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+# Patches to grpc repo tags for the backwards compatibility interop tests
+
+This directory has patch files that can be applied to different tags
+of the grpc git repo in order to run the interop tests for a specific
+language based on that tag.
+
+For example, because the ruby interop tests do not run on the v1.0.1 tag out
+of the box, but we still want to test compatibility of the 1.0.1 ruby release
+with other versions, we can apply a patch to the v1.0.1 tag from this directory
+that makes the necessary changes that are needed to run the ruby interop tests
+from that tag. We can then use that patch to build the docker image for the
+ruby v1.0.1 interop tests.
+
+## How to add a new patch to this directory
+
+Patch files in this directory are meant to be applied to a git tag
+with a `git apply` command.
+
+1. Under the `patches` directory, create a new subdirectory
+titled `<language>_<git_tag>` for the git tag being modified.
+
+2. `git checkout <git_tag>`
+
+3. Make necessary modifications to the git repo at that tag.
+
+4. 
+
+```
+git diff > ~/git_repo.patch
+git checkout <current working branch>
+cp ~/git_repo.patch tools/interop_matrix/patches/<language>_<git_tag>/
+```
+
+5. Edit the `LANGUAGE_RELEASE_MATRIX` in `client_matrix.py` for your language/tag
+and add a `'patch': [<files>,....]` entry to it's `dictionary`.
+
+After doing this, the interop image creation script can apply that patch to the
+tag with `git apply` before uploading to the test image repo.