SOAP ( Simple Object Access Protocol) is a message protocol that allows distributed elements of an application to communicate. SOAP can be carried over a variety of lower-level protocols, including the web-related Hypertext Transfer Protocol (HTTP). SOAP defines a header structure that identifies the actions that various SOAP nodes are expected to take on the message, in addition to a payload structure for carrying information. The concept of routing a message through a string of nodes that perform different functions is how SOAP supports things like addressing, security and format-independence. Essentially, the headers identify roles, which in turn provide the SOA features which SOAP then routes to. Stringing messages through a sequence of steps is uncommon in today’s microservice-centric development environments.

SOAP is an integral part of the service-oriented architecture (SOA) and the Web services specifications associated with SOA. Because it allows the sender to create a message route based on the logical services that have to be applied to the message on the way to its destination, it lends itself to providing secure and compliant connections, controlling access, offering reliable delivery and failure recovery, and supporting dynamic service discovery. SOA without SOAP is difficult to imagine.