Document describing ONOS release builds

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+# ONOS Release Process Notes
+To release ONOS software builds you will need the following:
+* An account on ONOS Jenkins (jenkins.onosproject.org) with administrator privileges
+* An account on open source sonatype (oss.sonatype.org) with the `org.onosproject` staging profile
+* An account on ONOS gerrit (gerrit.onosproject.org) with push privileges
+
+ONOS releases are done by Continuous Integration (CI) jobs on Jenkins. There
+are two jobs that are run manually when a release is produced:
+* `onos-bazel-release-build` - builds ONOS artifacts, pushes the artifacts to sonatype, tags gerrit repo
+  with the release identifier, and publishes API documentation
+* `onos-docker-build` - builds a docker image for ONOS and pushes it to docker hub
+
+## ONOS version strings
+ONOS uses 3 part version numbers to name releases, using the form `major.minor.patch`. For special purpose builds that
+aren't full releases, a suffix may be added to the patch number to indicate a beta build or a release candidate build.
+* A regular release version looks like `2.5.7` and indicates a fully supported release. These are always built from a
+_support branch_ (more on this later)
+* A beta release may be created at any time during the release cycle. These are used if early access is needed by
+external applications to an ONOS API change, or as a test of the release process. These are versioned like `2.5.7-b1`
+with ascending beta release numbers. Betas may be released from a support branch or `master`
+* A release candidate is created at the end of a release cycle, usually to give QA a chance to test the final versions
+of a release. These are usually built from support branches. They are versioned like `2.5.7-rc1` with ascending
+release candidate numbers.
+
+## Support branches
+Support branches are created late in th release cycle to freeze development of a release and allow further work to
+continue on the `master` branch. Once a support branch is created, any bug fixes to that release must go on `master`
+as well as the support branch. Official releases are _always_ built from support branches. The release branch name is
+derived from the major and minor numbers of the release. So for example, the support branch for ONOS 2.5 is called
+`onos-2.5`. All 2.5 point releases are built from this branch (`2.5.0`, `2.5.1`, etc.)
+
+### Procedure to create a release branch
+```shell
+# Start on master, with an up to date tree
+# set the release branch name here
+export RELEASE="2.5"
+export NEXT_RELEASE="2.6"
+git checkout master
+git pull
+
+# Create the new branch
+git checkout -b onos-$RELEASE master
+
+# now on new branch
+# edit .gitreview, set defaultbranch to new branch name
+defaultbranch=onos-$RELEASE
+
+# push the new branch to gerrit
+git push origin onos-$RELEASE
+
+# commit your change to .gitreview
+# you will have to verify this by hand, there is no verify job for the new
+# branch yet
+git add .gitreview
+git commit -m "bumping to version $RELEASE"
+git review
+
+# go back to master
+git checkout master
+
+# create a new local branch for the next release on master
+git checkout -b branch-$NEXT_RELEASE
+
+# change the versions to be the next release.
+onos-snapshot $NEXT_RELEASE.0-SNAPSHOT
+
+# remove debris left behind by the version setting
+find . -name *.versionsBackup | xargs rm
+
+# put the version changes into gerrit
+git review
+
+# when the verification jobs finish, +2 and submit this change
+
+# now add jobs to verify the new support branch
+# check out the ci-management tree
+# edit jjb/onos/onos-verify.yaml
+# add the new branch to the onos and onos-gui verify jobs
+# submit and merge these changes
+```
+
+## ONOS Artifacts Build
+
+The first step to a release is the ONOS release artifacts build. This will create the JAR files and other artifacts that comprise
+a release, package them, post them to a staging repo on `oss.sonatype.org`, and place a tag in the gerrit repo
+marking the release point.
+
+An artifact release is done using the `onos-bazel-release-build` job on ONOS Jenkins. To begin a release build, go to the [Jenkins
+release build job](https://jenkins.onosproject.org/view/onos-release/job/onos-bazel-release-build/) and click
+_Build with Parameters_ on the menu on the left. A form will come up that is used to specify the parameters for the build.
+The defaults for the build form are to build version 1.15 from the `master` branch. To do a build, we will have to
+change these defaults. In the example given below, we are going to build version `2.5.7` from the `onos-2.5` support branch.
