Are you designing Microservices? So, I would like to share a fascinating slide deck that I discovered recently. That comes from a Patt Helland’s talk at TechEd 2002 (!!).

Defining Fiefdoms

Using the author’s definition, we could define a Fiefdom as:

  1. Computing function and applications which behaves as an independent entity
  2. Has private data
    1. No one outside can read or write the information
    2. Only well-defined requests are serviced from the outside
  3. An autonomous unit — managed independently (Usually one (or a few) machines)
  4. Don’t trust outsiders
    1. Incoming requests will be inspected
    2. Fields will be validated
    3. Identity will be authenticated

It looks like Microservices. Am I right?

Defining Emissaries

Using the author’s definition, we could define an Emissary as:

  1. It knows how to fill out a request for the fiefdom
  2. It understands the rules of the fiefdom and how to (probably) get the request accepted
  3. They have two purposes
    1. Displaying information to users
    2. Preparing requests to send to fiefdoms
  4. They are not trusted by the fiefdom
  5. They will frequently come with reference data
  6. They gather information needed to prepare requests (For example, a shopping basket accumulates the items to purchase)

It looks like the Client APIs!


The slide deck is impressive. There are plenty of architectural insights that are still valid today. I strongly recommend you to spend some time getting it. It is a valuable resource.

Cover: Jonas Verstuyft

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