Merge pull request #50 from gradescope/ibrahim/ch37009/document-how-i…

…nstructors-can-run-their-autograder

Add a documentation section for running docker images locally

docs/manual_docker.md

@@ -22,3 +22,32 @@ image, so you can organize it as you wish.
 If your Docker Hub repository is private, you'll need to give the user
 `gradescopeecs` access to your repository. You may want to do this to
 make sure that students cannot download your autograder image.
+
+## Running autograder images locally
+
+To run your autograder image locally, you will currently need to bypass our
+autograder harness because otherwise it will try to communicate with Gradescope
+by default. You can do this by mounting a sample submission into the
+`/autograder/submission` directory and then running `/autograder/run_autograder`
+directly. Here's an example command; replace the path to the submission and
+Docker image name with the appropriate values.
+
+```bash
+docker run --rm -v /path/to/submission:/autograder/submission username/image_name:tag bash -c "mkdir /autograder/results && /autograder/run_autograder && cat /autograder/results/results.json"
+```
+
+or to start an interactive session:
+
+```bash
+docker run --rm -it -v /path/to/submission:/autograder/submission username/image_name:tag bash
+```
+
+Minor notes:
+
+- `--rm` is added to clean up the container after it exits. You can remove it if
+  you want to inspect container logs or state afterwards.
+- The `/autograder/results` directory is ordinarily created by the harness, so
+  that's why you need to mkdir it. When running an interactive bash session you
+  will need to create it too.
+- In the first example, we're using `bash -c "..."` to run multiple commands in
+  one Docker command and then show the results.