ISPPlanet Cache Review Series - Wrap-Up

Cache Deployment
Every product we tested was able to simultaneously cache HTTP in forward proxy and transparent modes. All but InfoLibria cache FTP in forward proxy mode; none caches FTP in transparent mode. These are the baseline features one should expect from any web cache.

What protocols makes a cache more versatile? Only NetApp proxies NNTP (a $3,000 option, which is included in our as-tested price). NetCache users vouch for the utility of this feature: One reader, Jouni Pohjola, told me a university in Finland increased news download speed from 5 articles per second to 68 by deploying NetCache. But other vendors state they do not see market demand.

Streaming media is on every vendor's horizon, but expect differences in packaging. NetApp charges a per-protocol license fee for RTSP and MMS -- and was the only vendor with multimedia available during our evaluation. InfoLibria markets companion product streaming multimedia server, MediaMall. CacheFlow intends to embed streaming media support in CacheOS, making it a standard feature of the base product.

Forward proxies require client config, so many ISPs prefer transparent mode. All of these products can be deployed with a layer 4 switch for transparent caching. InfoLibria also sells its own electro-mechanical bridge for fail-safe "no power" in-line transparency. On the other hand, InfoLibria was the only vendor not yet shipping WCCP redirection (v2 now in beta). Each vendor maintains a list of tested redirectors -- for best support, pair with products on that list. We found the most thorough config info on third-party switch and router redirection at CacheFlow.

Every product tested can act as a web accelerator (reverse proxy). But, as reader Daniel Chandran observed, "These are really forward proxy products which implement only a subset of reverse proxy functionality." NICS products had the most granular acceleration controls, including load distribution across back-end servers with identical content and response header rewriting. We recommend combining cache-based acceleration with an L4 or L7 switch for efficient load-balanced server clusters.

All of these caches can share workload in a hierarchy as an ICP child, peer, or parent. Beyond this, we found diversity. Squid can distribute a cache digest used by others to locate content without queries. CacheFlow can deflect HTTP requests to primary or alternate gateways, or to forward hosts and groups. Unlike static ICP or forward hierarchies, InfoLibria's DynaLink dynamically sheds load to upstream caches during periods of high volume -- but admins can't control which requests are shed. Every product we tested supported hierarchy bypass; most could bypass with "proxy only" to distribute object storage across a hierarchy.

When caching is added to a network, it becomes a critical path resource. Transparency can redirect around a downed cache: L4 switches can avoid a non-responsive cache; a DynaLink "watchdog" detects DynaCache failure. Hierarchies can be used to build cache clusters for high availability. Some products include a configurable cluster status monitor: NICS caches know if they are primary, backup, or offline, and NetCaches can be deployed in "takeover pairs."

These products are all pretty flexible, capable of supporting many roles and protocols. The tested DynaCache release was the most limited, with broader protocol support now in beta. On the other hand, NetCache had us test their beta, affording a hands-on look at NetApp's newest features. But, whether we consider only the current shipping release or include next release features, NetCache stands out as the most versatile cache in this crowd.