Add docker hierarchy to readme

README.md

@@ -6,6 +6,54 @@ See the documentation in the 'docs' folder for build and usage
 instructions.
 
 
+## Docker hierarchy and release tagging
+
+When updating Dockerfiles, and especially the tags in the `.release` files,
+it is useful to know the hierarchy.  All downstream images must have the release
+tags updated.
+
+The release tags should match the underlying dependencies used.  E.g., for the
+first release of cppTango 9.3.4-rc4, use the tag `9.3.4-rc4`.  If there are
+subsequent modifications to a Dockerfile, but still using that cppTango release,
+add a suffix, e.g., `9.3.4-rc4.1`.  Further changes would then incremenent that
+suffix: `9.3.4-rc4.2`, etc.
+
+- ubuntu
+  - deploy/Dockerfile:FROM ubuntu:18.04
+  - tango-builder/Dockerfile:FROM ubuntu:18.04
+- debian-buster-slim
+  - tango-dependencies/Dockerfile:FROM debian:buster-slim as buildenv
+  - tango-dependencies/Dockerfile:FROM debian:buster-slim
+    - tango-java/Dockerfile:FROM {nexus}/tango-dependencies:latest
+        - hdbpp_viewer/Dockerfile:FROM {nexus}/tango-java:latest
+        - tango-jive/Dockerfile:FROM {nexus}/tango-java
+        - tango-pogo/Dockerfile:FROM {nexus}/tango-java:latest
+        - tango-rest/Dockerfile:FROM {nexus}/tango-dependencies:latest as buildenv
+        - tango-rest/Dockerfile:FROM {nexus}/tango-java:latest
+        - tango-vnc/Dockerfile:FROM {nexus}/tango-java:latest
+    - tango-cpp/Dockerfile:FROM {nexus}/tango-dependencies:latest as buildenv
+    - tango-cpp/Dockerfile:FROM debian:buster-slim
+      - tango-archiver/Dockerfile:FROM {nexus}/tango-cpp:latest
+      - tango-dsconfig/Dockerfile:FROM {nexus}/tango-cpp:latest
+      - tango-libtango/Dockerfile:FROM {nexus}/tango-cpp
+        - tango-admin/Dockerfile:FROM {nexus}/tango-libtango:latest
+        - tango-test/Dockerfile:FROM {nexus}/tango-libtango:latest
+        - tango-databaseds/Dockerfile:FROM {nexus}/tango-libtango:latest
+      - ska-python-buildenv/Dockerfile:FROM {nexus}/tango-cpp:latest
+        - ska-python-runtime/Dockerfile:FROM {nexus}/ska-python-buildenv:latest as buildenv
+        - ska-python-runtime/Dockerfile:FROM {nexus}/tango-cpp:latest
+          - tango-itango/Dockerfile:FROM {nexus}/ska-python-buildenv:latest as buildenv
+          - tango-itango/Dockerfile:FROM {nexus}/ska-python-runtime:latest
+          - tango-pytango/Dockerfile:FROM {nexus}/ska-python-buildenv:latest as buildenv
+          - tango-pytango/Dockerfile:FROM {nexus}/ska-python-runtime:latest
+          - tango-vscode/Dockerfile:FROM {nexus}/ska-python-buildenv:latest as buildenv
+          - tango-vscode/Dockerfile:FROM {nexus}/ska-python-runtime:latest
+      - tango-starter/Dockerfile:FROM {nexus}/tango-cpp:latest
+- mariadb
+  - tango-db/Dockerfile:FROM mariadb:10
+    - mariadb_hdbpp/Dockerfile:FROM {nexus}/tango-db:latest
+
+
 ## HDB++ Archiver Implementation
 
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