MT#62949 build README

Change-Id: I48f1c07d4de1b7d3f50725027fb9248ac7742945

build/README.md

@@ -0,0 +1,56 @@
+build
+=====
+
+This app is in charge of the building process of releases.
+
+It reads the yaml files from sipwise-repos-scripts package in order to
+find out everything related to a release.
+
+```python
+REPOS_SCRIPTS_CONFIG_DIR = "/usr/share/sipwise-repos-scripts/config"
+```
+
+The [release yaml](fixtures/config/trunk.yml) file is the one source of truth related
+to a release:
+
+* debian_release
+* release-mrX.Y[.Z]?: backports to be included in the release repository
+* jenkins-jobs: jenkins jobs related info
+* release_mirror: steps to do on release process
+
+But for build the most important part of the file is ``jenkins-jobs``.
+There are ``projects`` and ``build_deps`` defined.
+
+``build_deps`` is a list of projects that are a build dependency of others. Like:
+
+```yaml
+jenkins-jobs:
+  build_deps:
+    data-hal:
+      - ngcp-panel
+    ngcp-schema:
+      - ngcp-panel
+    libinewrate:
+      - sems-pbx
+    libswrate:
+      - kamailio
+      - sems-pbx
+    libtcap:
+      - kamailio
+      - lnpd
+    sipwise-base:
+      - ngcp-panel
+      - ngcp-schema
+    check-tools:
+      - snmp-agent
+```
+
+In this example ``data-hal`` needs to be built *before* ``ngcp-panel``. ``sipwise-base`` has
+to be built *before* ``ngcp-panel`` and ``ngcp-schema`` and so on.
+
+``build`` app has the logic to resolve this dependency hierarchy so triggering the right project in the right moment.
+
+``build`` triggers jenkins jobs and when the job finishes the next in the queue is triggered.
+It keeps the info of what project has been triggered, built or failed.
+
+``build`` depends on [repoapi](../repoapi/models/jbi.py) JenkinsBuildInfo