Add ADL versioning proposal

Change-Id: I1583bf33eda6685f54fc1ed520fe4f6767e3345b

specs/dsl_versioning_spec.rst

@@ -0,0 +1,95 @@
+==============
+DSL Versioning
+==============
+
+The goal of this spec is creating versioning mechanism for DSL
+
+
+Problem description
+===================
+
+The problem is that our DSL may be changed. Some modifications are
+backward compatible, some of them are not. And we may have situation when
+service file written for old DSL version will be deployed using new fuel-ccp
+tool which does not support that old version of DSL.
+
+Use Cases
+---------
+
+#. User tries to deploy services with newer version than fuel-ccp DSL version,
+   services files are incompatible with fuel-ccp tool.
+#. User tries to deploy services with older or equal version than fuel-ccp DSL
+   version, services files are compatible with fuel-ccp tool
+#. User tries to deploy services with older version than fuel-ccp DSL
+   version, services files are incompatible with fuel-ccp tool
+
+Proposed change
+===============
+
+#. Introduce semver-based DSL versioning in fuel-ccp tool. Version is a number
+   MAJOR.MINOR.PATCH. This version will be defined somewhere in
+   `fuel-ccp repo`. Each service definition will contain minimal DSL
+   version that required for successful deploy.
+   You should increment:
+   #. MAJOR version when you make incompatible changes in DSL;
+   #. MINOR version when you make backwards-compatible changes in DSL;
+   #. PATCH version when you make fixes that do not change DSL, but affect
+      processing flow (will be rarely used).
+#  Check version compatibility during "fuel-ccp deploy" call according next
+   rules:
+   #. if fuel-ccp's DSL version is less than service's DSL version -
+      they are incompatible - error will be printed, deployment will be
+      aborted;
+   #. if MAJOR part of these versions are different - they are incompatible -
+      error will be printed, deployment will be aborted;
+   #. otherwise they are compatible and deploy should be continued.
+#  The initial version for all services and fuel-ccp will be 0.1.0
+
+
+Alternatives
+------------
+
+#. Leave as is, without versioning
+#. Use some existing solution like https://www.python.org/dev/peps/pep-0440/
+#. Invent some another versioning approach
+
+Implementation
+==============
+#. Add versions to all service's repos
+#. Add version to fuel-ccp repo
+#. Add logic to fuel-ccp deploy for handling version validation
+
+Assignee(s)
+-----------
+apavlov
+
+Work Items
+----------
+#. implement patch for fuel-ccp
+#. implement patches for service's repos
+
+Dependencies
+============
+None
+
+
+Testing
+=======
+
+Unit testing for fuel-ccp version validation logic
+
+
+Documentation Impact
+====================
+
+Describe version bump rules
+
+References
+==========
+
+None
+
+History
+=======
+
+None