+Note that the string `master` is replaced with our branch name `onos-2.5` in the `STREAM`, `GERRIT_BRANCH`,
+`GERRIT_REFSPEC`, and `sha1` fields. The `ONOS_VERSION` is set to `2.5.7` and the `ONOS_NEXT_VERSION` is set to
+`2.5.8-SNAPSHOT`. The next version always has `-SNAPSHOT` in the name, as it will be used for ongoing development on
+the support branch.
+
+![default build form](images/build-form.png)
+
+When this job is completed, there will be several staging repos created on `sonatype` and the repo will have the tag
+`2.5.7` applied to it.
+
+## ONOS Docker Build
+Once the release build is done and the tag for the release is in place, we can do the docker
+image build. The `onos-docker-build` job on Jenkins will create the docker image based on the tag, and
+push the resulting docker image to DockerHub.
+
+To create the docker image, go to the [docker release build job](https://jenkins.onosproject.org/view/onos-release/job/onos-docker-build/)
+on Jenkins. Click the _Build with Parameters_ link in the menu on the left. A form will come up
+that is used to specify the parameters for the docker image. The defaults for the form are to build from the
+`master` branch. In the example given below, we are going to build a Docker image for the ONOS 2.5.7 release from the `onos-2.5`
+support branch. Note that the string `master` to indicate the branch to build from is
+replaced with `onos-2.5` in the `STREAM`, `GERRIT_BRANCH`, `GERRIT_REFSPEC`, and `sha1` fields.
+In the `ONOS_TAG` field we put the `2.5.7` tag for our release.
+
+![default docker build form](images/docker-form.png)
+
+## Incorporating a New of Release Karaf
+
+These instructions are for the 4.2.14 release. Modify the version number as required.
+
+### Prerequisites
+* gpg
+* md5
+* shasum
+
+### Steps to update karaf:
+* Download base karaf bundle
+```bash
+rm -rf /tmp/karaf && mkdir -p /tmp/karaf
+cd /tmp/karaf && curl -O https://dlcdn.apache.org/karaf/4.2.14/apache-karaf-4.2.14.tar.gz
+```
+* Upload base karaf to maven central
+```bash
+export SONATYPE_USER=<your-user>
+export SONATYPE_PASSWORD=<your-password>
+$ONOS_ROOT/tools/build/push-karaf 4.2.14 /tmp/karaf
+```
+
+* Publish the new karaf bits:
+    * Log into sonatype and release the staging repo
+    * Update ONOS to use new base version
+    * Update deps.json to change the karaf references from the old release to the new one
+    * Run onos-lib-gen
+    * Update tools/package/etc files to refer to the new karaf version (may require merging changes)
+        * org.apache.karaf.features.cfg
+        * startup.properties
+
+* Update packaging tools (these all have references to the karaf version)
+    * tools/package/bin/onos-backup
+    * tools/package/bin/onos-restore
+    * tools/package/dependencies/template.pom
+    * tools/package/onos-prep-karaf
+    * tools/package/onos_stage.py
+    * tools/package/deb/prerm
+
+* Update build tools
+    * tools/build/bazel/osgi_features.bzl
+    * tools/build/envDefaults
+
+* Update test tools
+    * tools/test/bin/onos-check-bits
+
+* Test ONOS
+    * bazel run onos-local clean
+    * make sure CLI comes up
+    * make sure GUI comes up
+* Create offline karaf bundle (need a cell node for this)
+
+```shell
+export KARAF_RELEASE_VERSION=4.2.14
+
+export OC1=<cell IP>
+
+cd /tmp/karaf && $ONOS_ROOT/tools/build/build-offline-karaf
+```
+
+* Upload offline karaf bundle (it will be named with today's date)
+
+```shell
+$ONOS_ROOT/tools/build/push-karaf 4.2.14-offline-20220105 /tmp/karaf
+```
+
+* Publish the new offline karaf bits
+    * Log into sonatype and release the staging repo
+* Modify ONOS to use offline bundle
+    * Edit deps.json to refer to the offline bundle
+    * Run onos-lib-gen
+    * Test ONOS
+* Finish off the PR
+    * Merge your changes locally and make a gerrit PR. All done!
+
+### Side projects requiring an update
+
+* aether-pod-configs
+* cord-ci-management
+* onos-helm-charts
+* sdfabric-docs
+* sdfabric-helm-charts
+* up4
+* tost-onos
+* voltha-onos
+
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