The Physical Components for Satisfying These New Roles
As SOA was getting baked, technology vendors used different approaches to address the requirements posed by this new services infrastructure. There are the web services management (WSM) vendors who focused on the end-point management of business services. Hardware appliance vendors started off addressing the perimeter space by creating an XML firewall and subsequently adding security functions to it. Last, the technology vendors with a messaging and/or Enterprise Application Integration (EAI) background either evolved their offering or, with their technology expertise, created a software-based middleware solution called Enterprise Service Bus (ESB). While there was no comprehensive solution available, each of the three product types played an important role in the reference architecture.

As each of these solutions started to evolve, they all tried to address the functionality of what we know as the modern ESB. The Web Services Management (WSM) tools did not make significant advancements in messaging and service mediation, but newer hardware appliances started emerging that could function as a service mediator and an integration appliance.

Let’s take a look at the hardware appliances and software ESBs, their characteristics, and the pros and cons of each approach for services infrastructure.

Hardware Appliances
It’s difficult to categorize all hardware appliances in the same bucket. There are a number of appliances in the market; a representative list is available at http://en.wikipedia.org/wiki/XML_appliance.

Usually the hardware appliances have the following strong characteristics:

• XML acceleration: Assisted by a chipset, the appliances can perform fast XML processing including message transformations and schema validations.
• Fast SSL offloading, encryption/decryption of payloads: Once again the ability to use "on the wire" techniques makes these operations efficient in an appliance.
• XML firewall: The ability to keep the "bad guys out" is well enforced by an appliance. It also supports authentication mechanisms to ensure that the entity making the request is indeed the asserted entity.
• Simplicity of setup/operation: As the appliance is a pre-configured box with limited access to actual internals and no peripheral connectivity, it’s fast and easy to set up in the IT infrastructure. It also has a web-based configuration making operational tasks simple as well.

With the pros, come the cons. The hardware appliance suffers from the following drawbacks:

• Upgrades/refreshes: Firmware upgrades especially in band in a production environment can cause disruption. This also plays into the inability to support the latest standards in the SOA space as soon as they are available.
• Stuck with hardware and chipset: The appliance approach is unable to take advantage of new and emerging hardware technologies. You tend to get stuck with the hardware you get. The Moore’s Law effect will naturally force the deployed appliances to become outdated and sluggish in performance.
• Appliance sprawl: A plethora of hardware appliances results in hardware sprawl and increased data center costs. This solution is unable to take advantage of the software virtualization wave that is resulting in lower power consumption and an effective use of capacity.
• Limited integration capability: Even though the hardware appliances are sometimes presented as integration appliances, there is limited support for complex integration patterns (if at all). There is also the inability of extensibility using software (coding) exits.
• Disconnected with the software development process.

It should be noted that there are some hardware appliances that have emerged to address a specific niche problem in services infrastructure.