache miss will be pooled, i.e. only one request will be made upstream
• Fast in memory caching -- adapter cache are used as a second layer
• Extensible Adapter API
• Express middleware compatible
• Gzip compression when using the stand-alone server
• Stale-caching: serve stale cache while updating the cache object asynchronously in the background
• Remove cache objects (largest and least hit ones first) after a set memory threshold (defaults to 2GiB)

Install

npm install rn-proxy-cache

Usage

Stand-alone server with simple global-TTL caching

Note the --spoof-host-header option rewrites your "Host" header value to match the target host value. You probably won't use this in a normal proxy-cache setup unless you're running some sort of mirror site.

npm start \
--target-host="highscalability.com:80" \
--proxy-port=8080 \
--spoof-host-header \
--ttl=30000

• --target-host="www.google.com:80": your upstream host.
• --proxy-port=8080: the port for this proxy server.
• --spoof-host-header: use this to rewrite Host header value to the --target-host value. Only useful if your upstream application needs to use the domain specified by the --target-host value.
• --ttl=30000: TTL caching in milliseconds, defaults to 600000ms (10 minutes)

Stand-alone server using MongoDB as a global cache expire schedule and persistent cache storage

npm start \
--target-host="www.apple.com:80" \
--proxy-port=8080 \
--spoof-host-header \
--mongodb-url="mongodb://localhost:27017/test" \
--use-external-cache \
--watch-interval=60000 \

• --mongodb-url: Supply this to use the MongoDB adapter. Will watch the PublishSchedule collection that contains documents with the publish_date ISO Date string field and clears cache accordingly.
• --use-external-cache: Enables storing cached objects in the external storage interface provided by the adapter, useful if you run multiple instances of the proxy or surviving restarts
• --watch-interval: How long between each time it checks the PublishSchedule collection. Defaults to 30sec.

Additional parameters when running as a stand-alone server

• --mem-usage: Shows memory usage info every 30sec.
• --verbose-log: Verbose logging for debugging.

Express middleware

var ProxyCache = require('rn-proxy-cache'),
    express = require('express'),
    app = express();

var proxyCache = new ProxyCache({
    targetHost: "highscalability.com:80",
    spoofHostHeader: true // again, doubt you need to enable this if you're running your own site
});

app.use(proxyCache.createMiddleware());

proxyCache.ready.then(function() {
    app.listen(8181, function () {
        console.log("ProxyCache server is ready");
    });
});

Use new ProxyCache(options) to create a new instance of the proxy cache. options are:

• targetHost: the upstream host to proxy to. Defaults to "localhost:80"
• httpProtocol: "http" or "https", defaults to "http".
• Adapter: the cache adapter module to use, see lib/adapters for examples. Defaults to the TTL adapter.
• adapterOptions: adapters are passed these options when constructed, i.e. new Adapter(proxyCacheInstance, options)
• httpProxyOptions: upstream proxy requests are made using http-proxy, these options are passed to the httpProxy.createProxyServer() method.
• allowStaleCache: allow stale cache to be served while asynchronously making a request upstream to update the cache object.
• spoofHostHeader: rewrite the upstream request header Host value to match targetHost
• memGiBThreshold: the maximum memory threshold before cleaning up some less hit cache objects to free memory

Optionally set req.shouldCache to let ProxyCache know if a request should be cached.

Creating a custom Adapter

To implement a custom Adapter, create a node module with the following constructor interface: CacheAdapter(proxyCache, options){ ... }.

There are 2 things you can do with a custom adapter:

1. Decide when to invalidate the memory cache by calling proxyCache.clearAll()
2. Implement external cache storage with the following interfaces as CacheAdapter's prototype methods: setCache(key, value), getCache(key), clearCache(), all returning a promise that resolves when the task is completed.

Finally if you need to init the adapter asynchronously, you can set a .ready promise property on the adapter instance and resolve when ready.

Notes

• "host-rewrite" option is disabled for redirects.
• Response status codes from upstream that's greater than 200 are not cached.
• Empty response bodies are not cached.
• mobile-detect is used to generate part of the cache key prefix: phone or not_phone. This should be the most common case of upstream response variations. Ideally, we should use Vary headers provided by upstream responses.

TODOs

Pull requests are welcome :)

• Expose ProxyCache instance in express routes -- http.ClientRequest#proxyCache
• Express middleware API, e.g. proxyCache.createMiddleware(app, /\/api\/.*/, { targetProtocol: 'https', targetHost: 'localhost:8081', rewriteUrl: rewriteUrlMethod })
• When targetHost is not provided, set upstream to the local response stream (aka http.ServerResponse object in the express route), instead of the proxy response generate with http-proxy
• Support ETag for browsers and Vary for upstream response variations. See RFC2616 for more.
• Dockerfile, systemd unitfile templates, and other proc management files
• Add feature to regenerate cache (precache), generating the ones with the most cache hits first
• Add option to override ProxyCache.prototype.getCacheKey method
• Handle very large responses?