I recently worked on a project for a client that (still) uses Subversion for their code repositories. Unfortunately they had no real short-term interested in migrating their code to Git, which left the team without such goodies as merge/pull requests, easy branching and all the other advantages that Git provides. Git actually has a built-in tool called 'git-svn'. Its main purpose is to migrate from Subversion to Git, or at the most do one-way syncing. In my case, two-way synchronization was the only option, since the Subversion repository was also used by another independent team.
After some experimentation I created a script that was able to do 2-way synchronization without too many problems, though this was just on my local machine, and we needed a solution for the entire team.
Jenkins, Containers & Gitlab to the rescue!
What I came up with was to build a Jenkins pipeline script that does the heavy lifting of synchronizing between git and subversion, while also integrating a Continuous Integration pipeline so that the main codebase is kept stable and thus *should* never break.
Fortunately the client was nice enough to provide us with a bare-bones RHEL 7 VM, and from there, I created a containerized CI/CD suite with containers for Jenkins, Gitlab, Sonar and a local Artifactory for snapshot build management. I created 2 Jenkins pipeline scripts for each project, one to do the git-svn synchronizations, and one to run a ci/cd pipeline that sets up an ad-hoc Docker container for the app (and one for the DB), and runs build & tests against them.
This CI/CD pipeline is triggered both by opened merge requests into the develop branch (no one is allowed to commit directly to develop/master branches), and by the git-svn sync pipeline script. The latter synchronizes between the master branch of git and the subversion repository and triggers the CI/CD pipeline in reverse order, that is, it rebases SVN code into master, and after the CI/CD pipeline successfully passes, merges the code into develop. This way, the develop branch is protected from broken build commits both from SVN and from feature branches.
I created a demo project with examples of the pipeline script and a full-fledged containerized solution you can use as a starting point: